tag:blogger.com,1999:blog-14733803885694727792024-03-13T08:19:33.149-04:00Dream of the Open Channel"The dream is to find the open channel." --- Richard Feynman
<br>A blog using the scientific search for intelligent life on other worlds as a mental lens to ask every sort of interesting question.Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.comBlogger63125tag:blogger.com,1999:blog-1473380388569472779.post-76168101342943962972020-04-12T21:22:00.002-04:002020-04-12T21:22:22.992-04:00Wow! Signal Pub 2 - let's talk.<a href="https://www.wowsignalpodcast.com/2020/04/join-us-for-wow-signal-pub-2.html" target="_blank">It will be next Friday night,</a> and I hope to see lots of people there. I know it's not the best time for people in Europe, but we'll do some a few hours earlier in the day so people in Europe can join in without staying up to the wee hours.<br />
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Last Friday, we did a technical rehearsal, which went well. Feel free to <a href="https://youtu.be/DLnG2OrqeXo" target="_blank">watch it on YouTube</a> if you want. It's almost a Pub 1.5.<br />
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<br />Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-37672912464104003982019-06-14T17:29:00.001-04:002019-06-17T21:30:11.817-04:00More Aladin on a rainy day - Gaia Alert 16bao<div dir="ltr" style="text-align: left;" trbidi="on">
<b><i>Update 17 Jun 2019</i></b>: Some folks on /r/KIC8462852 think this is probably an eclipsing binary, and they make a decent case, but I still have questions.<br />
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Am I really onto something here? Well, let's just look at the facts as I can dig them up and see where it leads.<br />
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The star first came to my attention as the source of <a href="http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia16bao/" target="_blank">Gaia Alert 16bao</a> which I have been following for some time now. Gaia has photometric data for this star (I'm pretty sure it's a star, as I can discuss later) going back to October of 2014, and the latest available is May of 2019 as of this writing, for a total span of 1674 days.<br />
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Here is the light curve from <a href="http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia16bao/" target="_blank">Gaia alert 16ba</a>o:<br />
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<a href="https://1.bp.blogspot.com/-orVMbGUtdrU/XQKnIq6lRuI/AAAAAAAA39M/TR4aLbXZJRQ2gCVIhj3AM73L0SyOCIeiwCLcBGAs/s1600/16bao_lightcurve.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://1.bp.blogspot.com/-orVMbGUtdrU/XQKnIq6lRuI/AAAAAAAA39M/TR4aLbXZJRQ2gCVIhj3AM73L0SyOCIeiwCLcBGAs/s640/16bao_lightcurve.png" width="640" /></a></div>
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What we see are as many as 6 sharp dips over the course of about 800 days, and the rest of the time the brightness of the star is about steady. The deepest of this dips is about 1.7 magnitudes, which is very deep - about 79% dimming for a short time - over about 20 hours before recovering over about 10 hours. The sharpness and irregular spacing of the dips is reminiscent of <a href="https://disownedsky.blogspot.com/2017/11/im-still-perplexed-tabbys-star-update.html" target="_blank">Boyajian's Star</a>. The dips are too deep, aperiodic and irregular for an eclipsing binary.<br />
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The Gaia alert gives the J2000 coordinates <span style="font-family: "times" , "times new roman" , serif;">as RA=<span style="background-color: white; color: #333333;">297.72688 degrees , and </span><span style="background-color: white; color: #333333;">Dec</span><span style="background-color: white; color: #333333;"> = 23.55513 </span><span style="background-color: white; color: #333333;">degrees. We can plug this straight into <a href="https://aladin.u-strasbg.fr/" target="_blank">Aladin Sky Atlas</a> to see what's there. Right away we can learn several things.</span></span><br />
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<span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">Here's the image I get when I load in the ALLWISE color image:</span></span><br />
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<a href="https://1.bp.blogspot.com/-xEE4GGETITE/XQKtr5p3tFI/AAAAAAAA39Y/EkLRBcQGexsa3NXM39rTyMlB2oNhu7Y8wCLcBGAs/s1600/16bao_allwise_color.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="512" data-original-width="891" height="364" src="https://1.bp.blogspot.com/-xEE4GGETITE/XQKtr5p3tFI/AAAAAAAA39Y/EkLRBcQGexsa3NXM39rTyMlB2oNhu7Y8wCLcBGAs/s640/16bao_allwise_color.png" width="640" /></a></div>
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<span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">This is in the galactic plane, so things get a little crowded. Now here's the Panstarrs image: </span></span><br />
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<a href="https://1.bp.blogspot.com/-BbfytXDKOH0/XQK4RjybDEI/AAAAAAAA39k/yOqioAmf7FYFe7mBhcx1StjoZYg8MNhxgCLcBGAs/s1600/pan_starrs_16bao.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="512" data-original-width="891" height="364" src="https://1.bp.blogspot.com/-BbfytXDKOH0/XQK4RjybDEI/AAAAAAAA39k/yOqioAmf7FYFe7mBhcx1StjoZYg8MNhxgCLcBGAs/s640/pan_starrs_16bao.png" width="640" /></a></div>
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<span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">It turns out, that this star is an object PanSTARRS has light curve data for, as we can find out by going to the <a href="https://catalogs.mast.stsci.edu/panstarrs/" target="_blank">PanSTARRS portal at MAST</a>. I downloaded the data, which is <a href="https://outerspace.stsci.edu/display/PANSTARRS/PS1+FAQ+-+Frequently+asked+questions#PS1FAQ-Frequentlyaskedquestions-WhatfiltersdidPS1use?" target="_blank">for 5 filters</a> <a href="https://arxiv.org/abs/1203.0297" target="_blank">(g,r,i,z,y)</a>, and which range from 481 nm in the visual, to 962 nm in the near infrared. Here are the five light curves, which run from June of 2009 to July of 2013 (<a href="https://github.com/pdcarr/2016BAO" target="_blank">R scripts available on github</a>):</span></span><br />
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<a href="https://1.bp.blogspot.com/-4VwBTTlIPis/XQPlwTbXoYI/AAAAAAAA4D0/y0UeeFDFC7QvMKuxeJhRNCWTI6b2PONuQCLcBGAs/s1600/PSF_flux_improved.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://1.bp.blogspot.com/-4VwBTTlIPis/XQPlwTbXoYI/AAAAAAAA4D0/y0UeeFDFC7QvMKuxeJhRNCWTI6b2PONuQCLcBGAs/s640/PSF_flux_improved.png" width="640" /></a></div>
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<span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">There is something weird going on with the data here. I don't know how to diagnose if this is a problem with PanSTARRS, or if the source is doing that. If we look more closely and just <a href="https://arxiv.org/abs/1203.0297" target="_blank">g and r bands</a>, we see big "dips" in r, but not in g. It's possible that we just don't have enough detections to tell.</span></span><br />
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<a href="https://1.bp.blogspot.com/-q2GUDF3MGxg/XQPmxL1W1WI/AAAAAAAA4EA/q2mXixjJPMsdVxPAa4xwHqaX7FwW056YgCLcBGAs/s1600/PSF_g_r.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://1.bp.blogspot.com/-q2GUDF3MGxg/XQPmxL1W1WI/AAAAAAAA4EA/q2mXixjJPMsdVxPAa4xwHqaX7FwW056YgCLcBGAs/s640/PSF_g_r.png" width="640" /></a></div>
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<span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">OK, so to sum up: big dips apparent in the Gaia data, uncertain in the PanSTARRS data, but maybe. The source is too faint for AAVSO, ASAS-SN, or the Harvard plates (DASCH). I'm not sure if there are any other places to find photometry. If you start overlaying catalogs in Aladin, you don't get far.</span></span><br />
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<span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">Here are some more facts I can find:</span></span><br />
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<li><span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">It's in <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=I/345/gaia2&-c=297.72692580626%2B23.55034634583&-c.rs=0.5" target="_blank">the Gaia DR2 catalog</a>, and has a parallax estimate of 0.2437 +/- 0.0358 mas. That puts it at about 13384 light years away - almost 10 times further than Boyajian's Star. The Gaia G magnitude is 14.4 at that distance, which makes it quite a bit brighter than Boyajian's Star, which is listed at a G magnitude of 11.8 (bigger magnitudes are dimmer).</span></span></li>
<li><span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;"><a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=I/345/gaia2&-c=297.72692580626%2B23.55034634583&-c.rs=0.5" target="_blank">The star has a proper motion solution as well</a>. All the surveys find it to be a star, including ALLWISE and <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/316/gps6&-c=314.599188%2B43.886531&-c.eq=J2000.000&-c.rs=0.5" target="_blank">UKIDSS</a>.</span></span></li>
<li><span style="font-family: "times" , "times new roman" , serif;"><span style="background-color: white; color: #333333;">It seems to be really red, and maybe even have an infrared excess. It's <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/328/allwise&-c=297.7269274%2B23.5503536&-c.eq=J2000.000&-c.rs=0.5" target="_blank">ALLWISE object number is </a></span></span><span style="color: #333333; font-family: "times" , "times new roman" , serif;"><a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/328/allwise&-c=297.7269274%2B23.5503536&-c.eq=J2000.000&-c.rs=0.5" target="_blank">J195054.46+233301.2</a>, and its W3 and W4 magnitudes (different IR bands, with W4 being much longer wavelength) are 9.946 and 8.591 respectively. That's a quie a difference in brightness between the two bands.</span></li>
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<span style="color: #333333; font-family: "times" , "times new roman" , serif;">So, you've probably figured out where I'm going with this: with its big, sharp dips (bigger than Boyajian's Star) that look possibly like transits, a steady brightness when not dipping, and an IR excess (something Boyajian's Star lacks), </span><span style="color: #333333; font-family: "times" , "times new roman" , serif;">is this a candidate for a megastructure star? </span></div>
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<span style="color: #333333; font-family: "times" , "times new roman" , serif;"><br /></span></div>
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<span style="color: #333333; font-family: "times" , "times new roman" , serif;">Well, there is still plenty of room for doubt. It might be a particularly large and hot Young Stellar Object (YSO). Stars like this are still forming planets, and there are big <a href="https://arxiv.org/abs/1605.03985" target="_blank">disks of dust orbiting around them that can cause an IR excess and deep dips</a>, although I have yet to find an example of a dip as large as 1.7 magnitudes, especially for a big star, like the dips we saw from Gaia in 2016. </span></div>
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<span style="color: #333333; font-family: "times" , "times new roman" , serif;">Without more information, we probably can't know much more. The star hasn't had much attention from professional astronomers, and is too faint for amateurs.</span></div>
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<span style="color: #333333; font-family: "times" , "times new roman" , serif;">We don't have high cadence photometry data for this star like we do from Kepler, but we will, later this year, have some high cadence data from TESS for about 2 months. Perhaps one of the dips will occur at that time, and we can see the what the profile matches, if anything.</span><br />
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<span style="color: #333333; font-family: "times" , "times new roman" , serif;">All <a href="https://github.com/pdcarr/2016BAO" target="_blank">the data I've downloaded is on github</a>.</span></div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-40894329712974651222019-02-11T14:14:00.001-05:002019-02-11T14:14:32.916-05:00KIC 8462852 Analysis - you can participate<div dir="ltr" style="text-align: left;" trbidi="on">
Tabby Boyajian <a href="https://www.wherestheflux.com/single-post/2018/12/04/2018-data-update-40n" target="_blank">has a new initiative</a> related to the analysis of light coming from the star known as Boyajian's Star that I've blogged about quite a bit here and spoken about over at <a href="https://wowsignapodcast.com/" target="_blank">the Wow! Signal</a>.<br />
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The new initiative is about making telescope images in various wavelength bands from <a href="https://lco.global/" target="_blank">the Las <table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-9LAtonbQfIM/XGHJflg7VJI/AAAAAAAA1ck/7MlCiXZyeasMdBoauT6yQHKkKsTOb0rIwCLcBGAs/s1600/dsc00499.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1067" data-original-width="1600" height="213" src="https://2.bp.blogspot.com/-9LAtonbQfIM/XGHJflg7VJI/AAAAAAAA1ck/7MlCiXZyeasMdBoauT6yQHKkKsTOb0rIwCLcBGAs/s320/dsc00499.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">One of the Las Cumbres Telescopes</td></tr>
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Cumbres Observatory</a> network available in a regular basis for community analysis. These images will be centered around <a href="https://old.reddit.com/r/KIC8462852/wiki/index" target="_blank">Boyajian's Star</a>.<br />
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Citizen scientists will crack open the images, analyze the variations in the star's brightness at different colors, and look for emerging trends. It's a great project for a science or math class, or anyone of any age or background interested in participating. All you need is a computer, an internet connection, and the willingness to learn. Help is available with every step of the process.<br />
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The best way to get started is to go on over to <a href="https://www.reddit.com/r/KIC8462852_Analysis" target="_blank">the subreddit set up for this purpose</a>, and ask your questions. <a href="https://www.reddit.com/r/KIC8462852_Analysis/comments/agn22u/getting_started_downloading_and_installing/" target="_blank">Download and install AstroImageJ</a>, grab the training images, follow the how-tos and other guidance we have published, and learn by doing. We are putting more information there almost daily, and we expect the first batch of images in about 3 weeks, weather permitting.<br />
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You will be participating in solving a scientific mystery. We don't know where <a href="http://www.wowsignalpodcast.com/2018/01/burst-25-elsie-paper.html" target="_blank">the very fine dust is coming from that is causing the deep dips in brightness Boyajian's Star</a>, and there is very likely other material involved that <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-6-not-glimmer-of-idea.html" target="_blank">we haven't yet got much of a clue about</a>. The way these kinds of mysteries are typically solved is through lots of persistent and consistent effort by lots of people. Why not you?</div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-14333874329568425242018-12-28T23:59:00.001-05:002018-12-28T23:59:47.014-05:00A quick note on Useful and Useless Things<div dir="ltr" style="text-align: left;" trbidi="on">
I have started <a href="https://www.youtube.com/playlist?list=PLexgPF2KNQqnrcaCfyBYQAa73da-oXDZA" target="_blank">a new video playlist about things I find useful</a>. If you are so inclined, I hope you'll give it a watch from time to time. Here's the first one.<br />
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-89355332496404985622018-01-16T15:05:00.002-05:002019-02-13T23:11:18.115-05:00More fun with Aladin - Gaia Alert Gaia18adn<div dir="ltr" style="text-align: left;" trbidi="on">
You've probably heard of the <a href="http://www.esa.int/Our_Activities/Space_Science/Gaia_overview" target="_blank">European Gaia mission</a>. This special purpose space telescope is tasked with measuring the precise positions and movements in the sky of about a billion sources. When its mission is complete, we will have a far larger and more accurate catalog of the distances to the stars in our part of the galaxy, as well as how they are moving with respect to us. To achieve this feat, it has to observe each source many times. In addition to precise locations, Gaia can also measure the brightness of astronomical sources, and this includes distant galaxies as well as stars. Gaia has spotted numerous supernovas in other galaxies, as well as a number of other "optical transients." A transient is either an object that appears out of nowhere like a supernova, or objects the brighten or dim dramatically.<br />
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When Gaia spots a transient, a <a href="http://gsaweb.ast.cam.ac.uk/alerts/home" target="_blank">photometric science alert</a> is issued, and there have been lots of these. From time to time I browse through them, looking for unusual ones. It's interesting to track down what is known about the source to see what I can learn.<br />
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The most recent one that caught my eye was <a href="http://gsaweb.ast.cam.ac.uk/alerts/alert/Gaia18adn/" target="_blank">Gaia18adn</a><span id="goog_806861813"></span><a href="https://www.blogger.com/"></a><span id="goog_806861814"></span>. You can tell by the first number that it was issued in 2018. This is described as a "red" object. It is close to the galactic plane and doesn't appear to be extended, which means it's probably a star. If we had a measurement of its proper motion, we could know for sure it's not a galaxy, but we don't have that yet. Its Gaia source ID is <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=I/337/gaia&-c=302.4374471726%2B35.9663810018&-c.rs=0.004" target="_blank">2059140431331158272</a>, if you're keeping score.<br />
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Here is its lightcurve as <a href="https://arxiv.org/abs/1611.02036" target="_blank">measured by Gaia</a> and plotted by me:<br />
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<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-hSPoGruboAY/Wl15NA4dKpI/AAAAAAAAoSU/OKRcCb3CxK4TOTeTz5IxvPvzwdiHOPfOQCLcBGAs/s1600/G18adn_lightcurve.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://1.bp.blogspot.com/-hSPoGruboAY/Wl15NA4dKpI/AAAAAAAAoSU/OKRcCb3CxK4TOTeTz5IxvPvzwdiHOPfOQCLcBGAs/s640/G18adn_lightcurve.png" width="640" /></a></td></tr>
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You can see that it dips a fair bit over a couple of years, then declines sharply in brightness for several hundred days. It's declined by about 1.5 magnitudes, which is short of winking out altogether, but is about a three quarters loss of luminosity. If it continues to diminish, that would be really intriguing.<br />
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So, let's get out <a href="http://aladin.u-strasbg.fr/" target="_blank">Aladin</a> again. It's had a major upgrade lately (Version 10.0 in use here) and I find it an improvement, although the number catalogs and images available in the hierarchical menu is daunting.<br />
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The right ascension/declination coordinates for the Gaia source are given as 302.43742, 35.96636. I overlay the color image made overlaying observations by the <a href="https://www.nasa.gov/mission_pages/WISE/main/index.html" target="_blank">Wide Field Infrared Survey</a> (WISE) space telescope, and the ALLWISE catalog there:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-CTkNrkdImZM/Wl172tRjuWI/AAAAAAAAoSk/ftu3gNluavgfE9eNOaA7mTlSi3L4BzfBACLcBGAs/s1600/wise_circle_g18adn.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="474" data-original-width="627" height="481" src="https://4.bp.blogspot.com/-CTkNrkdImZM/Wl172tRjuWI/AAAAAAAAoSk/ftu3gNluavgfE9eNOaA7mTlSi3L4BzfBACLcBGAs/s640/wise_circle_g18adn.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="font-size: 12.8px;">WISE color image and WISE catalog (red circles)</td></tr>
</tbody></table>
If you click on the red circle nearest the reticle, you get which ALLWISE catalog item it is: <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/311/wise&WISE===J200944.98%2B355759.1&-c=302.437431%2B35.966419&-c.eq=J2000.000&-c.rs=0.004" target="_blank">J200944.98+355759.1</a>. It's <a href="http://irsa.ipac.caltech.edu/applications/wise/#id=Hydra_wise_wise_1&DoSearch=true&schema=allsky-4band&intersect=CENTER&subsize=0.20&mcenter=mcen&band=1,2,3,4&dpLevel=3a&UserTargetWorldPt=302.43743;%2B35.96642;EQ_J2000&SimpleTargetPanel.field.resolvedBy=simbadthenned&coaddId=&projectId=wise&searchName=wise_1&startIdx=0&pageSize=0&shortDesc=Position&isBookmarkAble=true&isDrillDownRoot=true&isSearchResult=true" target="_blank">really bright in the W4 band</a>, which is the longest wavelength WISE band, and the contamination and confusion flags look good in this case.<br />
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So, a star declining rapidly in brightness that is bright in the IR - a Dyson swarm in the making? Please? Well, you know - extraordinary claims, yada, yada. We need a closer look.</div>
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The same star has also been tracked by ASAS-SN, which is a ground-based telescopic campaign focused on transients. Here is a plot of the ASAS-SN V band data for this star, which may have some of the same dips.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-KXEi_ozYDEY/Wl5a7gcMEeI/AAAAAAAAoUE/79PM9DIDRb8TZc1UkhBHH4w_RsGNEp4QwCLcBGAs/s1600/18adn_asassn.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://1.bp.blogspot.com/-KXEi_ozYDEY/Wl5a7gcMEeI/AAAAAAAAoUE/79PM9DIDRb8TZc1UkhBHH4w_RsGNEp4QwCLcBGAs/s640/18adn_asassn.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Gaia 18adn ASAS-SN observations</td></tr>
</tbody></table>
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So, it looks like an inconsistent story. Where is that deep decline near the end of the curve in the ASAS-SN data?<br />
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The answer appears to be that there is a lot going on between the Gaia observations. If I subtract a constant 5.2 from the Gaia data (blue circles), and overlay the last 300 or so days of the two plots, I get this:<br />
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<a href="https://1.bp.blogspot.com/-3xdoqED7TJQ/Wl5Vudi6caI/AAAAAAAAoT0/J7gfZNmhWSYy8ieEYedwvQMsg7qg4i8yQCLcBGAs/s1600/18adn_asassn_compare.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://1.bp.blogspot.com/-3xdoqED7TJQ/Wl5Vudi6caI/AAAAAAAAoT0/J7gfZNmhWSYy8ieEYedwvQMsg7qg4i8yQCLcBGAs/s640/18adn_asassn_compare.png" width="640" /></a></div>
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What looked like a smoothish declining trend in the Gaia data is now revealed as some highly variable photometric activity.<br />
<br class="Apple-interchange-newline" />
That suggests that it is a <a href="https://www.cfa.harvard.edu/rg/star_and_planet_formation/young_stellar_objects.html" target="_blank">Young Stellar Object</a>, or <a href="https://arxiv.org/abs/1605.03985" target="_blank">YSO</a>, and is actually more like I would expect a YSO to behave, since we don't expect smoothly varying dust concentrations blocking the star's light. As has been seen with other YSOs, there is a lot of fluctuation. This tends to predict that we should see the star mostly up around 12.7 V magnitude when the star becomes visible to ASAS-SN again in the Spring of 2018. So, probably not winking out.<br />
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YSOs typically have a lot of dust surrounding the star, soaking up the starlight and reradiating it in infrared, which would explain the strong signal in W4. Now, that dust will eventually get organized and the star will become more clearly visible.<br />
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It's also nice to zoom out on the WISE image:<br />
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<a href="https://1.bp.blogspot.com/-J6cFHeTD3_E/Wl2H0B6DzsI/AAAAAAAAoTI/Ys8-D32bly83O8lSzfbqtKiUKXPD-Q2xACLcBGAs/s1600/gaia18adn_wise_zoomout.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="474" data-original-width="627" height="482" src="https://1.bp.blogspot.com/-J6cFHeTD3_E/Wl2H0B6DzsI/AAAAAAAAoTI/Ys8-D32bly83O8lSzfbqtKiUKXPD-Q2xACLcBGAs/s640/gaia18adn_wise_zoomout.png" width="640" /></a></div>
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I'm just showing you that because I think it's pretty.<br />
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You can just start loading catalogs in Aladin to your heart's content to see if anything else is there. For example, there doesn't seem to be an X-ray source there. Here's an image from one X-ray survey:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-i-zi-kJvapk/Wl2DdnwgvzI/AAAAAAAAoS8/J4RZrhY-U1Uz1o64_W07vIwRdx4iRXHFACLcBGAs/s1600/no_x_ray.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="474" data-original-width="627" height="481" src="https://2.bp.blogspot.com/-i-zi-kJvapk/Wl2DdnwgvzI/AAAAAAAAoS8/J4RZrhY-U1Uz1o64_W07vIwRdx4iRXHFACLcBGAs/s640/no_x_ray.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">ROSAT all sky survey, 0.1 - 0.4 Kev</td></tr>
</tbody></table>
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There is radio energy in that region, but this is typical of the galactic plane. For example, here is the nearby Planck HFI color composite image:<br />
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<a href="https://2.bp.blogspot.com/--InQSOk-ZWQ/Wl2JECmEMTI/AAAAAAAAoTU/fx8OQwbkfHc7jrhVqJ57MJb7Ieg6jUk6QCLcBGAs/s1600/Planck.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="474" data-original-width="627" height="482" src="https://2.bp.blogspot.com/--InQSOk-ZWQ/Wl2JECmEMTI/AAAAAAAAoTU/fx8OQwbkfHc7jrhVqJ57MJb7Ieg6jUk6QCLcBGAs/s640/Planck.png" width="640" /></a></div>
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In my relatively brief search, I could find anything weird about this star. The only missing piece is that I would like to know more about how far away it is, and how fast it is moving across the sky. Still, from what I can tell it is very likely a YSO. </div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-80723126688901329342018-01-05T14:21:00.000-05:002019-02-13T23:10:38.258-05:00The Elsie Paper<div dir="ltr" style="text-align: left;" trbidi="on">
<b>Note</b>: <i>after this was nearly done, couple of people pointed out to me the simultaneous release of <a href="https://arxiv.org/abs/1801.00720" target="_blank">a preprint by Deeg+</a> that reaches essentially the same conclusion as <a href="https://arxiv.org/abs/1801.00732" target="_blank">the Boyajian+ paper</a>, but uses a different method, and covers all 4 2017 dips</i>.<br />
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This post is a slightly updated text version of <a href="http://www.wowsignalpodcast.com/2018/01/burst-25-elsie-paper.html" target="_blank">Wow! Signal Burst 25</a>, which was was being released on the 3rd of January 2018, almost simultaneously with a press release announcing <a href="https://arxiv.org/abs/1801.00732" target="_blank">a new paper on Tabby’s Star by Boyajian, et. al., titled <i>The First Post-Kepler Brightness Dips of KIC8462852 </i></a><br />
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<a href="https://disownedsky.blogspot.com/2017/11/im-still-perplexed-tabbys-star-update.html" target="_blank">In a previous post</a>, I went over the events of last summer and into the Fall of 2017. I recommend that one first if you are unfamiliar with those events, and also to <a href="https://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">Tabby's Star for the Perplexed</a>. We also had <a href="http://www.unseenpodcast.com/2017/10/episode-81-another-year-of-wtf-with-eva.html" target="_blank">a conversation with astrophysicist Eva Bodman on the Unseen Podcast in October 2017</a> in which we discussed recent developments.<br />
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<a name='more'></a><br /><br />
To provide a very quick summary there were 4 brightness dips observed from Boyajian’s Star over the summer, with increasing depth and duration. These were named, in order, Elsie, Celeste, Skara Brae, and Angkor. Following the Angkor dip, there was a prolonged period during which the star’s brightness increased, informally dubbed “the blip” - and now the blip may be repeating. In Burst 24 we also discussed the published evidence we had to date that whatever is causing both the dips and the long term dimming must have as a major component, very fine dust.<br />
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The new paper is about observations taken over that period of time in 2017, but is primarily focused on Elsie. Since no one knew at the time that there would be more dips after Elsie, a lot of resources were martialed to monitor that one dip.<br />
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The paper is in 5 Sections and an appendix. It discusses a large number of observations taken over the summer, including SETI observations, and discusses their implications for models explaining the star’s behavior. What I intend to do in this burst is briefly visit each section and explain what’s going on in more depth than you’ll get in a press release, but probably less than an undergraduate astrophysics class. I’ll try to explain a few concepts that are important to the paper, but I won’t cover every detail. Any mistakes or missions are my fault alone.<br />
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Also, note that at several points in this paper, papers currently in progress are mentioned. More information is coming. In particular, the infrared observations are still being written up. I hope there will be some interesting findings there.<br />
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Section 1</h3>
Let’s start with the Introduction. This goes over pretty much the same ground as <a href="https://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">covered in our previous posts addressing Tabby’s Star</a>. It begins with the Planethunters discovery of the oddities of this star based on the Kepler space telescope data, and takes us up to the start of Elsie, although some of the literature reviewed in this section was first released post-Elsie.<br />
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Section 2</h3>
Section 2 is the big section, covering photometry, infrared photometry, spectroscopy, polarimetry, and radio SETI observations. I’ll explain what each of those is when we get to it.<br />
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Let’s start with section 2.1, which is photometry.<br />
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<a href="https://community.dur.ac.uk/physics.astrolab/photometry_theory.html" target="_blank">Photometry</a> is a measurement of how the brightness of a star varies, and how this variation depends on which band of light wavelengths you use. The brightness in turn depends on a number of things, including how much <a href="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/dust.html" target="_blank">interstellar dust and gas</a> the light has to travel through to get to Earth. A graph of the measured brightness vs. time is called a light curve. The first part discusses the monitoring that was going on since 2016 using the crowdfunded <a href="https://lco.global/" target="_blank">Las Cumbres telescope network</a>. When photometry using the Las Cumbres network first noticed Elsie beginning on the 19th of May, a number of other telescopes joined in on the observations. Figure 1 in the paper shows Elsie light curves from 12 different observatories. These are all detailed in the Appendix. They all show the same basic shape for Elsie, but vary in depth depending on the color band of light observed.<br />
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Section 2.1.1 was one of the most interesting to me, because it describes the dips in more detail than we’ve seen before. For example, the paper notes the very shallow decline in brightness between between Celeste and Skara Brae - which I called DWAIN at the time (Dip Without an Interesting Name), although I have also thought could be interpreted as the long term dimming bottoming out. The paper leaves open the interpretation of DWAIN.<br />
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I am particularly intrigued by the third dip known as Skara Brae, and details on the “twinkle” event at the center of Skara Brae, which they describe as a very short duration dip (see Figure 3) that bounces to a higher brightness. They compare the twinkle to the Kepler Day 1540 dip, which does look similar, but they caution against reading too much into that. It’s still not clear to me how any model out there now is going to explain Skara Brae, but most likely I’m not applying enough imagination.<br />
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There is also some interesting discussion of the steepest dip, Angkor, and how brightness hovered just below normal before it fully recovered.<br />
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Section 2.2 - Spectroscopy - is what we’ve only had limited information about so far.<br />
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In photometry, we look at broad bands of color (or equivalently, wavelength) and measure the brightness of the star in that band. In spectroscopy, we are interested in a very detailed account of how the brightness varies with wavelength -its spectrum - since different substances either emit or absorb light at very specific wavelengths. Astronomers have been doing spectroscopy for generations, and can learn a great deal about a star from studying its spectrum, including how fast it is moving toward or away from Earth - also known as the radial velocity.<br />
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You might guess that because we are dividing the light up into many small pieces, we need a more powerful telescope to get good data, and you are correct. The big telescopes used for spectroscopy are far more expensive and harder to schedule, so we can’t just monitor the star all the time with spectroscopes. The smallest telescope detailed here was the 3 meter Shane telescope, and the other was the 10 meter Keck telescopes in Hawaii.<br />
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Although more details are forthcoming about the spectroscopy, one of the things discussed in the paper was an effort to measure any radial velocity difference between the dips and the times when there were no dips. Long story short, no statistically significant difference was found. We already knew from earlier observations that Boyajian’s Star did not have a close companion, and thi confirms it, although a big planet could be still be fairly close to the star.<br />
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Also, the team notes that the usual absorption lines you would expect to see from the interstellar medium are there, and they don’t detectably vary during the dips. It is suggested that we need to see a deeper dip in order to really measure this well.<br />
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The bottom line for spectroscopy - so far - is that nothing obviously strange happened to the star’s spectrum during the dips.<br />
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Section 2.3 is a short section about the photometry in infrared light taken by the NEOWISE space telescope. All we know is that no change in brightness during the dips was observed at all. Once again, we are told this is more information coming in two new papers.<br />
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Section 2.4 talks about polarimetry, or measurements of the polarization of light coming from the star. Essentially, the polarization observed is very probably due to interstellar dust and has nothing to do with the star or anything happening close to the star.<br />
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Section 2.5 describes radio SETI efforts during the dips. Here we are looking for very powerful, artificial radio signals coming from the star using the SETI Institute’s Allen Telescope Array in California. In the radio band that they searched, they found no such signals.We have discussed on this podcast before why this is not surprising, even if you think an ET civilization is operating near Tabby’s Star.<br />
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Section 3</h3>
Section 3 is analysis, and Section 3.1 is very important. The results are summarized in Figure 7 of the paper, which shows after some analysis of the photometry data, that there are distinct differences in the depths of the light curves at different color bands. Between the shortest and longest wavelength bands, the ratio of the dip depths is almost a factor of two - 1.94. The word astronomers will use for this color variation as that the dips are <i>chromatic</i>. That is very hard to explain with a solid object of any sort.<br />
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Section 3.2 takes the color ratios observed and uses this to perform a detailed analysis of the particle sizes that could be scattering the star’s light differently at different wavelengths. This gets into some detailed mineralogy that I won’t detail here.<br />
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A number of different minerals are considered, but all require that the particle sizes are much less than 1 micron, and optically thin. Optically thin, simply put, means that the light is shining through the material, and is not being so much blocked by it, but scattered. This sort of small dust particle can not orbit the star, because the star’s radiation pressure will blow it out of the system, so whatever is producing the dust is producing it more or less continually. This is one problem I have with the symmetry of the dips - I would expect the cloud of dust to look more like a comet’s tail. I suspect that what we are seeing isn’t just a transit signature, but a burst of dust production that corresponds with a transit.<br />
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Section 4</h3>
Section 4 is the Discussion Section, in which the team compares the new data to several models. They show, for example, that it’s hard if not impossible for a giant artificial megastructure to produce the kind of color variations seen (or just any very large opaque object). Just because we think that there is dust blocking the star doesn’t make it easy to figure out where that dust came from, though.<br />
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They lend some encouragement to a model that involves a lot of exocomets or dust-shrouded planetesimals - something has to be producing the dust after all, and they strongly hint that we would need target-of-opportunity time on the James Webb Space Telescope to really narrow down the parameters of such a model. This telescope, if we are lucky, will launch some time next year, although Boyajian’s star is not one of its early science objectives.<br />
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Also discussed is a simple model to determine whether stellar cool spots might be responsible for the Elsie family of dips. The result is a firm “maybe,” and they don’t rule out more complex models of how the star might be cooling or changing radius.What it will take to rule those models out isn’t clear to me.<br />
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They also caution against any assumption that the events seen to date are periodic with the information we have to date. It certainly seems to me that the system we are observing is evolving a great deal, and the recent “blips” throw a new wrinkle into that. Perhaps, they note, observations in June of 2019 might help us to see a repeat of the first big dip in the Kepler light curve.<br />
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Section 5</h3>
Section 5 is the conclusion section, and takes a look at the bigger picture. The use of crowdfunding is one element they highlight, and they summarize the key results, especially the fact that the 2017 dips were chromatic. Finally, they make the case for further monitoring over the long term. You can do something about that by going over to <a href="http://wherestheflux.com/">wherestheflux.com</a> and making a donation to pay for telescope time.<br />
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I have had some e-mails and other communications that worry that Alien Megastructures are now out the door because of the fine dust. As I’ve discussed before, there is a major problem with the classic sort of Dyson Swarm megastructure hypothesis for Boyajian’s Star that have nothing to do with the chromatic dimming - the constraints on excess infrared brightness that Dyson predicted in <a href="http://fermatslibrary.com/s/search-for-artificial-stellar-sources-of-infrared-radiation" target="_blank">his 1960 Science paper "Search for Artificial Stellar Sources of Infra-Red Radiation"</a>. These constraints get just a bit tighter now with the NEOWISE observations, although the details are in work. However, if ET is operating around this star, what are the chances they would be kicking up a considerable amount of fresh dust? What other observables might their activities have? I don’t have an answer to those questions, but I think they are intriguing questions, and I plan to look further into them<br />
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-84732767860976119482017-11-28T23:01:00.001-05:002019-02-13T23:12:03.845-05:00I'm still perplexed - Tabby's Star Update for November 2017<div dir="ltr" style="text-align: left;" trbidi="on">
<b><i>Update: 29 November 2017</i></b><br />
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I've been meaning to put out an update for the last several months, and just when I am poised to do so, something else happens. So, here it is is, and I may need another update soon. It' s been an eventful few months, and if you haven't been following closely, you may want to read this.
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<h2 style="line-height: 1.38; margin-bottom: 0pt; margin-top: 10pt; text-align: left;">
The tl;dr</h2>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span></div>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><i>Kickstarter-funded observations of the star by the Las Cumbres telescope network began in 2016. There was a Winter interruption when the star was too close to the sun, but observations resumed in the Spring. From about mid-2016 there was a prolonged dimming episode which I am tempted to assume was related to what followed. In May, we saw our first of four dips, during which the overall slow dimming stopped and turned into a slow brightening. After the last dip in mid September, the star brightened for about one month, levelled off in brightness, and lately has been slowly dimming again. There are some new preprints out that contain some interesting tidbits.</i></span><br />
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The Quiet, Slowly Dimming Period</h2>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Before the first dip in May of 2017, we already had strong reason to believe that the star had been slowly dimming for the better part of a year from the AAVSO data. I posted this tentative conclusion of 1-2% per year dimming in April of 2017. I compared this to the dimming Montet and Simon has mined out of the Kepler Full Field Image data (see Wow! Signal </span><a href="http://www.wowsignalpodcast.com/2016/08/3-episode-8-ben-montet-makes-star.html" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">Episode 33</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">), which was a precursor to a series of dips, and wondered if a dip might be coming soon. </span><br />
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<h2 style="text-align: left;">
The Sequence of Dips </h2>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Things started to get really interesting in Mid May of 2017, just as the Las Cumbres Observatory was getting into full swing monitoring the star.</span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
<br />
<h3 style="text-align: left;">
Elsie</h3>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">The first dip of 2017 started around the 18th of May 2017, and lasted for about 5 or 6 days, during which the star’s brightness declined more than 1%, and even closer to 2% at peak. 1% may not seem like much, but that is a measurable decline in flux and not something that is normally seen with main sequence stars like this, as we discussed in <a href="https://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">Tabby's Star for the Perplexed</a>. Also, 1% is way too big to be a transiting planet for a star this size. This dip was later named “Elsie” after a vote by the Kickstarter supporters.</span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Since no one knew whether there would be more dips or not, an Astronomer’s Telegram went out, and a number of astronomical instruments pointed at the star in those few days. We don’t have all the data made public yet, but we do know that this dip resulted in a slight reddening of the star - that is, the dip </span><a href="http://www.wherestheflux.com/single-post/2017/06/26/Dip-update-17n---dip2-and-data-update" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">was definitely deeper in blue light than in red</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">. This is strong evidence that whatever was blocking the star was not a single solid object, but had very fine dust as a major component. These dust particles would have to be well under 1 micron in size, which is typical of dust seen in the interstellar medium or comet dust, but such small particles in orbit around the star would not last long before the pressure of starlight (which exceeds the force of gravity) drove them away.</span><br />
<h3 style="text-align: left;">
</h3>
<h3 style="text-align: left;">
Celeste</h3>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">A </span><a href="http://www.wherestheflux.com/single-post/2017/06/15/Dip-update-9n" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">second dip started on the 11th of June</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">, and was eventually named </span><a href="http://www.wherestheflux.com/single-post/2017/06/25/Guest-post-from-astronomer-Angelle-Tanner" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">Celeste</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">. Celeste lasted about 2 weeks, and was also a bit more than a 1% drop in brightness. We don’t yet have a full report of the observations taken during Celeste, but so far, I don’t believe there was much difference from Elsie. </span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Following Celeste, there was as period during which the brightness of the star seemed unsettled. I called this DWAIN, but it wasn’t a dip. What we can see now in retrospect was the brightness of the star - neglecting the dips - was bottoming out.</span><br />
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</h3>
<h3 style="text-align: left;">
Skara Brae</h3>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">The third dip was, to my mind, the strangest. And began about the 2nd of August. This dip was named Skara Brae, and lasted about 16 days until </span><a href="http://www.wherestheflux.com/single-post/2017/08/18/Dip-update-61n" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">August 18th</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">. In addition to its duration (a typical planetary transit is well under 1 day), what makes Skara Brae stand out is its symmetry, the linear slopes of its sides, and a high degree of photometric activity in the exact center of the dip, when the brightness was briefly down 3%.</span><br />
<h3 style="text-align: left;">
</h3>
<h3 style="text-align: left;">
Angkor</h3>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">The fourth and largest dip - Angkor - started around the 28th of August, dipped to about 2%, and lasted until the 14th of September - the exact times when a dip starts and ends are a little fuzzy - so it lasted about as long as Skara Brae, and was deeper on average, although it seems to have been a bit more ragged and not quite as cleanly symmetrical - it seemed to bottom out (sharply, like Skara Brae) on around September 10th.</span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">One notable thing about Angkor is that it was the first dip that the AAVSO data clearly caught. This is probably because of its depth. </span><br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-Vl9zfv3z3lA/Wh7AhXlluDI/AAAAAAAAmlg/5JHWq43Uuy8jtGQT3xVQjL_C9tmqCaBaQCLcBGAs/s1600/09f35d_ffca127534f0471583850c37b021a010%257Emv2.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="451" data-original-width="630" height="456" src="https://3.bp.blogspot.com/-Vl9zfv3z3lA/Wh7AhXlluDI/AAAAAAAAmlg/5JHWq43Uuy8jtGQT3xVQjL_C9tmqCaBaQCLcBGAs/s640/09f35d_ffca127534f0471583850c37b021a010%257Emv2.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A recent LCO light curve from <a href="http://www.wherestheflux.com/">http://www.wherestheflux.com/</a></td></tr>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
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<h3 style="text-align: left;">
<span style="font-family: "times new roman";"><span style="white-space: pre-wrap;">The Post-Dip Brightening and Dimming Again</span></span></h3>
<br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">After Angkor, it became apparent that the star was brightening slowly in the shorter wavelength. In B band, this brightening may have been as much as 2% from the minimum between Celeste and Skara Brae. We don’t have as much data in the longer wavelength I band data from AAVSO, but the I band brightness appears to be roughly flat after Angkor. I say “appears” because the scatter in the I data is around 2%, so it will take a while to see a trend emerge.</span><br />
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">I would have enjoyed it if the star had just kept brightening for a long time, but in mid November, Bruce Gary noticed a rapid decrease in brightness over 1 day, and a slow decline thereafter, and for now we have seen the star give up about half of its brightness gain since Angkor.</span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
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<h2 style="text-align: left;">
<span style="font-family: "times new roman";"><span style="white-space: pre-wrap;">Some New Papers in Process Made Public</span></span></h2>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Scientific papers come out fast in preprint these days, as the recent flurry of papers addressing the hyperbolic asteroid Oumuamua made clear. This is partly because astronomers can reduce their data very rapidly, and also because they can collaborate electronically. This has also been happening with recent developments on Boyajian's Star.</span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">In August, a couple of new preprints came out, and both dealt with the long term dimming of the star. As always, there will be links in the show notes. They generally agreed that there had been a slow dimming trend since 2016, but the </span><a href="https://arxiv.org/abs/1708.07822" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">paper by Simon et. al.</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> dug up a 4000 day span of data from the All Sky Automated Survey, and found that there had also been two periods of brightening. This isn’t surprising that the star doesn’t just dim all the time, but no one had found an example until now. The </span><a href="https://arxiv.org/abs/1708.07556" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">second preprint, by Meng, et. al.,</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"> also looked closely at the recent slow dimming using data from the Swift space telescope as well as ground based observations. They found a reddening in the dimming which was different than reddening we see from interstellar medium, suggesting that whatever is causing the dimming is orbiting around the star.</span>
<span id="docs-internal-guid-face6c33-05a3-cd03-16b3-d37c29fa0b3d"></span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">In September, there was an <a href="https://arxiv.org/abs/1709.06061" target="_blank">interesting preprint by Steele, et. al.,</a> that looks at the polarization of light during the period of the dips. I'm not yet sure if these measurements constrain any hypotheses that much, but I'm glad someone took a look at it.</span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"><br /></span>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Another preprint, by Wyatt, et. al. published in October, looks at the Exocomet interpretation in terms of the Elsie dip. This paper revealed that there is infrared space telescope data from <a href="https://neowise.ipac.caltech.edu/" target="_blank">NEOWISE</a> (not yet <a href="http://irsa.ipac.caltech.edu/Missions/wise.html" target="_blank">made public</a>) during Elsie, and that no increase in emission was detected during Elsie. They give the integrated depth of Elsie as 6.5 %-days. Angkor and Skara Brae had much greater integrated depths, and so there would be more hope of detecting an infrared excess. If there are such data, they haven’t been released yet.</span>
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<br />
<h2 style="text-align: left;">
What We're Looking Forward to Now</h2>
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 12pt; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">As the star comes together with our sun, photometric observations from the ground will get harder to come by until early Spring of 2018. Only observers in the more northern latitudes will have a good look at it when the sun is down. We hope that some space-based observing time will be made available, as it was last Winter, so that we can keep monitoring for more dips.<br />
A lot of people think they know something about the periodicity of the dips, but this remains speculative until someone can clearly demonstrate at least <i>three</i> closely similar events with an even spacing between them. To me, the system is clearly evolving, and fine dust is blocking at least some of the flux, and this dust will not be in a periodic orbit - it must be produced afresh by something else that may or may not be doing so periodically.<br />
In the near term, we await a paper by Boyajian, et. al. that brings together all the observational data from the dips, or at least from Elsie. We have reason to believe that is in work, but it's likely be time consuming to get it right, and will be worth waiting for.</span></div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-61060904722919322092017-07-18T02:33:00.002-04:002018-05-23T23:01:45.974-04:00July 2017 Update on Tabby's Star<div dir="ltr" style="text-align: left;" trbidi="on">
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If you want to know what is going on day to day with Tabby's Star, then the site <a href="http://wherestheflux.com/" target="_blank">Where's The Flux</a> is an excellent resource. If you want to catch up on the basic info with sourced facts, you might want to check out <a href="https://www.reddit.com/r/KIC8462852/wiki/index" target="_blank">the Wiki on /r/kic8462852</a>. It includes a timeline of what has happened so far and a list of information sources - both the professional literature and more accessible materials as well.<br />
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In this post I'll try to create a bit more context without going overboard on the speculation. People love speculating on this star (<a href="https://www.reddit.com/r/KIC8462852/comments/6kokxc/id_almost_forgotten_about_this_in_all_the/?ref=share&ref_source=link" target="_blank">as do I</a>), but really very little of it is justified at this point. The hard work of observing and phenomenology has to take precedence. My main focus has been on figuring out the broad strokes of what it is we've been seeing since October of 2015 when this ordinary star suddenly became the focus of intense study.<br />
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<h3 style="text-align: left;">
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<h3 style="text-align: left;">
The Elsie Complex</h3>
As <a href="http://www.wowsignalpodcast.com/2017/06/burst-23-tabby-boyajian-talks-about-may.html" target="_blank">we documented earlier, in May of 2017 the star had its first real dip in brightness</a>, since dubbed "Elsie." In June, there was another dip, "Celeste," and that was shortly followed by another shallow dip of long duration, which does not yet have a name (let's call it "DWAIN," or Dip Without an Interesting Name).<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-_e9PPMAVDD4/WW5C8twQm_I/AAAAAAAAj6E/Gu3ftUOiSFUFQ081_silqsOSjzTdyTp3ACLcBGAs/s1600/Elsie_Celeste_DWAIN_2.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="750" data-original-width="1050" height="456" src="https://2.bp.blogspot.com/-_e9PPMAVDD4/WW5C8twQm_I/AAAAAAAAj6E/Gu3ftUOiSFUFQ081_silqsOSjzTdyTp3ACLcBGAs/s640/Elsie_Celeste_DWAIN_2.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Elsie, Celeste, and DWAIN, which continues. Based on <a href="https://lco.global/" target="_blank">LCO</a> photometry data</td></tr>
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DWAIN was only about 0.5% below normal, but went on for a long time - at least two weeks - and we're still not sure it's over. <a href="https://arxiv.org/abs/1509.03622" target="_blank">The WTF paper</a> reported two 0.5% dips (1 and 2) as observed by Kepler, and another one of 0.4% (dip 6). However, none of them lasted as long as DWAIN. Here's what Dip 1 looked like - about 2-3 days in duration. Note the abrupt entry, the peaked minimum and smooth, gradual exit. This sure doesn't look like a planet, where we'd expect a fair bit of symmetry and a flatter bottom.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-COE4qW9JU5M/WW2qEumbg3I/AAAAAAAAj5Q/fZupO1VL2NcV_ly4LaRHcI1oRmVeVZlKQCLcBGAs/s1600/download.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="420" data-original-width="720" height="371" src="https://1.bp.blogspot.com/-COE4qW9JU5M/WW2qEumbg3I/AAAAAAAAj5Q/fZupO1VL2NcV_ly4LaRHcI1oRmVeVZlKQCLcBGAs/s640/download.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Dip 1 from the <a href="https://archive.stsci.edu/kepler/data_search/search.php?target=KIC+8462852&action=Search&resolver=SIMBAD&radius=3.0&outputformat=HTML_Table&max_records=5001&ordercolumn1=ang_sep&ordercolumn2=sci_ra" target="_blank">Kepler Space Telescope data</a><br />
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<div style="text-align: left;">
<span style="font-size: small;">Dip 4 (D425) looks more like what we've been seeing lately. Apparently chaotic fluctuation with small dips. It was about a year after dip 4 that we see anything else in the Kepler data. Now, the current complex started about 2640 days after Dip 4, so <i>if</i> it's a repeat, the represents a period of about 7.2 years (or possibly half that, since we would have missed out on the last repeat in that case).</span></div>
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<a href="https://1.bp.blogspot.com/-puGDNYt8w84/WW55L_nG5CI/AAAAAAAAj6U/h2oognbKo0Uj7GliIDgU4dUN_CYNfcV-QCLcBGAs/s1600/dip4_chaos.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="420" data-original-width="720" height="372" src="https://1.bp.blogspot.com/-puGDNYt8w84/WW55L_nG5CI/AAAAAAAAj6U/h2oognbKo0Uj7GliIDgU4dUN_CYNfcV-QCLcBGAs/s640/dip4_chaos.png" width="640" /></a></div>
Dip 4 (0.2%) from the Kepler Space Telescope Data<br />
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<span style="font-size: small;">DWAIN doesn't look like a planet. In order to be a planet, to last this long it would have to be a planet far from the star with a really long period, so we would have to hit both the geometric and temporal lotteries to see it.</span><br />
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<h3>
<span style="font-size: small;">So, What is the best Analog?</span></h3>
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<span style="font-size: small;">Maybe there isn't a good analog in the <a href="https://archive.stsci.edu/kepler/preview.php?type=lc&dsn=KPLR008462852-2012179063303" target="_blank">Kepler light curve</a>, but we should keep the long term dimming in mind, especially what <a href="https://arxiv.org/abs/1608.01316" target="_blank">Montet and Simon derived</a> from the Full Frame Images. I have plotted their data below marking a couple of key dip events, using my own spline fit showing a steeper decline just after Day 1000:</span></div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td><a href="https://2.bp.blogspot.com/-mtFSHV652j4/WW_Q_89CPUI/AAAAAAAAj9g/8fJzaw_j9vwup3CewOcnav5_G9kTGQDuQCLcBGAs/s1600/Annotated_Montet.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://2.bp.blogspot.com/-mtFSHV652j4/WW_Q_89CPUI/AAAAAAAAj9g/8fJzaw_j9vwup3CewOcnav5_G9kTGQDuQCLcBGAs/s640/Annotated_Montet.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="font-size: 12.8px;">FFI Data showing dimming during Kepler Mission</td></tr>
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<span style="font-size: small;">Note that after about 200 days of decline there is a small dip and a period of chaotic, shallow fluctuations:</span><br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td><a href="https://2.bp.blogspot.com/-uGMZ72ZsyXg/WW_Q9B1JG1I/AAAAAAAAj9c/Dhfe6NqNXw0feD9KZXbtWD2zsLBEMZblQCLcBGAs/s1600/D1200.png" imageanchor="1" style="font-size: 12.8px; margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1001" data-original-width="1600" height="400" src="https://2.bp.blogspot.com/-uGMZ72ZsyXg/WW_Q9B1JG1I/AAAAAAAAj9c/Dhfe6NqNXw0feD9KZXbtWD2zsLBEMZblQCLcBGAs/s640/D1200.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="font-size: 12.8px;">D1200 Dip from Kepler PDCSAP data with some quality flagged points removed</td></tr>
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<span style="font-size: small;">The actual dip was at day 1206. So, if this is an analog, the dimming should continue for a while longer after being masked by the fluctuations, then level off before the next big event, about 300 days away from May 2017, or some time in March 2018.</span><br />
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<h3>
<span style="font-size: small;">The Long Term Dimming, Further Updated</span></h3>
<div>
<span style="font-size: small;">I had a look at the latest <a href="http://www.astronomy.ohio-state.edu/~assassin/index.shtml" target="_blank">ASASSN sky patrol</a> data. Ohio State's ASASSN is a supernova hunting project using small telescopes covering as much of the sky as possible. They don't specialize in precision photometry (you don't need to to tell a supernova has popped off), but they have taken some photometric data on KIC 8462852. This is <a href="https://github.com/pdcarr/Boyajians_R" target="_blank">on github</a> if you want to have a look at it yourself, or you can go <a href="https://asas-sn.osu.edu/" target="_blank">straight to the source</a>.</span></div>
<div>
<span style="font-size: small;"><br /></span></div>
<div>
<span style="font-size: small;">Although ASASSN seems to be biased a bit dim with respect to AAVSO, their data do show a similar pattern, although because of their southern locations their winter gap is fairly long. Their data was fairly flat until late in 2016, then dimmed a bit until recently. </span></div>
<div>
<span style="font-size: small;"><br /></span></div>
<div>
<span style="font-size: small;">The spline fit shown here an contains a recent upward trend, but I'm not sure this isn't just chasing a couple of bright points.</span></div>
<div>
<span style="font-size: small;"><br /></span></div>
</div>
</td></tr>
</tbody></table>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td><a href="https://2.bp.blogspot.com/-Ju_oYDT0PGo/WW7wanMLX9I/AAAAAAAAj7o/cLIKNU4fPKocd-OpL6N0kEr6ziSPnMIkwCLcBGAs/s1600/ASASSN.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1001" data-original-width="1600" height="400" src="https://2.bp.blogspot.com/-Ju_oYDT0PGo/WW7wanMLX9I/AAAAAAAAj7o/cLIKNU4fPKocd-OpL6N0kEr6ziSPnMIkwCLcBGAs/s640/ASASSN.png" width="640" /></a></td></tr>
<tr><td class="tr-caption"><span style="font-size: 12.8px;">Ohio State ASASSN data on KIC 8462852</span><br />
<br /></td></tr>
</tbody></table>
<span style="font-size: small;">Compare this to the latest AAVSO data (with better coverage across the winter gap): </span><br />
<div style="text-align: left;">
<span style="font-size: small;"><br /></span></div>
<div style="text-align: left;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td><a href="https://3.bp.blogspot.com/-xzzN-OgkusE/WW7yyoi45VI/AAAAAAAAj7s/aLOeDeL2Frc9thXstdRxyHDaMBgsp1_8ACLcBGAs/s1600/latest_V.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="1050" data-original-width="1050" height="640" src="https://3.bp.blogspot.com/-xzzN-OgkusE/WW7yyoi45VI/AAAAAAAAj7s/aLOeDeL2Frc9thXstdRxyHDaMBgsp1_8ACLcBGAs/s640/latest_V.png" width="640" /></a></td></tr>
<tr><td class="tr-caption"><span style="font-size: 12.8px;">AAVSO V band data fit with same spline algorithm</span></td></tr>
</tbody></table>
<br />
<div style="text-align: left;">
<span style="font-size: small;">So, although it's just above the noise, there does seem to be some corroboration that there was about 200-300 days of dimming at a level of about 2% per year before the current complex of small dips.</span><br />
<span style="font-size: small;"><br /></span>
<span style="font-size: small;">It's hard to tell for sure, but it appears that the dimming we saw in the winter and spring of 2017 has stopped. It may also be continuing, but there is too much activity to clearly discern it over the last two months. Various dimming models are in play, and telling them apart is tricky, but the null hypothesis seems to be hanging by a thread.</span></div>
<h3 style="text-align: left;">
<span style="font-size: small;">What to Expect Soon </span></h3>
<br />
I understand that Tabby and her team are working on a paper documenting the Elsie observations. We know there were IR and spectral observations at the minimum. I'm looking forward to the preprint, but it will take a while longer. Whether I undertake the exercise of unpacking that paper here will depend in how much content is there.<br />
<br />
<br /></div>
</div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-17632806940217879492017-06-29T23:25:00.001-04:002019-02-13T23:12:57.692-05:00More on the AAVSO trends for Boyajian's Star<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="https://disownedsky.blogspot.com/2017/04/a-conclusive-non-conclusion-about.html" target="_blank">My earlier post on the dimming</a> of KIC 8462852 that might be observable in the AAVSO photometry was looking for a single trend line, which seemed to be just observable above the noise. I hedge there, because there are always assumptions not far below the surface that might spoil the result. The human brain and randomness are old enemies, and often when we want to see a pattern, it's just nature playing tricks on us.<br />
<br />
<a name='more'></a><br /><br />
<br />
As more and more data came in, my visual impression of the data suggested to me that the light curve was fairly flat for the first few hundred days after AAVSO started taking data in 2015, and then sloped downward for about 100 or more days. <a href="http://www.wowsignalpodcast.com/2017/06/burst-23-tabby-boyajian-talks-about-may.html" target="_blank">In May 2017, we had a small dip</a>, and this month (June of 2017) we've had another shallow but prolonged dip:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-KzYMUFv5LoU/WVWthJk0xGI/AAAAAAAAjnM/Mq5HvKt-7BgvCIHtJnDGmPPbzr5D06yrwCLcBGAs/s1600/another_dip_qm.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="750" data-original-width="1050" height="457" src="https://3.bp.blogspot.com/-KzYMUFv5LoU/WVWthJk0xGI/AAAAAAAAjnM/Mq5HvKt-7BgvCIHtJnDGmPPbzr5D06yrwCLcBGAs/s640/another_dip_qm.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Plot by Tabetha Boyajian of the May and June 2017 dips</td></tr>
</tbody></table>
These dips are really below the AAVSO noise level and are just barely discernible in their data if we hold our breath and look cross-eyed at their light curves:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-b9ql4Z_jhy8/WVW62HsJzUI/AAAAAAAAjnc/p8ANjEmb0E0xRqCWD_MGEqZOjAcXZOlDACLcBGAs/s1600/29Jun17_BV_19ObsEnsemble.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="798" data-original-width="1506" height="338" src="https://2.bp.blogspot.com/-b9ql4Z_jhy8/WVW62HsJzUI/AAAAAAAAjnc/p8ANjEmb0E0xRqCWD_MGEqZOjAcXZOlDACLcBGAs/s640/29Jun17_BV_19ObsEnsemble.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">AAVSO data plotted at times of two dips</td></tr>
</tbody></table>
This plot of the "V" and "B" bands from the AAVSO data (averaged into 1 day bins for each of the 19 observers used), shows just what I mean. A 1% or 2% dip is just too subtle. As I write this (29 June 2017), it's not clear that the second dip is over yet. The black line drawn through the points is the R script's best effort at fitting <a href="https://en.wikipedia.org/wiki/Multivariate_adaptive_regression_splines" target="_blank">a linear spline</a> through the points while trying not to overfit - i.e. trying not to chase noise. The two red dotted lines represent the 18th of May and 11th of June 2017 - about when each dip started.<br />
<br />
However, it is possible to see long term trends. Here's what happens when we ask the the linear spline algorithm (called <i>earth</i>()) to limit the wiggles in the fit and just look for the big trends with the same 19 AAVSO observers.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-WGdkMWLK3Hk/WVXARMBfFfI/AAAAAAAAjns/qML2tgrRm84ddFu3gCDrT0Q9Ocv-2OI7ACLcBGAs/s1600/VB_pruned.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="798" data-original-width="1506" height="338" src="https://1.bp.blogspot.com/-WGdkMWLK3Hk/WVXARMBfFfI/AAAAAAAAjns/qML2tgrRm84ddFu3gCDrT0Q9Ocv-2OI7ACLcBGAs/s640/VB_pruned.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Plot over 638 days of AAVSO B and V data + pruned earth() spline fit</td></tr>
</tbody></table>
You can see a clear dimming trend. We have the most data in "V" band, and you can see there the curve is flat for about 286 days (early August 2016), when it turns downward at a rate of almost 3% per year (0.028 magnitudes/year). Even by eye, the trend appears to be unmistakable. In "B" the turning point seems to be coming a bit earlier, but the rate of decline is similar - about 2% per year. The trends in "R" data are similar. This is not that different from what <a href="http://www.wowsignalpodcast.com/2016/08/3-episode-8-ben-montet-makes-star.html" target="_blank">Montet and Simon saw in the Kepler Full Frame images</a>, just before the big series of dips in the stars light curve near the end of the Kepler primary mission.<br />
<br />
So, the notion that the long term dimming and the dips are related may be true, but the long term dimming isn't a constant. there may be long periods when the lightcurve is flat. I have a sense we're about to find out.<br />
<br />
All my data and scripts are <a href="https://github.com/pdcarr/Boyajians_R" target="_blank">on github</a>. Feel free to have a look and reach your own conclusions.</div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-18217279169991396832017-04-04T17:08:00.001-04:002017-04-19T11:26:10.529-04:00A conclusive non-conclusion about dimming in the AAVSO data<div dir="ltr" style="text-align: left;" trbidi="on">
I'm spending too much time on this, so will have to bring it to a close until the summer's observing is done.<br />
<br />
I took one more look at the <a href="http://aavso.org/" target="_blank">AAVSO</a> data, this time doing something called binning, <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-6-not-glimmer-of-idea.html" target="_blank">similar to what Brad Schaefer did with the DASCH data </a>in his paper on dimming in the historic photographic plates. Binning takes several observations within a defined time period and averages them before attempting to fit a model to them. In this case, <a href="https://en.wikipedia.org/wiki/Linear_regression" target="_blank">the model is a simple straight line</a>. This has the effect of giving each time period an equal "vote" in the best fit to the model, even if there is much less data in one time period than another. In the case of the AAVSO data, some observers would report many observations over a short period of time, which tended to overweight their observations. Binning mitigates that.<br />
<br />
Of course, you have to decide what period of time you will use for binning the roughly 500 day span we have so far. I arbitrarily picked 10 days, and averaged the observations for each observer over that time period. There were 47 AAVSO observers in all whose measurements survived the filtering process in the "V" passband. There were 48 observers, but I identified one who temporarily had apparent problems with respect to the others, so was filtered out to make it simple.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-pfyagLDN4hw/WOQE6IswWWI/AAAAAAAAiT4/Ul8gcfus9TQCQ-lvDShIVkApe2JKQGKMwCLcB/s1600/binned_V_10days.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://1.bp.blogspot.com/-pfyagLDN4hw/WOQE6IswWWI/AAAAAAAAiT4/Ul8gcfus9TQCQ-lvDShIVkApe2JKQGKMwCLcB/s640/binned_V_10days.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-size: small;"><b>The V Band Fit with 10 day binning</b></span></td></tr>
</tbody></table>
<br />
<a name='more'></a><br /><br />
While there is a dimming trend you can pick out of the binned data, the statistical significance is unimpressive. It's not a slam dunk. The dimming shown here is about 0.68 magnitudes per century, or about 0.6% per year. It could be real, but as you can see, it's small with respect to the scatter in the data. Here's what you get when you go to 50 day bins with the same 47 observers:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-FgsRvHHjNw4/WOQJUklhlJI/AAAAAAAAiUE/UIJz160FbsIvOdwkMhYHDHgeabPkzLcYgCLcB/s1600/aavso_50d_bins.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://1.bp.blogspot.com/-FgsRvHHjNw4/WOQJUklhlJI/AAAAAAAAiUE/UIJz160FbsIvOdwkMhYHDHgeabPkzLcYgCLcB/s640/aavso_50d_bins.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-size: small;"><b>The V data with 50 day binning</b></span></td></tr>
</tbody></table>
The result is roughly the same, but the dimming is a bit higher: about 0.9 magnitudes per century. The other bands I looked at (I,R, and B) have fewer observations, and binning made the results statistically insignificant.<br />
<br />
I will content myself to wait another 200 days or so to see if this is consistent. There are a couple of reason for this:<br />
<br />
<ol style="text-align: left;">
<li>There is plenty of reason to suspect that a linear dimming is too simple. It could stop for a while, or even reverse. We just don't know what is going on in any detail, and there is no physics in a linear fit. It's still possible that no dimming has been going on lately.</li>
<li>We might be fooled by uneven noise and biases, or what is called "systematics" in the data. Data over a longer time span can help us sort these out.</li>
</ol>
<div>
So, stay tuned. If you have your own analysis, <a href="https://www.reddit.com/r/KIC8462852/" target="_blank">come on over to Reddit</a> and share it with us.</div>
<div>
<br /></div>
<div>
Here's <a href="https://drive.google.com/file/d/0B_LvagsQCx-cMWY4TzZBTFg5Rms/view?usp=sharing" target="_blank">the new script</a>.</div>
</div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-5357414472393045332017-03-31T23:49:00.002-04:002017-04-19T11:26:43.058-04:00Brute Force and The AAVSO Data on Boyajian's Star<div dir="ltr" style="text-align: left;" trbidi="on">
We have more than 500 days span of data from the <a href="http://aavso.org/" target="_blank">AAVSO</a> data on <a href="http://www.wowsignalpodcast.com/2016/03/burst-13-tabbys-star-for-perplexed-part.html" target="_blank">Boyajian's star</a> now. I thought it might be worth a closer look to see if any of the secular dimming seen by either <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-6-not-glimmer-of-idea.html" target="_blank">Schaefer</a> in the archival plates or <a href="http://www.wowsignalpodcast.com/2016/08/3-episode-8-ben-montet-makes-star.html" target="_blank">Montent and Simon in the Kepler full frame</a> images might still be going on.<br />
<br />
I am not a world class statistician, but sometimes a naive approach is interesting if we employ standard method knowing that our the systematics in the data are not well characterized yet.<br />
<br />
<h3 style="text-align: left;">
A little background information</h3>
<br />
So, a brief explanation of <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-5-catching-tabbys-star.html" target="_blank">what the AAVSO does</a>. Many of their members have equipped their telescopes with special electrically cooled digital cameras and optical filters that together can measure the brightness of a star in a particular color, or band, of light with respect to standard comparison stars. The colors we concern ourselves with right now are known as Blue, Visual, Red, and Infrared, or B,V, R and I for short.<br />
<br />
Over many decades, the AAVSO has done a great deal of careful work finding and observing comparison stars, which are in turn compared to each other. Each observer procures his or her own equipment, pays for access to training materials, and is responsible for making sure their gear is in good working order. They are supplied with AAVSO software that turns the digital counts on the cameras into a brightness, or as it is known, a magnitude.<br />
<br />
There are really only two things you need to know about magnitude to avoid being confused with what is to come. Some of it is historical accident, but it still makes sense in a way - unlike English spelling, which is all historical accident and little of it makes sense anymore:<br />
<br />
<ol style="text-align: left;">
<li>A higher magnitude means the source is dimmer. The brightest things in the sky have a <i>negative</i> magnitude, and the dimmest thing you can see with your naked eye on a dark, moonless night is around magnitude 6. This is why the Y axis of the points you will see seems to be upside down, with the higher numbers lower on the Y axis.</li>
<li>A small difference in magnitude is a big difference in brightness, because the scale is <a href="https://en.wikipedia.org/wiki/Logarithmic_scale" target="_blank">logarithmic</a>. This actually makes sense, since the brightness of astronomical objects varies over a huge range. A decrease in brightness by a factor of 100 is 5 magnitudes.</li>
</ol>
<h3 style="text-align: left;">
The AAVSO Data so Far</h3>
<div>
I want to start with spoilers. No one should get too excited about this yet. We need more data taken over a longer time span to confirm that the Schaefer dimming is still going on. There are several possibilities left standing, including that there is no dimming going on, although my unconfirmed hunch is that there is some dimming taking place. Permit me to explain.<br />
<br />
<a name='more'></a><br /></div>
<div>
<br /></div>
<div>
The AAVSO observers all deserve kudos for staying up late to snag a few measurements of Boyajian's star when they could. I've little doubt that each one did the best possible job with the equipment and observing conditions that they had.</div>
<div>
<br /></div>
<div>
<a href="http://aavso.org/" target="_blank">The AAVSO</a> started observing Boyajian's Star around October 2015, and have observed it almost every night they could except when the sun was too close in the sky to get good data - mostly in January and February. February 2016 was a washout, but a better effort was made in February 2017. None of the big dips observed by the Kepler space telescope have yet been seen in the AAVSO data, but that's not the only interesting thing, as we have documented.</div>
<div>
<br /></div>
<div>
I thought I would try using some fairly powerful tools in a naive way. I took all the AAVSO data up until 28 March of 2017. That's roughly 500 days, and a considerable number of observers, mostly in North America and Europe (the first "A" in AAVSO stands for American, but it's totally international now). It turns out that there are more than 30,000 valid observations of just this one star to date, and almost every day more are added. Most of them are I, R, B, and V bands as discussed above.</div>
<div>
<br /></div>
<div>
Let's focus on the "B" or blue color band for now, since that is what Schaefer was looking at. Astronomers actually call this Johnson Blue, but let's not get lost in those nuances. It represents shorter wavelengths of visible light than V, R or I. </div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-Yav23f6rBu8/WN8UV-tAEBI/AAAAAAAAiTQ/mneCQmFEHTcN2_Y22Tn4Sm6g02SuzJG9wCLcB/s1600/UBVRIpassbands.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="245" src="https://4.bp.blogspot.com/-Yav23f6rBu8/WN8UV-tAEBI/AAAAAAAAiTQ/mneCQmFEHTcN2_Y22Tn4Sm6g02SuzJG9wCLcB/s400/UBVRIpassbands.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The passbands for the various standard filters</td></tr>
</tbody></table>
OK, so let's start with only those "B" observations (2279 in all) that were taken at a reasonable angle above the horizon. in the the plot that follows, the blue points are the observation we are using, the black ones are the ones that were taken out, either because the "Airmass" was too high, or not reported:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-aQclqdu4Vmw/WN8YLBFlqrI/AAAAAAAAiTU/NWi3NLkn7tYt3tafwxXaGqOics8Be2kbwCLcB/s1600/Airmesslt2point9.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://4.bp.blogspot.com/-aQclqdu4Vmw/WN8YLBFlqrI/AAAAAAAAiTU/NWi3NLkn7tYt3tafwxXaGqOics8Be2kbwCLcB/s640/Airmesslt2point9.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-size: small;">The best fit to the selected B band data</span></td></tr>
</tbody></table>
<br />
You will see a line drawn through the data that is definitely trending down. In fact it is trending down at 1.75 magnitudes per century, which is much higher than the Montet/Simon dimming (about 0.6 magnitudes/century) or the Schaefer dimming (0.165 magnitudes per century). Should we believe this?<br />
<br />
Maybe not. One way to test the result is to fool around with the data. What if we didn't filter out so many points, and allowed any air mass, or even observations with no reported airmass? Easily done, and now there are more than twice as many "B" observations, 4648 in all:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-LUVIqvfpBUs/WN8b02RnS9I/AAAAAAAAiTY/1H8Z5LDe3LMdaFQ13Zq7vwUfgZh08W-yACLcB/s1600/aavos_28Mar2017_any_airmass.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://1.bp.blogspot.com/-LUVIqvfpBUs/WN8b02RnS9I/AAAAAAAAiTY/1H8Z5LDe3LMdaFQ13Zq7vwUfgZh08W-yACLcB/s640/aavos_28Mar2017_any_airmass.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-size: small;">The AAVSO B data with any air mass allowed</span></td></tr>
</tbody></table>
You can easily see from this that the slope reverses, and it's now getting brighter at almost 0.9 magnitudes per century. Both of these things can't be happening, so the result is too sensitive to the data allowed. There is more than one way to interpret this result, but to me the most likely is that we just haven't been observing long enough. Let's try one more experiment more, and eliminate the observations of one observer. Not to single anyone out, but I think the result is interesting:<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-Q0o8MuWq4po/WN8efTbrB2I/AAAAAAAAiTc/jwS-LMUo3XsRr1Ezte7SMVbyjFPc1B2FQCLcB/s1600/noFJQ_experiment.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://1.bp.blogspot.com/-Q0o8MuWq4po/WN8efTbrB2I/AAAAAAAAiTc/jwS-LMUo3XsRr1Ezte7SMVbyjFPc1B2FQCLcB/s640/noFJQ_experiment.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-size: small;">Any air mass, allowed, but one observer excluded.</span></td></tr>
</tbody></table>
<br />
What happens here is that the fit flips again from brightening to dimming at 1 magnitude per century! This is just one observer of many, and one who did all their observing over a span of 40 days, with what appears to be unusually large scatter over each session. However, it's a lot of points, and the linear regression algorithm in question thinks the more the merrier.<br />
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One could easily interpret the above as that the star is dimming anomalously fast in B, if we just ignore a small subset of observations. Not so fast. I want to know why the solution, using the <a href="https://stat.ethz.ch/R-manual/R-devel/library/stats/html/lm.html" target="_blank">lm() function</a> in <a href="https://cran.r-project.org/" target="_blank">the R statistical package</a>, is so delicate to the inclusion or exclusion of a single observer. It tells me that the problem is something bigger than one observer's telescope. Maybe, given the uncertainty inherent in the AAVSO data, the time span just isn't long enough. My hunch is that the star is dimming in B, but not as much as I'm seeing right now. I don't think a definitive conclusion is justified yet.<br />
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Stay tuned. We're going to put this all to the test as the time span lengthens. Give it a few hundred more days.<br />
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You can get <a href="https://drive.google.com/file/d/0B_LvagsQCx-cUTZTaHlSZW5fUXM/view?usp=sharing" target="_blank">my .R script here</a>, the <a href="https://drive.google.com/file/d/0B_LvagsQCx-cVy1EMWRUblJPTlU/view?usp=sharing" target="_blank">essential subroutines here</a>, and <a href="https://drive.google.com/file/d/0B_LvagsQCx-cN3FHaHhNLXdHZXc/view?usp=sharing" target="_blank">the data through 28 March here</a>. Try it yourself.<br />
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-3671206387020748432016-12-02T16:57:00.000-05:002016-12-08T12:19:35.772-05:00The Absolute, Definitive Truth About Alien Megastructures<div dir="ltr" style="text-align: left;" trbidi="on">
The title of this post is a joke, or taken literally, an outright lie. The only definitive truth is that no one knows if anyone has ever built a megastructure, or even if they would if they could. I have persistent doubts if such things exist anywhere in the universe, but I can't yet tell you if such doubts are reasonable.<br />
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<i>Update 8 December 2016</i><span style="font-weight: normal;">: I left out one type of motivation for building a megastructure - planetary climate control. Although these "Dyson Dots" would be relatively small, they might be detectable for transiting planets. I need to run the numbers...</span></div>
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The Usual Disclaimer</h3>
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So, we're going to be speculative here yet again, and very probably wrong. I won't be able to cite many facts, so if that is the sort of thing you like to read, perhaps now would be a good time to hit the back button.<br />
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But I'm Completely Serious</h3>
We are interested in the conjectured alien megastructures because we might have a chance to observe them with technology we have or could well have in the near future. These structures would be bigger than planets (my definition), and since we can observe planets about other stars, we might well be able to observe these things, and so looking for them is a kind of SETI. <a href="https://disownedsky.blogspot.com/2013/07/why-search.html" target="_blank">I've written before about why I think SETI is worthwhile</a>.<br />
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The Null Hypothesis</h3>
<a href="http://astro.psu.edu/people/jtw13" target="_blank"><br /></a>
<a href="http://astro.psu.edu/people/jtw13" target="_blank">Jason</a> Wright at Penn State has led a group that has gone looking for megastructures from their waste heat, called <a href="http://www.centauri-dreams.org/?p=29942" target="_blank">Glimpsing Heat from Alien Technologies</a>, or GHAT. They have mined data from infrared surveys like <a href="http://www.ipac.caltech.edu/2mass/" target="_blank">2MASS</a> and <a href="http://www.jpl.nasa.gov/wise/" target="_blank">WISE</a> looking for those telltale techno-signatures. So far, no joy for GHAT, but the instruments we have weren't designed to look for such things in other galaxies unless the signal is really strong.<br />
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GHAT <a href="https://arxiv.org/abs/1504.03418" target="_blank">found no definitive evidence of any civilization in about 100,000 galaxies</a> that uses at least 85% of the energy of that galaxy. However, 85% of a galaxy is a tremendous amount of energy, and indicates an extended, focused and sustained period of exponential growth, apparently for its own sake. And, after you are sponging up all the energy in your galaxy and using it for purposes us adorably curious apes can not hope to guess at, what do They do then? The galaxies are very far apart, so the growth craters and they enter a deep recession during which demand for custom built planets is likely to be very low.<br />
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In his forthcoming book, <i><a href="http://www.wowsignalpodcast.com/2016/11/s3-ep-10-human-up.html" target="_blank">Earth in Human Hands</a>, </i>author David Grinspoon points out that unlimited growth will quickly run out of steam - he calls this the Inevitable Expansion Fallacy. Perhaps, be puts to us, really advanced civilizations don't want or need to continue to expand mindlessly, but instead choose to treat their environs - however far flung into the cosmos - more like a garden than a power plant. Perhaps, the lack of evidence from GHAT is good news - very old civilizations, if they exist, are wise and mindful.<br />
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A Stab at a Taxonomy</h3>
Knowing that galaxy scale public works projects are rare is a helpful constraint, but it doesn't mean that there can't be planet-sized structures that advanced ETs might build for specific purposes. Reminding ourselves that epistemic humility is no excuse for epistemic timidity, let's plunge in and make a list of some of the broad categories of purposes of such megastructures. Here I'm relying a bit on the Benfords, who <a href="https://arxiv.org/abs/0810.3966" target="_blank">listed some reasons (not meant to be exhaustive) why ET might build radio beacons</a>. Megastructures, due to their presumably great cost and scale, would likely have different purposes. So, let's make an (probably inaccurate and certainly incomplete) assault on a provisional taxonomy:<br />
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<li>Astronomical megastructures - a massive phased array of optical or radio or some other elements that would permit detection and detail beyond a terrestrial astronomer's fondest dreams. I would expect that these would be built around cooler, dimmer stars - K or M dwarfs. I think this is a pretty reasonable thing to expect an advanced technological civilization to do.</li>
<li>Monument - a civilization has moved on to other things, or is perhaps long gone, and this is a record they have left visible from far away in the galaxy as it eclipses a central star, and is perhaps self maintaining. Think of it as a billion year pyramid. A bright main sequence star would be best, but not the relatively short lived O or B stars.</li>
<li>Energy harvesting and concentration- in addition to <a href="http://www.islandone.org/LEOBiblio/SETI1.HTM" target="_blank">the well-known idea of a Dyson swarm</a>, in which the energy is used locally, the energy might well be directed far out into space by a massive array of mirrors, where it is used for perhaps for propulsion, or even a weapon. A Dyson swarm would exhibit an excess of radiated energy in the mid infrared, but highly efficient mirrors may not radiate much IR excess. We would expect to find such structures preferentially around bright main sequence stars, which are not as numerous as the red dwarfs but bang out much more energy. in the same volume.</li>
<li>Moving the star, or stellar engineering. If you are very patient, you can <a href="https://arxiv.org/abs/1306.1672" target="_blank">use the star's own light to move it somewhere else</a> (this is called a Shkadov thruster). I am not sure why you would want to do that, but perhaps it is the natural extension of the worldship concept. Just move your whole world, including its host star. I don't think that's likely to be the best way to travel, but what do I know? (don't answer that) For such an extended journey, I would thing it would be long-lived main sequence stars that would be favored - class G and cooler. As for stellar engineering, we are really in the dark, but it's probably something quite nefarious.</li>
<li>Purposes humans wouldn't (or can't) think of. I conjecture that this is the largest category, but I don't know what the observables are.</li>
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Nothing Lasts Forever, Of That I'm Sure</h3>
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We should note that any of these structures may be abandoned in any stage of their construction, and even if self-repairing, will eventually become derelict, or will be salvaged for other purposes, so what we would observe could well be the ruins of such a structure. Bits of it might collide and create clouds of smaller bits. Depending on how long you believe such civilizations can survive (remember <a href="https://disownedsky.blogspot.com/2013/02/the-jaws-of-darkness.html" target="_blank">it's all about L)</a>, this could easily be the most prevalent case. </div>
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What Would we Observe?</h3>
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I expect that scenario 1 - a giant astronomical instrument - is the most common type of megastructure, but it may take quite a bit of luck to see it from a distance. The mirror should have a very narrow beamwidth, and unless it's staring right at us (wouldn't that be cool?) we might not see anything. Even if we are luck enough to see some of the mirror transit, we might not see big dips in the host star's brightness as the elements might be fairly diffuse. So, we might have looked right at any number of these and had no idea.</div>
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The megamonuments in scenario 2 should naturally be more conspicuous, but also require more maintenance. They would be designed in multiple orbit planes at different distances from the the host star so that transits were more likely. If you were positioned fortuitously, you might see more than one group transit. </div>
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For the Dyson Swarm, we already know what we think we should see - a big infrared excess. You'd see a peak in the visible spectrum that would be the host star's light, then another peak in the mid infrared.</div>
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For the concentrator, what we might see would be very different. Assuming the concentrator was pointing nowhere near us, we might see a large transit effect. since the mirror would be blocking a significant fraction of the host star's light.<br />
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If the concentrator was pointing in a direction near us, then the star might appear to be much brighter than it's spectral type tells us it should be, and perhaps this will be reflected in the parallax data from the Tycho catalog or in upcoming Gaia data releases. Occasional adjustments or glitches in the pointing of the concentrator elements could result in dips in brightness.<br />
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For Scenario 4, we might see large dips in brightness as the concentrating mirrors transit occasionally. If the purpose is to move the star, there might have already been some progress, so we might see an unusually high Doppler shift, or proper motion, or both. For stellar engineering, I expect we'd see some very odd stuff in the spectral data.<br />
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For Scenario 5, we ape descendants are out of luck for now. We're scratching our fur and looking out into the blackness of the void hoping, that a little seed of concept will go viral in our brains. Probably not any time soon.<br />
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Has This Got Anything to do with Boyajian's Star?</h3>
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Maybe. We don't know that what causes the unusual light curve in KIC 8462852 is an alien megastructure. From the evidence we have so far, I would say scenarios 2 and 3 are the best fits, but scenario 3 has some problems, namely the lack of any observed infrared excess and the fact that the star does not appear to be farther away than its spectral type would indicate, based upon the first Gaia data release. Also, the spectrum looks normal and the motion of the star with respect to Earth is unremarkable, so 4 looks a little shaky, unless they're almost done with moving it and are coming into their new orbital slot.<br />
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So, is Tabby's Star a kind of monument? Or maybe it's just ostentatious signaling, like spending way too much money on your daughter's wedding or buying an ugly McMansion on a tiny lot?<br />
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We may know more soon, but probably what we will learn is how wrong we were....</div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-6289629713733168822016-09-06T16:31:00.000-04:002017-05-22T11:34:38.455-04:00Almost certainly wrong: an alien megastructure speculation about KIC 8462852<div dir="ltr" style="text-align: left;" trbidi="on">
<b>Update: 20 September 2016 - </b><i>with the Gaia DR1, we didn't really know which way <a href="https://arxiv.org/abs/1609.04172" target="_blank">the 300 micro arcsecond systematics</a> would push, us, but now <a href="http://arxiv.org/abs/1609.05390" target="_blank">there is some evidence that the parallax measurements are systematically underestimated</a>. Another nail in the coffin.</i><br />
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<b>Update: 14 September 2016</b> - <i>it would seem that <a href="https://www.reddit.com/r/KIC8462852/comments/52pxi0/gaia_parallax_for_kic8462852_is_2554887_mas/?ref=share&ref_source=link" target="_blank">today's Gaia data release</a> invalidates this, as the the star is no further from us than what Boyajian, et. al., estimated from its brightness, and possibly a fair bit closer. So what we are seeing is a real dimming.</i><br />
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OK, what follows is highly speculative, but as far as I can tell, is at least internally consistent and doesn't require any exotic new physics. I've got some facts in here, but if all you care about is <a href="http://www.songlyrics.com/talking-heads/crosseyed-and-painless-lyrics/" target="_blank">the facts</a>, this isn't for you.<br />
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As <a href="https://disownedsky.blogspot.com/2016/08/aliens-perhaps-but-not-aliens-of-gaps.html" target="_blank">I pointed out recently</a>, to find ET technological civilizations, we're going to have to be wrong a lot - unless they are trying to make it easy for us, which they very well may not be. So, I am a long term optimist but short term pessimist. Unfortunately, being persistently wrong is very painful for some people, many of which might be the most qualified to try and set out the theoretical parameters for ET technology.<br />
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So, let me have a crack at it for <a href="https://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">the case of the star KIC 8462852</a>, commonly referred to on this blog as "Tabby's Star," and I could well be proven wrong in a few days with the first Gaia data release. I will stick to known physics exploited with unknown technology, and perhaps it may take a bit longer to prove me wrong.<br />
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The conjectured megastructure is actually a swarm (conceivably millions) of light sails flying close to the star, using light pressure in clever ways to maintain their positions (I won't detail this yet, because my model of "near field" stellar sailing isn't very good). The megastructure is a shell of reflectors, perhaps within one or two stellar radii (a few million kilometers) of the star's atmosphere. These sails are steered in a coordinated way such that they concentrate the star's light in a particular direction by a high magnification, for the purpose of accelerating (or possibly deaccelerating) a <a href="http://www.lunarsail.com/LightSail/rit-1.pdf" target="_blank">very large light sail</a> and its payload up to interstellar speeds - perhaps a few percent of the speed of light. It would concentrate the star's light by several orders of magnitude.<br />
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Think about it - this star puts out about 10^27 Watts of power, most of it in visible light. If we could<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-z_GlX1nRzWk/V9A8UsBK1CI/AAAAAAAAfdQ/akFR60r116IPOJVlWSSpGDEDF2RX-FIBwCLcB/s1600/Forward_illus.png" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="228" src="https://4.bp.blogspot.com/-z_GlX1nRzWk/V9A8UsBK1CI/AAAAAAAAfdQ/akFR60r116IPOJVlWSSpGDEDF2RX-FIBwCLcB/s400/Forward_illus.png" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Illustration from Robert Forward's 1984 Paper on Laser Sails</td></tr>
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concentrate just one billionth of that power onto a reflective sail, that's 10^18 Watts, or a thrust of almost 10 billion Newtons - a ridiculous amount of thrust by terrestrial standards (probably more than you could use). In 1984, <a href="http://www.lunarsail.com/LightSail/rit-1.pdf" target="_blank">Robert Forward published a conceptual design for such a sail</a> powered by an array of lasers.<br />
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If you build a really huge light sail out of aerospace grade unobtanium - say 1 million square kilometers (a bit <a href="http://land%20area%20of%20texas%20in%20square%20kilometers/" target="_blank">bigger than Texas</a>), it would receive much, much less than a billionth of the star's light at a distance of only a billion kilometers - not far away - so you'd want to concentrate it by a lot, and you'd want to control the amount of concentration - I'm guessing you'd want it to get as high as a million (6 orders of magnitude), but that of course is just a guess. Most of the acceleration would be in close to the star, since just 1 or 2 light years away the thrust would drop off to very low. This predicts that the concentrated beam of light would only be on for the order or decades, or centuries at most, but it would eventually get turned off or steered to another probe.<br />
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This predicts that we are on the edge of this beam (the sail is not being pushed straight at us), or are perhaps looking at a sidelobe of the beam formed from secondary reflections, just as a transmitting radio dish has sidelobes. So, the sharp dips in the star's brightness are glitches, or adjustments in the steering of the beam, and the slow dimming observed is the beam slowly steering off from our direction in a controlled manner.<br />
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This predicts six observable things and a possible seventh:<br />
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<ol style="text-align: left;">
<li>The slow dimming will continue, and then stop when we are out of the beam altogether.</li>
<li>The big dips will continue, but will not exhibit periodicity.</li>
<li>The star is actually quite a bit further away than its brightness would indicate, but its <a href="http://astronomy.swin.edu.au/cosmos/P/Proper+motion" target="_blank">proper motion</a> indicates it can't be extremely further than the current estimate of roughly 1500 light years.</li>
<li>We wouldn't see much IR excess, since the backs of the mirrors are away from us, but we might see a little.</li>
<li>At some point, the probe would be too far away from the star to achieve much acceleration, so the beam might be "turned off" at that point and so there could be a sudden and permanent dimming. Alternatively, a deceleration phase could start, and the sail might become a detectable optical source.</li>
<li>There should be some plausible destination for the interstellar probe, with a line of sight within a degree or so of our line of sight to Tabby's Star (if we want a concentration of 6 orders of magnitude). It should be quite a bit closer to Tabby's Star than we are. The star <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%406816025&Name=TYC%203162-879-1&submit=submit" target="_blank">TYC 3162-879-1</a> might be a candidate. We don't know its distance directly, but it has a bit higher proper motion than Tabby's Star, so might be closer to us, and its line of sight from Earth is only 3 arc minutes (0.05 degrees) from our line of sight to Tabby's Star. There are quite a few other stars that might qualify.</li>
<li>At the destination, there might be another mirror for deacceleration purposes, which would not be "turned on" right now, but would exhibit a significant IR excess when it is.</li>
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-ONxuXQvyLjw/V88cvL4CExI/AAAAAAAAfdA/MDWIUpxcND4wW7dd_inPatZmwlLecDrbwCLcB/s1600/close_star.bmp" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="468" src="https://2.bp.blogspot.com/-ONxuXQvyLjw/V88cvL4CExI/AAAAAAAAfdA/MDWIUpxcND4wW7dd_inPatZmwlLecDrbwCLcB/s640/close_star.bmp" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">One candidate star only 3 arc-minutes from Tabby's Star in our sky (TYC 3162-879-1)</td></tr>
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So, as I freely admit, probably wrong, but is it at least wrong? What do you think?</div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-90453523101594836982016-08-28T21:54:00.000-04:002016-09-09T15:13:15.019-04:00The Possible SETI Target HD 164595 - more messing around with Aladin<div dir="ltr" style="text-align: left;" trbidi="on">
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<i><b>Last Update: 9 September 2016</b></i></div>
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There been a lot of kerfuffle lately about <a href="http://www.centauri-dreams.org/?p=36248" target="_blank">a possible SETI detection</a> more than a year ago at the <a href="http://www.sao.ru/ratan/" target="_blank">RATAN-600 radio telescop</a>e in Russia. Some would say far too much kerfuffle, since it was only seen once and may well admit to alternative explanations. SETI scientists like <a href="https://setiathome.berkeley.edu/forum_thread.php?id=80193#1813506" target="_blank">Eric Korpela are unimpressed</a>.<br />
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Some basic facts about the star:</h3>
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Effective temperature is 5790 deg Kelvin per P<a href="https://arxiv.org/abs/1312.7571" target="_blank">orto del Mello, et. al.(2013)</a><br />
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<a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+164595&NbIdent=1" target="_blank">The SIMBAD Page</a>. The parallax (from Hipparcos) of 35.26 milliarcseconds corresponds to <a href="http://www.wolframalpha.com/input/?i=1%2F(35.26%2F1000)+parsecs+in+light+years" target="_blank">a distance of 92.5 light years</a>. Gaia is unlikely to change this much.<br />
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<a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/328/allwise&AllWISE===J180038.80%2B293420.6" target="_blank">The ALLWISE Page on Vizier</a>. It's <b style="text-align: -webkit-right; white-space: nowrap;">J180038.80+293420.6 </b><span style="text-align: -webkit-right; white-space: nowrap;">in ALLWISE.</span><br />
<span style="text-align: -webkit-right; white-space: nowrap;"><br /></span><span style="text-align: -webkit-right; white-space: nowrap;">no surprise, it's in the 2MASS catalog as </span><b style="text-align: -webkit-right; white-space: nowrap;">18003890+2934188.</b><br />
<span style="text-align: -webkit-right; white-space: nowrap;"><br /></span><span style="text-align: -webkit-right; white-space: nowrap;">Apparently not in the variable star index compiled by AAVSO.</span><br />
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<a href="https://arxiv.org/abs/1506.07144" target="_blank">Here's a reference to the warm Neptune</a> orbiting the star. It orbits the star once every 40 days and is about 16 times the mass of Earth. It was found with a radial velocity search.</div>
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<span style="text-align: -webkit-right; white-space: nowrap;">A companion? Yes!</span></h3>
Unlike Tabby's Star, this star <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%402819247&submit=display&bibdisplay=refsum&bibyear1=1850&bibyear2=2016&Name=HD+164595&Radius=2#lab_bib" target="_blank">has been studied quite a bit</a>, but I'm a little confused by <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+164595&NbIdent=1" target="_blank">this star</a> and its environs. Does <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+164595&NbIdent=1" target="_blank">HD 164595</a> have a red dwarf companion? In Simbad a "sibling" is listed - <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%402819614&Name=HD%20164595B&submit=submit" target="_blank">HD 164595B</a>, and is listed as "rotationally variable star". Is it a companion, or just a nearby star? It has <a href="https://arxiv.org/abs/astro-ph/0610605" target="_blank">a closely similar proper motion</a> (it is slowly moving the same way in the sky at about the same speed). HD 164595 is <span style="background-color: white; color: #010101;"><tt><b style="font-family: Lucida, Tahoma, serif, arial; font-size: 16px;">88194 </b><span style="font-family: "times" , "times new roman" , serif;">in <a href="https://heasarc.gsfc.nasa.gov/W3Browse/all/hipparcos.html" target="_blank">the Hipparcos</a> catalog, and is <i>not</i> listed by <a href="https://arxiv.org/pdf/astro-ph/0610605v2.pdf" target="_blank">Lepine and Bongiorno</a> as having a wide companion. <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-S?WDS%20J18006%2b2934A" target="_blank">It is however, listed in the Washington Double Star Catalog, maintained by the USNO</a>. For now, I think it's probable it does have the M-dwarf companion. Marshall Eubanks has pointed out that this paper by <a href="http://iopscience.iop.org/article/10.1086/381147/pdf" target="_blank">Gould and Chaname says that they are a binary</a>.</span></tt></span><br />
<span style="background-color: white; color: #010101;"><tt><span style="font-family: "times" , "times new roman" , serif;"><br /></span></tt></span>
<span style="background-color: white; color: #010101;"><tt><span style="font-family: "times" , "times new roman" , serif;">Apparently, HD 164595B is not in the Hipparcos catalog (perhaps a bit too dim for that), but should be in the upcoming Gaia data release. It is, however in the 2MASS catalog as </span></tt></span><b style="background-color: white; color: #010101; font-family: Lucida, Tahoma, serif, arial; font-size: 16px;"><tt>J18004543+2933566.</tt></b><br />
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Here is the color 2MASS image, with the two stars side by side. You can see they are about 1.5 minutes of arc apart, which if they are at the same distance, implies a separation of <a href="http://www.wolframalpha.com/input/?i=(1.5%2F60*pi%2F180*92.5)+light+years+in+astronomical+units" target="_blank">about 2550 astronomical units</a>, which is a wide companion. Note the little "objects" just to the south and north of HD 164595 - they're not in any catalog I can find, including 2MASS. I suspect they're not real, but an artifact of how the color image is put together. They don't show up in other images.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-_OG5A8V9__8/V8bmmId_abI/AAAAAAAAfWY/0JCBZGynn4oWsLDEMuYL1i33MpfjF4EEQCLcB/s1600/A_B_labelled_distance.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="238" src="https://1.bp.blogspot.com/-_OG5A8V9__8/V8bmmId_abI/AAAAAAAAfWY/0JCBZGynn4oWsLDEMuYL1i33MpfjF4EEQCLcB/s640/A_B_labelled_distance.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">HD 164595 A and B</td></tr>
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Here's the POSSII image in near infrared. Those stars that appear to be close to HD 164595 are probably much further away.<br />
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<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-KgulkSD4Www/V8OTp5C7MPI/AAAAAAAAfUo/_7AN8aZiQGADAZa0WKP7yjlJTslxc3dSQCLcB/s1600/HD164595.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="640" src="https://4.bp.blogspot.com/-KgulkSD4Www/V8OTp5C7MPI/AAAAAAAAfUo/_7AN8aZiQGADAZa0WKP7yjlJTslxc3dSQCLcB/s640/HD164595.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">POSSII image of HD 164595 in near infrared</td></tr>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-19361972216298337062016-08-20T01:43:00.003-04:002016-09-06T14:47:24.021-04:00The Gaia data release and Tabby's Star - the ELI5<div dir="ltr" style="text-align: left;" trbidi="on">
<i><b>Updated 6 September 2016</b></i>: the bookshelf analogy was a bit muddled - I think I've fixed it.<br />
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On the 14th of September 2016 we are expecting the <a href="http://www.cosmos.esa.int/web/gaia/release" target="_blank">first data release from Gaia</a>, and it could well <br />
<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-dUYErEzGGeQ/V7d5LddcG_I/AAAAAAAAe_I/3_3BIbakxycOp4iNTQE06744Qjf0aKchwCLcB/s1600/gaya_exploded2.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="320" src="https://4.bp.blogspot.com/-dUYErEzGGeQ/V7d5LddcG_I/AAAAAAAAe_I/3_3BIbakxycOp4iNTQE06744Qjf0aKchwCLcB/s320/gaya_exploded2.jpg" width="176" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Exploded view of the Gaia Probe</td></tr>
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turn out to reinforce, constrain, or rule out some favorite conjectures about the weird behavior of a star romantically named KIC 8462852, aka Tabby's Star - behavior that was discovered by exploring the data from the Kepler Space Telescope.<br />
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Now, this is going to get pretty elementary, so if you feel you're already up to speed on the topics in the last paragraph, you may want to skip this.<br />
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Why this star is weird is covered in <a href="https://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">this earlier entry</a>. The TL;DR on that is that it was showing bizarre variations in brightness completely inconsistent with the kind of star it is. We think that we know how the brightness varies, but can't be exactly sure how bright the star is in absolute sense - how many<br />
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The NASA Kepler probe that performed these observations is tightly optimized to do just that - measure variations in brightness of stars. However, this means that it's not particularly well suited to making super precise measurements of star positions. Fortunately, the European Space Agency has <a href="http://www.cosmos.esa.int/web/gaia/science-performance" target="_blank">a sophisticated satellite in space right now</a> that is exactly that - it can measure the distance to over a billion stars using something called the parallax method that I will discuss in a moment. It can also measure the color of stars and how fast they are moving away from or towards us.<br />
<h3 style="text-align: left;">
The Parallax Method</h3>
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The nice thing about parallax is that it is really simple, and you don't need to make any assumptions about a star to measure its parallax. Essentially, we watch a star for a year or longer, and make note of the very tiny variations in its apparent position as the Earth moves around the sun. Simple yes, but since the diameter of the Earth's orbit around the sun is only roughly 0.00004 light years, and the nearest star is just over 4 light years away, it takes a very clean, precise measurement to get this right.<br />
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If you want an obvious example of how this works, stand near a bookshelf loaded with books and hold your index finger straight upright in close to your face. Now, close your right eye - the finger will block your view of a particular book on the shelf. Next, open your right eye and close your left eye. The finger now blocks a different book on the shelf. Finally, move your finger about twice as far from the shelf and try this again. You will see that the two different books blocked by your finger are now closer together. This is how parallax varies with distance - your two eyes are the same distance apart, but the distance to your finger is the interesting variable. An aside note is the amazing job your brain does integrating information from two eyes at the same time - play around with it.</div>
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Let's take a simple look at the math. It turns out that the amount the position in the sky varies over a year - the parallax - is <a href="https://www.mathsisfun.com/algebra/directly-inversely-proportional.html" target="_blank">inversely proportional</a> to the distance - if star A is twice as far away as star B, the parallax of A is half that of B, since the EArth's orbit is <a href="http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Beth_Caissie/eccentricity.htm" target="_blank">reasonably circular</a>. So, using <a href="https://www.wolframalpha.com/" target="_blank">Wolfram Alpha</a>, <a href="https://www.wolframalpha.com/input/?i=(300+million+kilometers)%2F(4*9.467+trillion+kilometers)*180%2Fpi" target="_blank">we'll figure out about what it is for a star 4 light years away</a>, given that a light year is <a href="https://www.wolframalpha.com/input/?i=1+year*(86400+secs%2Fday*365.25+day%2Fyear*300000+km%2Fsec)" target="_blank">about 9.5 trillions kilometers</a>.</div>
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<a href="https://4.bp.blogspot.com/-sflckqCIKEA/V7fkxq4NE5I/AAAAAAAAe_c/Ig3RWoLefaUxIp-4u_dwYoj2Fr9iCmExQCLcB/s1600/Wolfram_parallax_calc.tiff" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="358" src="https://4.bp.blogspot.com/-sflckqCIKEA/V7fkxq4NE5I/AAAAAAAAe_c/Ig3RWoLefaUxIp-4u_dwYoj2Fr9iCmExQCLcB/s640/Wolfram_parallax_calc.tiff" width="640" /></a></div>
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That number is an <i>angle</i> in units of degrees (the 180/pi factor at the end converts it from radians). That is a little sliver of a degree, or slightly more than one <i>arc second</i>, or 1/3600th of a degree. Maybe you can imagine just how hard it is to tell if a star is moving against the background of more distant stars and galaxies by that very slight angle. </div>
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When I was a college student, all the parallax measurements were done with ground based telescopes, and only a handful of stars had accurately measured distance. The problem is that the Earth's atmosphere smears out the light from a star enough that if it is not one of the closest stars, it's parallax becomes impossible to determine.</div>
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Then, in the late 1980s, came <a href="http://www.cosmos.esa.int/web/hipparcos" target="_blank">the Hipparcos mission</a>. Because Hipparcos used a space based telescope, it was able to measure the distances to many more stars using the parallax method - more than 100,000. This was a remarkable achievement and allowed us to recalibrate the distance scales of the entire universe.</div>
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Now, more than 20 years later, we have European Space Agency's Gaia probe. Bringing much more advanced technology to the job of measuring distances, Gaia promises to provide accurate distance measurements for more than 1 billion stars. Even Tabby's star, which is probably hundreds of times further away than the nearest stars, should have its parallax accurately determined for the first time. It was, unfortunately, just a bit too dim and distant for Hipparcos.<br />
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Parallax measurements only depend on the distance to the star. It doesn't matter what type of star it is, or anything else. So, when we get the parallax measurement to Tabby's Star, we'll be able to compare<br />
that to the distance measurement made by measuring its brightness, based upon how bright we think it <i>should</i> be based upon what kind of star it appears to be from its color and so forth. For Tabby's Star, Gaia should be able to measure the parallax down to about 25 millionths of an arcsecond, which is really good, and should give us an accurate parallax.<br />
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Why is this interesting? It is because a couple of different scientific investigations have reported results that show the star unexpectedly dimming on different time scales - <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-6-not-glimmer-of-idea.html" target="_blank">a century</a>, and a few hundred days. <a href="http://arxiv.org/abs/1608.01316" target="_blank">Montet and Simon's paper</a> provides a fine description of this if you want the details.<a href="http://www.wowsignalpodcast.com/2016/08/3-episode-8-ben-montet-makes-star.html" target="_blank"> I interviewed Ben Montet on the Wow! Signal</a>, and got him to explain even further. Think about it - if this is true, it begs the questions of how bright the star was to begin with before it started dimming. Is it possibly considerably closer (weird, but supportive of the dimming hypothesis), or farther away (even weirder), than the current estimate says?<br />
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we'll know on September 14th. Whatever the result, it will be of great interest. However, <a href="https://disownedsky.blogspot.com/2016/08/aliens-perhaps-but-not-aliens-of-gaps.html" target="_blank">don't get your alien magastructures</a> out just yet - we also don't understand how ET technology could have caused the date we observe. We simply haven't been creative enough, and that would also apply to natural explanations as well.</div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-74572271244306727702016-08-06T13:28:00.001-04:002017-07-21T15:37:48.457-04:00Aliens, Perhaps, but Not the Aliens of the Gaps<div dir="ltr" style="text-align: left;" trbidi="on">
<b><i>Update (8 August 2016):</i></b> <a href="http://www.wowsignalpodcast.com/2016/08/3-episode-8-ben-montet-makes-star.html" target="_blank">Audio Interview with Ben Montet</a>.<br />
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With the publication of <a href="http://arxiv.org/abs/1608.01316" target="_blank">Montet and Simon's arresting new preprint</a> showing even more anomalous dimming behavior by <a href="https://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">Tabby's Star</a>, a lot of reasonable people are asking whether it's time to declare this stellar weirdness the work of an ET civilization, or whether it may be soon. While I am emotionally inclined to go this way, and intuitively sense that this may be the ultimate conclusion reached, I am not a believer. There is a fundamental error we still must avoid.<br />
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<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="clear: right; float: right; margin-bottom: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-CqtY6JZAues/V6YPqRxo2aI/AAAAAAAAeu0/FjPyLYvL-_EBbMy-cneV13FWm3w9ZUmYACLcB/s1600/Montet_light_curve.png" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="199" src="https://4.bp.blogspot.com/-CqtY6JZAues/V6YPqRxo2aI/AAAAAAAAeu0/FjPyLYvL-_EBbMy-cneV13FWm3w9ZUmYACLcB/s320/Montet_light_curve.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Light curve for KIC 8462852 from Montet and Simon</td></tr>
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It is not crazy or deluded to think that this could be the work of ET. Not at all. We know that technological civilizations exist in our galaxy, we just don't know how many. It is easy to get into pointless arguments about whether there is just one, or the universe is swarming with creatures in some ways analogous to dexterous, talking monkeys like ourselves. These arguments are usually based upon probability guesses with very weak, or even non existent empirical support.<br />
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The truth is that nobody really knows how common ET civilizations are, or how long they flourish, and the so far null result of our (so far) very poorly funded SETI enterprise isn't much help in resolving it one way or the other, as has been argued by such persons as Jill Tarter for many years now.<br />
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So, saying that it <i>could</i> be ET is not the big mistake. The real mistake is closely analogous to an old argument for the existence of God - now largely abandoned by educated theists - called <a href="https://en.wikipedia.org/wiki/God_of_the_gaps" target="_blank">The God of the Gaps argument</a>. In this argument, what we don't know about our origins or how the universe works is attributable to divine intervention - miraculous actions He must take to bring about that which nature can not - as if the nature of His design is somehow deficient. As science closes down the gaps, this <a href="http://amzn.to/2aQvzbI" target="_blank">god becomes smaller and smaller</a>, and I think you can see why this would be unacceptable to enlightened religious people.<br />
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If we can't argue for the existence of God from the gaps in our understanding of human origins, neither can we argue for aliens based upon the gaps in our understanding of astrophysical phenomena. It's really just re-labelling our ignorance as "aliens." No one should be convinced by this.<br />
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Does this mean there is no scientific path to detecting ET? Of course not, and the decades of slow and patient SETI research point the way. Simple, but testable models of how an ET civilization would choose to advertise its presence are put forth, and there have been quite a few of these. These make testable predictions of what these beacons would be like and how they can be searched for.<br />
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Likewise, much of the focus of research in astrobiology (also with a null result to date) is focused on the question of how will we know extraterrestrial life when we see it. What is clearly different about the observables of a planet (either through a telescope or up close) between one that has life and one that doesn't? This leads to guidance for instrumental, experimental and observational design, going back to Viking lander of the 1970s.<br />
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For phenomena like Tabby's Star, we have to do the same hard work, but it is far more complex than SETI. in SETI, we generally assume that ET wants to reach out to other technological life forms, and will pick a method for communicating with us that is least in principle accessible to us. In other words, in SETI we can assume we know what ET is up to - or were up to, as they may be long gone. For the sort of highly energetic side-effects of ET activity such as a <a href="https://plus.google.com/101996320281322583017/posts/UTEeyMtbF8X" target="_blank">Dyson Swarm</a>, we probably don't know what they are up to, or why. We may not even have a concept to express it. We will have to guess. These guesses would help us determine where to point our telescopes, what parts of the electromagnetic spectrum to search in, and what specific signatures to search for.<br />
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And we will have to be patient, since we will be almost certainly be wrong at first, or perhaps just unlucky in our search. We don't need to nail it exactly, but we will need to develop rough models of ET activity that distinguishes it from unguided nature. These models would more or less fit the data that we think anomalous, would make testable predictions, and would show how to rule out at least known natural phenomena. Such a family of models may be available next year, or it maybe in 100 years, but the more anomalous data we have, the more the models can be constrained. The existence of serendipitously discovered phenomena like Tabby's Star certainly motivates this kind of work, and may even stimulate funding to undertake the search.<br />
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When this work is done, and the data is in, maybe we will know with reasonable confidence that ET Civilizations exist not far from us. It is impossible for us here and now in 2016 to see beyond that point. The thought of our children standing on that threshold and looking out into a living universe with newly enlightened eyes is thrilling to me, and I hope I live to see it.<br />
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-58437915708912848562016-08-04T23:25:00.001-04:002016-08-05T11:30:38.809-04:00Ok, it just got weirder<div dir="ltr" style="text-align: left;" trbidi="on">
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A huge development tonight in Tabby's Star with <a href="http://arxiv.org/abs/1608.01316" target="_blank">publication of Ben Montet's preprint</a>. More soon.<br />
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There will be <a href="https://plus.google.com/events/ca1eb7lnuri3mn7kltb50ah11ik?authkey=CIuHtJjRr-6u1AE" target="_blank">a hangout tonight to talk about it.</a> Message me if you are interested in coming into the hangout, but we are limited to 10 people total.</div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-32127061797977916462016-07-24T23:39:00.001-04:002016-12-20T16:06:43.256-05:00Messing Around in Aladin, part 1 - Tabby's Star and the missing star.<div dir="ltr" style="text-align: left;" trbidi="on">
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<h4 style="text-align: left;">
Last Update: 11 August 2016</h4>
This is another one of those draft entries that I will publish before it is done. I invite comments, questions and criticisms as always.<br />
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Looking into some of the stories I've been covering lately that live right in the imprecise border between astronomy and SETI, I've gotten interested in astronomical catalogs. It turns out that there are a lot of them, compiled over the years by a number of different scientific groups for different purposes. With the advent of astronomy outside the visible spectrum, the number of catalogs has multiplied, and it can be a daunting job to sift through them. I invite you to join me in my confusion and delight as I attempt to navigate my way through this glorious mess our civilization has built.<br />
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<a href="http://aladin.u-strasbg.fr/" target="_blank">Aladin Sky Atlas</a> is astronomy software made available for free from the University of Strasbourg in France. It gives you a graphical interface to a wide range of astronomical catalogs and image libraries. One thing it lets you do is overlay various catalogs across the electromagnetic spectrum around an object, so you can see for yourself what's nearby an object of interest and what its known properties are.<br />
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It turns out astronomers have cataloged far more objects than they have been able to study closely. As a result, there are many things not know about most of the cataloged objects. These are nearly all things that could be known if someone had the time and resources to look into them, but no one has yet.<br />
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KIC 8462852</h3>
So, let's start with Tabby's Star, aka KIC 8462852. Until last year, this was like most other stars we had observed - we knew it existed, and about where it was in the sky, and roughly how bright it was, but had not studied it closely. That has changed now. If you just start up Aladin and query for this object, this is what you see:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-48H1nu7sepI/V5JgsB65cpI/AAAAAAAAedQ/J6A93-TBftwG6v2yh-EDapHA2QylWX-5ACLcB/s1600/Tabby_aladin_start.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://1.bp.blogspot.com/-48H1nu7sepI/V5JgsB65cpI/AAAAAAAAedQ/J6A93-TBftwG6v2yh-EDapHA2QylWX-5ACLcB/s1600/Tabby_aladin_start.jpg" /> </a></td><td style="text-align: center;"></td><td style="text-align: center;"></td><td style="text-align: center;"></td><td style="text-align: center;"><br /></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Tabby's Star shown in Aladin</td><td class="tr-caption" style="text-align: center;"><br /></td></tr>
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The image comes from a set of images called "DSS Colored." You don't have to stick with this one, and can layer images and catalogs on top of it. You'll note in the bottom left corner of the image, a scale showing one minute of arc (1/60th of a degree), and the whole thing is about 15 minutes of arc wide.<br />
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Next, I'm going to zoom in, because I am interested in a more local view, and I want to identify the stars nearby it, so I'll overlay the SIMBAD catalog, which has many of the brighter objects in it. The objects identified by SIMBAD are marked with little red squares:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-q1PE5Ds-DJI/V5Jj70N_HsI/AAAAAAAAedc/3tYV5SpVfLcgPqaIkZprWEeFF0saR_tkwCLcB/s1600/tabbys_zoomed_SIMBAD.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://2.bp.blogspot.com/-q1PE5Ds-DJI/V5Jj70N_HsI/AAAAAAAAedc/3tYV5SpVfLcgPqaIkZprWEeFF0saR_tkwCLcB/s1600/tabbys_zoomed_SIMBAD.jpg" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">A Zoomed in View with the SIMBAD catalog overlayed</td></tr>
</tbody></table>
Tabby's Star is in the middle, we already know it's Tycho 2 catalog number is 3162-665-1. In Aladin, we can click on the neighboring star just to the East, and find out that it's <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=KIC+8462934&NbIdent=1" target="_blank">KIC 8462934</a>, and the star to the Southwest is is <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=TYC+3162-977-1&NbIdent=1" target="_blank">TYC 3162-977-1</a>.<br />
<br />
One of the most useful catalogs is 2MASS, or the 2 micron sky survey, which is a ground based survey in the near infrared (our eyes can't see much longer wavelengths than 0.7 microns). So, let's overlay the 2MASS point source catalog and zoom in a bit more:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://4.bp.blogspot.com/-F_DxOUuOeB8/V5JoF9aMEsI/AAAAAAAAedo/dDmBwDJ1bwYRajlp5M3ep13-fw6iSST9wCLcB/s1600/Tabby_zoomed_2MASS.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://4.bp.blogspot.com/-F_DxOUuOeB8/V5JoF9aMEsI/AAAAAAAAedo/dDmBwDJ1bwYRajlp5M3ep13-fw6iSST9wCLcB/s1600/Tabby_zoomed_2MASS.jpg" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The 2MASS catalog (blue squares) overlayed.</td></tr>
</tbody></table>
<br />
You can see right away that this is a larger catalog than SIMBAD, and has many dimmer objects in it. One of these objects is very close to Tabby's Star in this view, but it could well be much closer or further away. The distance hasn't been reliably measured, and probably the only object in this view that has been closely studied is Tabby's Star itself. There's only just so much telescope time.<br />
<br />
Now let's overlay the mid-infrared catalog formed from the space-based WISE telescope observations shown as green squares. You can't see it very well, but there is a green square on top of Tabby's star, since it is in all three catalogs we have overlayed so far: SIMBAD, 2MASS, and ALLWISE.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-5VHr5_1ibtA/V5JpTSM6qWI/AAAAAAAAed0/70AAN0tiRN8ONrhbazfUcQq_DdQbAczqwCLcB/s1600/Tabbys_WISE_overlay.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://3.bp.blogspot.com/-5VHr5_1ibtA/V5JpTSM6qWI/AAAAAAAAed0/70AAN0tiRN8ONrhbazfUcQq_DdQbAczqwCLcB/s1600/Tabbys_WISE_overlay.jpg" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The ALLWISE catalog added (green squares)</td></tr>
</tbody></table>
Now let's have a closer look at the object "closest" to Tabby's Star in the image, which is known as <a href="http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/246/out&2MASS===20061551%2B4427330" target="_blank">20061551+4427330</a>. Keep in mind that it may not be close at all.<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://3.bp.blogspot.com/-uMvOn_ffAz8/V5JsCTlfG-I/AAAAAAAAeeA/jYbyautHSdYGHyhnpHxpkluq0NFRAsQwgCLcB/s1600/distance_measurement.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://3.bp.blogspot.com/-uMvOn_ffAz8/V5JsCTlfG-I/AAAAAAAAeeA/jYbyautHSdYGHyhnpHxpkluq0NFRAsQwgCLcB/s1600/distance_measurement.jpg" /></a></div>
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Aladin provides a nice little tool for measuring the angular separation, and you can see here the two objects are about 8 seconds of arc apart. That's a tiny angle, and if it and Tabby's Star are somehow at the same distance, then this object is right in the neighborhood - less than a tenth of a light year away. Unfortunately, its distance is not known and its proper motion has probably never been estimated. If it was moving like a bat outta hell away from Tabby's star, that would be really interesting, and would fuel more speculation - mine in particular.<br />
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<h3 style="text-align: left;">
A Disappearing Star?</h3>
<div>
Some clever young Swedish astronomers recently conducted a search for stars that were present in an older catalog (USNO-B), but not in a more modern survey (the Sloan Digital Sky Survey or SDSS). <a href="https://arxiv.org/abs/1606.08992" target="_blank">Their preprint appeared in June 2016</a>, and I <a href="http://www.wowsignalpodcast.com/2016/08/burst-19-lost-stars.html" target="_blank">interviewed Beatriz Villarroel near the end of July</a>. After a lot of hard work on a sample of 10 millions stars from the USNO-B1.0 catalog and comparing it to SDSS, they only found one candidate that passed all the filters they had established.</div>
<br />
http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=II/328/allwise&AllWISE===J145736.52%2B182507.8<br />
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-4289103772003640442016-05-18T14:15:00.000-04:002016-05-18T14:17:09.307-04:00Help catch Tabby's Star in the act - new kickstarter<div dir="ltr" style="text-align: left;" trbidi="on">
Tabetha Boyajian and team have <a href="https://www.kickstarter.com/projects/608159144/the-most-mysterious-star-in-the-galaxy" target="_blank">posted a kickstarter</a> to buy telescope time to monitor <a href="http://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">KIC 8462852</a> photometrically around the world, 24 x7 using a network of telescopes. When a definite dip in brightness is detected, then hopefully the astronomical world will respond by swinging their more sensitive spectrographs and other detectors onto the star, allowing us some hope of really understanding what is going on around this very weird star.<br />
<br />
This would compliment, not replace, the work that <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-5-catching-tabbys-star.html" target="_blank">the AAVSO volunteers are doing</a>. <br />
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I would hope you can see your way clear to donating to both efforts. If enough people show that this matters, it will happen, and maybe, just maybe, a new door will open and we'll see for the first time what is on the other side.</div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-29193421151974051042016-05-06T22:24:00.000-04:002016-05-18T13:11:44.787-04:00Updates to the Century-Long Dimming of Tabby's Star<div dir="ltr" style="text-align: left;" trbidi="on">
In <a href="http://disownedsky.blogspot.com/2016/02/tabbys-star-for-perplexed.html" target="_blank">the main post on Tabby's Star</a>, I brought up the subject of <a href="http://arxiv.org/abs/1601.03256?utm_content=buffer78842&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer" target="_blank">Bradley Schaefer's contention that Tabby's Star is slowly dimming over the course of a century</a> or so, primarily based upon his analysis of <a href="http://dasch.rc.fas.harvard.edu/project.php" target="_blank">the Harvard library of photographic plates</a>. <a href="http://www.wowsignalpodcast.com/2016/02/burst-11-dasch-photometry-with-dr-josh.html" target="_blank">Not everyone agreed with this</a>, but for different reasons. This post is to absorb updates to this story, at least for a while<br />
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Just to be clear, <a href="http://arxiv.org/abs/1509.03622" target="_blank">the initial findings of Boyajian, et. al</a>. concerning the star are based upon the Kepler data, some previous surveys, and follow-up observations, and are not affected by this controversy. It may be an additional piece to the puzzle, but ti may also turn out that Schaefer is wrong. Of course, what we don't know is what happened before the plate library started in 1890, and we have limited information since 1989. If Tabby's Star has in fact been dimming, we don't know how long it has been going on.<br />
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What Schaefer did was to look at both the digitized library and his own estimates of the star's brightness (in a standard band called Johnson B) directly from the plates, using known comparison stars on each plate. He found it necessary to reject a certain subset of plates he found unreliable. He fit both sets of data to a straight line, as well as data for certain "check stars" nearby with similar color. He found that the brightness of the check stars had not changed over the 20th Century, but that Tabby's star had.<br />
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Astronomical brightness is measured on a logarithmic scale, with dimmer stars having a higher magnitude. An easy way to remember it is that a star 100 times dimmer will have a magnitude difference of 5. That is, if one star is magnitude 7, then a magnitude 12 star is 100 times dimmer. So, one or two tenths of a magnitude is a noticeable dimming. Vega, a bright star in the Summer Triangle, is almost zero magnitude, and probably the dimmest star you can see with the naked eye would be Magnitude 6. Astronomers use particular filters to measure brightness, and in the standard "Johnson B" filter, Tabby's Star is is in the neighborhood of 12.2. That makes it pretty dim, but that is because of its distance, almost 1500 light years away. Vega, on the other hand, is quite close as stars go at just about 25 light years away. Tabby's star is actually about 4 times brighter than the Sun.<br />
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When Schaefer studied the B magnitude for Tabby's Star, we concluded that it was dimming relative to his check stars. There is no way that a star like this - a so-called "main sequence" star should exhibit large variations in brightness over such a time period - no one knows of any other exceptions, and some well-validated models tell us that is what we should expect.<br />
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So, is Schaefer right? One of the criticisms of his work is that he used measurements from DASCH that may have issues - the so-called "flagged" measurements. The reasons a measurement might be flagged vary. Schaefer rejected many of these, but not others.<br />
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Let's look at the DASCH light curve for Tabby's Star using the unflagged points only. One you notice right away is that the unflagged points are a small minority of all points. Anyway, here it is:<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-0aHT_X1Tnb8/VsT0FyZGP6I/AAAAAAAAdNU/cv8CiYIJhzo/s1600/lc_K8462852_0_768_131071_1216_398_1%252C0%252C1215%252C398.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="208" src="https://3.bp.blogspot.com/-0aHT_X1Tnb8/VsT0FyZGP6I/AAAAAAAAdNU/cv8CiYIJhzo/s640/lc_K8462852_0_768_131071_1216_398_1%252C0%252C1215%252C398.gif" width="640" /> </a></td><td style="text-align: center;"></td><td style="text-align: center;"></td><td style="text-align: center;"></td><td style="text-align: center;"></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Tabby's Star (KIC 8462852), unflagged measurements only, Kepler Calibration</td><td class="tr-caption" style="text-align: center;"><br /></td></tr>
</tbody></table>
While the curve looks fairly flat, I get that it does show an average decline similar to Schaefer's result. Note that "Menzel gap" starting in the 1950s, during the period when Harvard was not collecting plates because the funding was directed to other projects. The points on the right of the gap are mostly below the average, and the points to the left tend to be above it a bit, but we don't need much dimming to have a real anomaly on our hands. On top of this, B2015 report a recent B magnitude observation (presumably about 2014, but no date is given) of 12.26, which is well below the line.<br />
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Schaefer's check stars don't appear to show this trend when using only unflagged points. In hisl atest preprint in April 2016, he changes the check stars to improve their closeness to Tabby's star both in color, magnitude, and proximity, but the conclusion is the same - Tabby's star varies more than the check stars.<br />
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If you look in Table 2 of Schaefer's paper, you will note that he finds that the B magnitude near the end of the 19th century was about 12.265. That is much brighter than the more recent 1987 magnitude of 12.458 - roughly 20%.<br />
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The <a href="http://aavso.org/" target="_blank">American Association of Variable Star Observers</a>, has been keeping an eye on Tabby's Star since Boyajian, et. al. came out in the fall of 2015. here is what they have seen so far (early May of 2016):<br />
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<a href="https://2.bp.blogspot.com/-a_QLLrev5io/Vy1KhRQB3QI/AAAAAAAAdxw/diLkmOuWkjQo2buCt8lZ02y78qkfi3_lACLcB/s1600/950977091.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="336" src="https://2.bp.blogspot.com/-a_QLLrev5io/Vy1KhRQB3QI/AAAAAAAAdxw/diLkmOuWkjQo2buCt8lZ02y78qkfi3_lACLcB/s640/950977091.png" width="640" /></a></div>
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<div class="separator" style="clear: both; text-align: left;">
The B magnitudes they are seeing are about 12.4 - consistent with Schaefer, but a bit above his trend line. There are subtleties here that are a bit tricky. For example, the bluish-white Tabby's Star is far enough away that there is measurable reddening of its light by the interstellar medium, and I'm not sure this is accounted for in the same way in all systems. </div>
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The AAVSO plots don't show the error bars, and we have a data gap of almost 30 years. Is it possible the star's brightness levelled off in the 1980s and hasn't dimmed all, and maybe even brightened slightly since then? We may never know, but by taking more data, we can monitor longer and longer term behavior.</div>
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As noted in <a href="http://www.wowsignalpodcast.com/" target="_blank">the last Wow! Signal episode</a>, it's now time for the photometry experts to compare notes and hammer out a consensus on this issue. Is there compelling evidence that Tabby's Star is dimming? I think so, but I could wrong - there's a first time for everything.</div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-13242078933192469302016-02-04T09:23:00.000-05:002016-08-05T12:16:49.876-04:00Tabby's Star for the Perplexed<div dir="ltr" style="text-align: left;" trbidi="on">
<div>
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<b><i>Last Update: 5 August 2016</i></b><br />
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<b><i>Update: Montet/Simon Preprint</i></b><br />
Earlier this year, <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-6-not-glimmer-of-idea.html" target="_blank">Brad Schaefer stated</a> that Ben Montet was working on the question of secular fading over the four years of Kepler primary mission data when Tabby's Star was visible, and that he was seeing fading. A <a href="http://arxiv.org/abs/1608.01316" target="_blank">preprint came out last night confirming this</a>, and in fact the fading was quite dramatic at times. There are lots of questions, and I suppose there will be controversy, but it's quite important if it holds up. We'll have more soon.<br />
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Expecting data soon from the the Kickstarter funded observations by the LCOGT. Stand by...<br />
<b><i><br /></i></b><b>Related Wow! Signal Podcast Audio Links:</b><br />
<i><b> <a href="http://www.wowsignalpodcast.com/2016/03/burst-13-tabbys-star-for-perplexed-part.html" target="_blank">Tabby's Star for the Perplexed, Part 1</a></b></i><br />
<i><b> <a href="http://www.wowsignalpodcast.com/2016/03/burst-16-tabbys-star-for-perplexed-part.html" target="_blank">Tabby's Star for Perplexed, Part 2</a></b></i><br />
<b><i> <a href="http://www.wowsignalpodcast.com/2016/01/season-3-episode-3-slow-and-fast.html" target="_blank">The Slow and Fast Dimming of Tabby's Star</a></i></b><br />
<i><b> <a href="http://www.wowsignalpodcast.com/2016/02/burst-11-dasch-photometry-with-dr-josh.html" target="_blank">DASCH Photometry with Josh Grindlay</a></b></i><br />
<b><i> Audio <a href="http://www.wowsignalpodcast.com/2016/04/season-3-episode-3-tabbys-star-for.html" target="_blank">Interview with Tabetha Boyajian</a></i></b><br />
<b><i> <a href="http://www.wowsignalpodcast.com/2016/05/season-3-episode-5-catching-tabbys-star.html" target="_blank">Catching Tabby's Star in the Act - Interview with AAVSO's Stella Kafka </a></i></b><br />
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<br />
When it comes to Tabby's Star (also known as KIC 8462852), we are all perplexed. This post is for those who are disinclined to read technical papers by professional astronomers, but would like to know just what the heck is going on. What is all this stuff about alien megastructures, swarms of giant comets, infrared excess, and old photographic plates? We'll lay all that out here for you in non-technical terms (or we'll explain the terms as we go). Please, if there are any questions, ask in the comments below, and we'll try and figure out an answer, if there is one. The post is richly hyperlinked, so if you want more detail, you can easily find it. I hope I have given credit wherever it is due.<br />
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Let me start by stating up front, that <i>no one</i> knows exactly what is going on with this star. What we'll try to lay out here is why this otherwise ordinary star is strange. If you have questions, or find errors, or know of updates I should include, please leave a comment here.<br />
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<a name='more'></a><br />
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<h3 style="text-align: left;">
The Basic Background Facts</h3>
First, a few basic facts we should all know. Stars vary quite a lot in size, brightness and temperature, but most are small and relatively cool and burn for tens of billions of years. A smaller population of stars are like our own sun, which is called a G class star, and some stars are even bigger and brighter than the sun. Tabby's star (an informal name - it's known in some star catalogs as TYC 3162-665-1 or <a href="http://simbad.u-strasbg.fr/simbad/sim-id?Ident=KIC+8462852&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id" target="_blank">KIC 8462852</a>) is one such, and is called an F class star - a bit bigger, quite a bit hotter, and considerably brighter than our sun. It is just under 1500 light years away (so we are seeing it as it was not quite 1500 years ago), and is in the constellation Cygnus.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-AltmAfdPTRw/VrJTBTR04GI/AAAAAAAAdC8/htfxNnQ4oRY/s1600/Tabbys_star_zoomed%2Bout.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="368" src="https://1.bp.blogspot.com/-AltmAfdPTRw/VrJTBTR04GI/AAAAAAAAdC8/htfxNnQ4oRY/s640/Tabbys_star_zoomed%2Bout.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">KIC 8462852 at the center of the image (visualized with Aladin)</td></tr>
</tbody></table>
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Stars are born in a collapsing cloud of gas and dust, they burn steadily for a while, and then they die. While they are burning steadily, they are called Main Sequence stars, and when they die they change size and color and can vary quite a lot in brightness . Astronomers can study the light from a star and determine the approximate age, just as your vet can tell about how old a cat is by looking at his teeth. Tabby's star is neither very young or very old - it is a main sequence star, and should burn steadily.<br />
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It turns out that Tabby's Star was one of the many stars that the planet-hunting <a href="http://kepler.nasa.gov/" target="_blank">Kepler Space telescope</a> was staring at for about four years (starting in 2009) in an effort to find planets around other stars, or exoplanets. Kepler is able to find exoplanets because for some subset of those stars it is keeping vigil on, its planets will pass across the face of the star from our vantage point, and we will see a very slight dimming of the star when this happens. Although the resulting variation in brightness is subtle, it should repeat in a rhythm that is a fingerprint for such transits, and this fingerprint can be recognized by careful analysis. More <a href="http://kepler.nasa.gov/Mission/discoveries/" target="_blank">exoplanets have been discovered with Kepler</a> than any other telescope - 1039 confirmed exoplanets at this writing. Big exoplanets are easier to detect than small ones, and planets close to their star with shorter period orbits repeat their transits more often, and so are easier for Kepler to spot.<br />
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A problem with the Kepler spacecraft in 2013 meant that it can no longer stare at the same patch of sky that it did at first, so it is no longer keeping watch on Tabby's star. However, the data produced by Kepler continues to be analyzed by astronomers, and notably, by a group of citizen scientists called <a href="http://www.planethunters.org/" target="_blank">Planet Hunters</a>. The Planet Hunters study the subtle variations in stellar light curves by eye, augmenting the sophisticated computer analysis used to detect many of the exoplanet candidates Kepler has found, and flag unusual events in the light curves for follow up by the science team.<br />
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<h3 style="text-align: left;">
What the Planet Hunters Found</h3>
<div>
The first two planets found by Planet Hunters <a href="http://www.astro.yale.edu/mschwamb/Site/Publications_files/2011Fischer-1.pdf" target="_blank">were reported in 2011</a>, and since then they have found quite a few more, but on 17 October 2015, a<a href="http://arxiv.org/abs/1509.03622" target="_blank"> puzzling finding by the Planet Hunters was reported by Boyajian, et. al (we'll just call this paper B2015 from now on)</a>.<br />
<br />
<i><b>Update</b></i>: The 2015 Boyajian, et. al. preprint referred to repeatedly below as
B2015 is now published in the MNRAS. Here is the correct cite: <b><i>(<a href="https://www.blogger.com/goog_1920647810" target="_blank">SIMBAD code: 2016MNRAS.457</a><a href="http://.3988b/">.3988B</a></i></b>)<br />
<blockquote>
T.S. Boyajian, <i>et. al.,</i> Planet Hunters X. KIC 8462852 -where's the flux? - <i>Mon. Not. R. Astron. Soc., 457, 3988-4004 (2016)</i> - <i>14.06.16 11.07.16 April(III) 2016 2016-04</i> </blockquote>
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Here is what the Planet Hunters saw:</div>
<div>
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-2-uWxYZ-13w/VrLGTCxyJ2I/AAAAAAAAdDQ/xbrOg_vLr5I/s1600/Tabbys_dips.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="216" src="https://1.bp.blogspot.com/-2-uWxYZ-13w/VrLGTCxyJ2I/AAAAAAAAdDQ/xbrOg_vLr5I/s640/Tabbys_dips.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">KIC 8462852 Kepler Light Curve reported by Boyajian, et.al: http://arxiv.org/abs/1509.03622</td></tr>
</tbody></table>
<div>
What you are seeing in this chart is a plot of the Kepler measurement of the brightness of Tabby's star (with the normal brightness equal to 1) over the roughly four years the telescope was staring at the star. The downward spikes at around Day 800 (henceforth called the D800 dip) and just after Day 1500 (D1500 dip) are real data, not mistakes, and they are much larger than the normal dips in magnitude observed when a planet transits a large star - typically close to 1%. Two of these dips (numbered 5 and 8) are around 20%, which is only achievable by an object more star sized than planet sized. Dips 9 and 10 are also considerably larger than any planetary transit. There are smaller dips as well, and the B2015 paper identifies the 10 biggest events in Table 1 of that paper. Here's a zoomed-in view of the same graph, in which the ten events are shown:</div>
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<div>
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-aYaZ6sG99mk/VrLNOfeBdVI/AAAAAAAAdDk/rm-YvU7iGBs/s1600/Tabby%2527s_dips_numbered.png" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="186" src="https://2.bp.blogspot.com/-aYaZ6sG99mk/VrLNOfeBdVI/AAAAAAAAdDk/rm-YvU7iGBs/s640/Tabby%2527s_dips_numbered.png" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Normalized Kepler data for KIC 8462852 with dipping events numbered.</td></tr>
</tbody></table>
<div>
Based on its temperature (which can be derived from its color) and type, Tabby's Star is probably more than 2 million kilometers in diameter - more than 50% larger than our sun. By comparison, <a href="http://www.wolframalpha.com/input/?i=diameter+of+Jupiter+in+km" target="_blank">Jupiter is 138,350 km in diameter</a> - so even a large planet would barely cause a dip in luminosity - a few percent at most. Whatever passed in front of Tabby's Star was big - the size of a small star itself, and yet no other close star is in evidence.<br />
<br />
Another important thing to note is the time scale, which you can see for yourself by examining Figure 1 in B2015. The events took place on a time scale of days, and some of them about 10 days. This is a big part of the puzzle.<br />
<br />
I would also note something else I don't know how to interpret, but the team found some evidence that a 48.4 day period is involved. Something orbiting at that period would be about 44 million kilometers from the star, which is quite close. Something that close to such a bright star would be hot, with an equilibrium temperature of 1070 degrees Kelvin, if I did my arithmetic right, and would glow fairly brightly in the infrared at a wavelength of about 3 microns. As we'll see, no evidence of an object emitting infrared light around that wavelength has been found.</div>
<div>
<br /></div>
<h3 style="text-align: left;">
The Planet Hunters Science Team's Follow Up</h3>
<div style="text-align: left;">
There is a lot of information packed into <a href="http://arxiv.org/pdf/1509.03622v2.pdf" target="_blank">the 17 pages of B2015</a>, and I am going to try and unpack it for you, although I am leaving out many details and interesting wrinkles.<br />
<br />
The science team followed up the Planet Hunter's discovery by asking all the obvious questions. Could the data be in error? Are we looking at two or more stars instead of one? Is there something unusual about this star? Does the electromagnetic energy coming from the star give us a clue as to what could cause the dips? It turns out there wasn't a whole lot of astronomical literature on this particular star. There are after all, billions of stars that telescopes can see, and most have not been the subject of close scrutiny. <br />
<br />
The first thing they did was to check with the Kepler team. Had they seen anything like this before? Could it be something wrong with the telescope, or the sophisticated instrument on the telescope's focal plane that measured the brightness of the stars? the Kepler scientists took yet another close look, and shook their heads - the data was real, and wasn't showing up in other star's light curves, as you would expect if it were a problem with the instrument. The Kepler scientists could find nothing wrong with the data - they believe the brightness curve - sharp dips and all - is real.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
The next thing the team did was take a closer look at the data. They tried more sophisticated analysis techniques to try to understand if anything in this complex pattern repeated. If you have multiple things repeating at different intervals, they can "beat" against each other and cause patterns that at first glance have too fast or too slow a rhythm.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
They found that there is a strong component at a 0.88 day period, which the B2015 team argue strongly is caused by the rotation rate of the star itself. Other data in the observational follow-up is consistent with this. Some other interesting bumps were noticed in the frequencies, including a 10-20 day pulsation, but no one knows exactly how to interpret them. They may just be natural variations in the star's brightness.</div>
<div>
<br /></div>
<h4 style="text-align: left;">
Following up with ground based telescopes </h4>
<div>
Boyajian's team followed up the Kepler observations with ground based telescope observations. An examination of observations with the <a href="http://www.ukirt.hawaii.edu/" target="_blank">United Kingdom Infrared Telescope (UKIRT</a>) revealed a tiny speck that may or not be a small companion star. Images from the giant Keck telescope reveal that there is another, fainter star apparently close to Tabby's Star, but it is not clear if it is a distant companion or just another star passing close to the same line of sight. Observations were able to rule a close companion or a bright companion, but it is possible that a red dwarf star circles Tabby's star at a distance.<br />
<br />
The B2015 team were mainly interested in detailed analysis of the star's light, using the science of <a href="http://astronomyonline.org/Science/Spectroscopy.asp" target="_blank">spectroscopy</a>, which is crucial to our entire understanding of the universe. Spectroscopy can not only tell us what sort of elements stars are made of, but since we know what the light spectrum looks like from laboratory work, it can also tell us how fast that material is moving either towards or away from us, since the wavelengths shift up (away) or down (towards) due to the <a href="https://en.wikipedia.org/wiki/Doppler_effect" target="_blank">Doppler effect</a>. Over many generations of studying spectra, astronomers have learned to infer a great deal about a star from its spectrum and measurement of the Doppler effect on it.<br />
<br />
One thing they learned from the spectroscopy was that the star is in fact an unremarkable star, of <a href="https://en.wikipedia.org/wiki/Stellar_classification" target="_blank">a fairly bright, yellow-white class called F</a>, which constitutes about 3% of main sequence stars. The star appears to be rotating fairly fast, with a period of 0.88 days (compare to our Sun's 25 days). They were able to estimate the mass and size of the star, and determine that it is likely to be neither a very young F star, nor very old. If it is in the middle of its life cycle, its brightness should be steady.</div>
<h4 style="text-align: left;">
Radial Velocity Measurements</h4>
<div>
Radial velocity is the movement toward or away from an observer, and can be determined from looking at the spectrum of light coming from a star or galaxy. It is the same technique Edwin Hubble used in the early 20th century to show that the universe is expanding. The radial velocity can do couple of things for us:<br />
<ul style="text-align: left;">
<li>Although no one thinks it's at all likely anyway, it can show that the star is not moving at ridiculously high velocities towards or way from us, which could have weird effects.</li>
<li>If Tabby's star has a large, dark companion that orbits closely, you would expect to see wobbles in the radial velocity.</li>
</ul>
The radial velocity measurements performed on Tabby's Star were not the most accurate possible (you need a bigger telescope and more time), but they were good enough to show that there is no large, dark companion close to Tabby's star, and that its movement through space is nothing extraordinary. We can't however, rule out a big dark companion object further away from the star, but it could not cause both sets of dips, since it would take it too long to orbit the star.</div>
<h4 style="text-align: left;">
Infrared Excess </h4>
<div style="text-align: left;">
If some solid (or liquid) object is absorbing 20% of the energy of the light from Tabby's star in our line of sight, it should heat up, and then basic physics says that energy will be emitted in infrared light, which is just light with a longer wavelength than the human eye can see. So, if we plot the energy we're seeing vs. wavelength of light, then we should see the normal light from Tabby's star, and then a bump out in the infrared, or even in what are called millimeter waves if the object is far from the star and thus not getting as hot. The "bump" is what is called an "infrared excess", and the B2015 team looked for one in the space telescope data available to them, and with a ground based telescope. They did not see any excess.<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://2.bp.blogspot.com/-crfDi_QsKqs/Vr4DPLiZZBI/AAAAAAAAdII/0euVDfbbhgM/s1600/MSP39031dh304eg9af6iid600002f22g9dfe2eig566.gif" style="margin-left: auto; margin-right: auto;"><img border="0" height="300" src="https://2.bp.blogspot.com/-crfDi_QsKqs/Vr4DPLiZZBI/AAAAAAAAdII/0euVDfbbhgM/s400/MSP39031dh304eg9af6iid600002f22g9dfe2eig566.gif" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The heat emission spectrum from an object at 300 degrees Kelvin, from Wolfram Alpha</td></tr>
</tbody></table>
</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
The B2015 team and others looked in the survey data from the WISE infrared space telescope, and later followed up with data from <a href="http://arxiv.org/abs/1511.07908" target="_blank">the Spitzer Space Telescope</a> and with both <a href="http://arxiv.org/abs/1512.00121" target="_blank">an infrared</a> and <a href="http://arxiv.org/abs/1512.03693v1" target="_blank">a millimeter wave telescope</a> on Mauna Kea, and found no clear evidence of anything absorbing the light from Tabby's star and re-emitting it as waste heat. There were some little hints that something might be there <a href="http://arxiv.org/abs/1511.07908" target="_blank">in the Spitzer data</a> at 4.5 microns wavelength, but we shouldn't get our hopes up.Where we would expect to see the infrared spectrum peak depends on your hypothesis about how close to the star the absorber is.</div>
<h4 style="text-align: left;">
B2015 examines some possible explanations </h4>
<div style="text-align: left;">
So, what could explain the dips, and everything we know about them? The lack of an infrared excess ruled out large amounts of solid matter passing in front of a star, as you might have resulting from a major planetary catastrophe, such as two big planets colliding. Also, if this were the case, you would expect the first dip to be much messier, and it is nice and sharp, although asymmetric. The second set of dips is more complex, though. </div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
The B2015 team examined all the more obvious explanations: </div>
<ul style="text-align: left;">
<li>the star itself exhibits variability</li>
<li>big clumps of dust orbiting the star</li>
<li>catastrophic collisions</li>
<li>planets in the process of formation, possibly with very large ring systems</li>
<li>a swarm of large comets</li>
</ul>
</div>
All of these are ruled out by the data, except for the last one. No one knows where such a large swarm of very big comets would come from, although it is at least conceivably consistent with what is known. Comets are can obscure light in a way that would not produce as large an infrared excess - they just boil their material off into space for the most part. B2015 did not consider this explanation a hill to die on, as the MSM seemed to imply in their usually oversimplified reporting, but just the only one they had found so far that they couldn't completely rule out.<br />
<div>
<h3 style="text-align: left;">
Enter the Alien Megastructures - Jason Wright's Comments</h3>
<div style="text-align: left;">
Jason Wright is Penn State astronomer who has been studying ways to seek evidence of technological ET civilizations using astronomical instruments, like infrared telescopes. He heads up the GHAT project, which has done some some interesting work in this area. He also maintains a blog called <a href="http://sites.psu.edu/astrowright/" target="_blank">AstroWright</a>, and at about the same time as B2015 came out, <a href="http://sites.psu.edu/astrowright/2015/10/15/kic-8462852wheres-the-flux/" target="_blank">he posted a blog entry on the same topic</a>. He raises there the possibility that it could <a href="http://arxiv.org/abs/1510.04606" target="_blank">be a very large artificial structure, something that he and the GHAT team had been studying.</a></div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
Wright did not claim that the dips were caused by a transiting megastructure, but just that Tabby's Star was in interesting candidate to study more closely, and a good new <a href="http://www.wowsignalpodcast.com/p/our-threads.html#SETI" target="_blank">SETI</a> target. Note that the lack of infrared excess is a problem for the most common type of concept we have for this, which is a Dyson swarm.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
T<a href="http://www.islandone.org/LEOBiblio/SETI1.HTM" target="_blank">he Dyson swarm</a> (also known as a "Dyson sphere", although this is a misnomer), was first proposed by <a href="http://www.sns.ias.edu/dyson" target="_blank">physicist Freeman Dyson</a> in 1960. It comprises a ring or rings of very large artificial satellites in a circular orbit about a star, absorbing a significant fraction of the star's energy for use by an ever-expanding civilization. While the swarm is under construction (or long after it is no longer in use), it may have large gaps along its orbit path, and its orbit plane may not be oriented so that we would see it transit frequently, if ever. The Dyson swarm would necessarily radiate waste heat in large amounts, at infrared wavelengths around 10 to 20 microns (your eye can't see light with a wavelength of 1 micron or longer), and so far no evidence of this has been seen, as we noted above.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
Of course, Wright's cautious comments were blown out of proportion by the media, and B2015 doesn't even mention the possibility of artificial structures. For a couple of weeks, the headlines proclaimed alien megastructures, until more infrared results came in, in which the authors very cautiously concurred with B2015 that the comet swarm hypothesis was the only one anyone had thought of yet that was consistent with their data. The headlines now read something like, "It's Not Aliens, It's Comets!". Sigh. No responsible person ever said it was either.</div>
<h3 style="text-align: left;">
</h3>
<h3 style="text-align: left;">
SETI Searches in Radio and Optical </h3>
<div style="text-align: left;">
Shortly after the publication of Wright's blog post and B2015, <a href="http://www.seti.org/" target="_blank">the SETI Institute</a> (for whom I have great respect, I want to emphasize) swung into action, using the Allen Telescope Array to look for radio signals from Tabby's Star. Of course, this was a long shot, that 1500 years ago someone orbiting that star should decide to beam a signal our way, in <a href="http://arxiv.org/abs/1511.01606" target="_blank">the frequency bands they were analyzing</a>, over the short window of time over which they looked, but still, they had to give it a shot. After all, "they" would have been looking at the Earth at 1000 B.C., and would have seen no evidence of a civilization that mastered microwaves. <a href="http://www.seti.org/seti-institute/press-release/looking-deliberate-radio-signals-kic-8462852" target="_blank">Nothing was seen</a>, but the array was not at full sensitivity, and they didn't look for a long time. Even with the future, <a href="http://www.wowsignalpodcast.com/2015/03/s2-ep-12-seti-at-ska.html" target="_blank">far more sensitive SKA</a> radio telescope, <a href="http://arxiv.org/abs/1007.0850" target="_blank">we will have to be lucky to eavesdrop on an ET civilization</a>, so the SETI Institute really would only detect a beacon deliberately transmitted in our direction.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
There were also <a href="http://arxiv.org/abs/1602.00987" target="_blank">optical searches looking for laser flashes form Tabby's Star</a>. Again, a long shot, and again, they came up empty.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
The negative SETI searches on Tabby's star to date are a perfect example of a case in which <a href="http://disownedsky.blogspot.com/2013/12/when-is-absence-of-evidence-evidence-of.html" target="_blank">absence of evidence is not evidence of absence</a>. I hope there will be more searches in the future with more powerful telescopes, but we would have to be very lucky to see anything.</div>
<h3 style="text-align: left;">
Bradley Schaefer's Claims that Tabby's Star is Slowly Dimming</h3>
<div>
<a href="http://www.phys.lsu.edu/newwebsite/people/schaefer.html" target="_blank">Astronomer Bradley Schaefer</a> decided to look in the historical archive to find out what it told us about the brightness of Tabby's Star. He is an expert in deriving object brightnesses from old photographic plates, and went to the Harvard library, which holds a large collection of sky survey photographic plates dating back into the late 19th Century.<br />
<br />
A research group called Digital Access to a Sky Century @Harvard (<a href="http://dasch.rc.fas.harvard.edu/project.php" target="_blank">DASCH</a>) has digitized more than 130,000 of these plates and determined billions of object brightnesses and derived millions of light curves, including for Tabby's Star. Anyone can go to <a href="http://dasch.rc.fas.harvard.edu/lightcurve.php" target="_blank">the DASCH website</a> and plot light curves for themselves, although it takes some insight into the process to exclude plates that could skew the data. <a href="http://arxiv.org/abs/1304.7504" target="_blank">Recent improvement to the DASCH processing pipeline</a> have improved brightness measurement errors to about 0.1 <a href="https://en.wikipedia.org/wiki/Magnitude_%28astronomy%29" target="_blank">magnitudes</a> (<a href="http://www.icq.eps.harvard.edu/MagScale.html" target="_blank">a logarithmic measure of observed brightness</a> that <i>increases</i> as a star dims.). Sometimes the error will be less than this, sometimes more. A little <a href="http://www.wolframalpha.com/input/?i=10^%280.1%2F-2.5%29" target="_blank">high school arithmetic</a> will tell you that this error equals about a 9% change in brightness, so we might be lucky and catch Tabby's star acting oddly one or more of the plates. B2015 had examined the DASCH data briefly, but had not seen anything unusual. Schaefer wanted to take a closer look.<br />
<br />
<a href="http://arxiv.org/abs/1601.03256?utm_content=buffer78842&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer" target="_blank">Schaefer's preprint</a> came out in January 2016. This is a paper submitted to the Astrophysical Journal, but not yet accepted for publication. His primary finding was to my knowledge completely unprecedented, and I immediately e-mailed him and requested an interview, which he was kind enough to grant. I had hoped for five or ten minutes, but ended up with over 40 minutes of good material, and it became <a href="http://www.wowsignalpodcast.com/2016/01/season-3-episode-3-slow-and-fast.html" target="_blank">Episode 3 of Season 3 of the Wow! Signal</a>.<br />
<br />
What Schaefer found was that this main sequence star had dimmed by roughly 20% over the century for which Harvard had plates. He found the dimming trend in both in the DASCH data and his own manual measurements directly from the plates (although he has not documented the latter in depth). In both cases, the measurements are made by comparison to known stars on the same plate, so the fact that different telescopes and cameras were used over that century was accounted for. Plates with known problems were excluded from data.<br />
<br />
A main sequence star like Tabby's Star should not dim on these time scales. There is no precedent for it, and well verified models of stellar evolution provide no explanation for it. Schaefer argues that since the star shows anomalous 20% dips on short (days) time scales and over a century, that the same or at least closely related mechanism must account for it. However, this essentially rules out the comet swarm hypothesis because of the the very large number of very large comets required to make this happen.<br />
<br />
However, is this slow dimming real? how likely is it, given the actual data?</div>
<h4 style="text-align: left;">
</h4>
<h4 style="text-align: left;">
The Hippke Paper says there's probably no dimming</h4>
<div>
Shortly after the Schaefer preprint came out, <a href="http://arxiv.org/abs/1601.07314" target="_blank">a rebuttal of sorts was posted on Arxiv by Michael Hippke and Daniel Angerhausen</a>. They argue that Tabby's Star is probably not dimming, becasue they found several other F class main sequence stars in the DASCH database that were also dimming - more than 18 of the 28 stars they were looking at. Shortly thereafter, Schaefer posted <a href="http://www.centauri-dreams.org/?p=34933" target="_blank">a rebuttal to this on the blog Centauri Dreams</a>. This essentially amounts to a claim that the DASCH photometry is not well calibrated.<br />
<br />
Schaefer argued that Hippke was an inexperienced user of the DASCH photometry, and had made mistakes in the selection of stars to be included in his analysis, and that Hippke's stars were not dimming at all.<br />
<br />
I decided to call up the authority on this, Dr. Josh Grindlay, who is the PI of DASCH. In <a href="http://www.wowsignalpodcast.com/2016/02/burst-11-dasch-photometry-with-dr-josh.html" target="_blank">an interview on the Wow! Signal</a>, he told me that he concurred that Hippke's analysis was in error, and that the stars Hippke found were dimming were not dimming. The DASCH photometry has been validated against the so-called <a href="http://adsabs.harvard.edu/abs/1992AJ....104..340L" target="_blank">Landolt Standard Stars</a>, and they show flat light curves for these standards, demonstrating that the DASCH photometry is in fact well calibrated, to the advertised error bars of 0.1 magnitudes.<br />
<br />
However, Grindlay also told me that he was skeptical of Schaefer's results showing that Tabby's star is dimming, since he find that eliminating all but the data points known to be trouble-free results in a flat light curve for Tabby's Star. In his view, Schaefer has more work to do make a convincing case.<br />
<br />
Here is the plot I get from the DASCH website if I turn off all the flagged points, and use the photometric calibrations developed for the Kepler project (the Kepler Input Catalog, hence the acronym KIC). Only 178 points survive all the filters. Here the curve appears to my eye to have a slight downward slope, but the paucity of early points makes it difficult to judge.</div>
<h4 style="text-align: left;">
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://3.bp.blogspot.com/-WAo_xCsPhWc/VrlYAoJgPxI/AAAAAAAAdFs/i6NpPtYtCe8/s1600/lc_K8462852_0_768_131071_898_337_1%252C0%252C897%252C337.gif" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="240" src="https://3.bp.blogspot.com/-WAo_xCsPhWc/VrlYAoJgPxI/AAAAAAAAdFs/i6NpPtYtCe8/s640/lc_K8462852_0_768_131071_898_337_1%252C0%252C897%252C337.gif" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The unflagged points for Tabby's star using the Kepler calibration (not B magnitude)</td></tr>
</tbody></table>
<div class="separator" style="clear: both; text-align: center;">
</div>
</h4>
<h4 style="text-align: left;">
</h4>
<div style="text-align: left;">
From this, I think we have to conclude that the claim of an unexplained long term dimming may be premature, although it remains at least plausible, and we are going to have to wait for further analysis. B2015 presented recent observations and found a blue magnitude ("B" in astronomical parlance) of 12.26, which is substantially dimmer (recall that higher magnitudes are dimmer), than any of the unflagged points early from the 20th Century in the DASCH database. Hippke has revised the initial paper, and significantly adjusted the finding since the initial storm of criticism.<br />
<br />
My own, nonprofessional guess is that Schaefer is right, but he has to persuade his own professional colleagues, not me. If he is right, the mystery of the missing infrared excess deepens. </div>
<h3 style="text-align: left;">
</h3>
<h3 style="text-align: left;">
So, Where are we Now?</h3>
<div style="text-align: left;">
At present, everyone is stumped, and we need more data. The James Webb Space Telescope is still about 3 years away from on-orbit commissioning, and its "first light" image is unlikely to be Tabby's Star. It could be some time before it studies the system in depth. However, skilled amateur astronomers are out in clear nights, keeping a watch on Tabby's star for anomalous dimming events. Since these events last on the order of days, there will be time to swing a big telescope onto the star and attempt to get detailed spectra in the visible and infrared, while smaller telescopes measure the fluctuations in brightness. This could give us a much better idea of what it is that is blocking Tabby's Star. Whether this will solve or deepen the mystery, no one knows.</div>
<br />
<h3 style="text-align: left;">
Some Frequently Asked Questions</h3>
<h4 style="text-align: left;">
Could it be a black hole causing the dimming? </h4>
<div style="text-align: left;">
Dr. Boyajian told me that she frequently gets e-mails proposing that the dimming of KIC 8462852 is due to a black hole.</div>
<div style="text-align: left;">
<br /></div>
<div style="text-align: left;">
No. There are three reasons, all of which are show stoppers to that idea:</div>
<ol style="text-align: left;">
<li>Black holes aren't nearly wide enough. A typical stellar mass black hole is only about 20 km in diameter, which is at least 4 orders of magnitude too small.</li>
<li>Black holes have a lot of mass. The smallest possible black hole is more massive than Tabby's Star, and could be considerably more massive than that. It and Tabby's Star wold be orbiting around the mutual center of mass, and so astronomers should see that in their radial velocity measurements, unless it were orbiting a large distance from the star - in which case, we wouldn't get two events 700 days apart. They simply don't see the radial velocity varying in this way.</li>
<li>A black hole passing in front of the star from our our point of view would make the star <i>brighter</i>, not dimmer, due to a phenomenon known as gravitational lensing, a phenomenon predicted by general relativity, and which astronomers observe all the time at different scales.</li>
</ol>
<h4 style="text-align: left;">
Could it be something in our own solar system blocking the light from Tabby's Star? </h4>
<div style="text-align: left;">
The short answer is no, because these events are on the order of days in duration. Asteroids and planets in our own solar system DO block the light from stars, but these events are much briefer, and they wouldn't look like the D1500 events. Comets close to our sun can partially obscure the light from a star for a while longer, but we would know about them, and Kepler does not look close to the sun.</div>
<h4 style="text-align: left;">
</h4>
<h4 style="text-align: left;">
Does Tabby's Star Have Planets?</h4>
<div style="text-align: left;">
It might very well, since statistically, it seems that nearly all stars have planets. All we know about planets for sure in this case is that Tabby's Star almost certainly doesn't have very large planets close in to the star. The radial velocity data does seem to rule that out, but there could be other planets. However, there don't appear to be any other <i>transiting</i> planets - the sort of planets Kepler is designed to detect. Kepler was only watching the star for four years, so transiting planets with longer than a four year orbit period may be out there.<br />
<h4 style="text-align: left;">
</h4>
<h4 style="text-align: left;">
What about Gravity Darkening?</h4>
<div style="text-align: left;">
In gravity darkening, a fast spinning star is brighter at the poles than the equator. It's not at all clear that without a close, massive companion, gravity darkening would work as an explanation here, even though the star is spinning fairly fast - but not fast enough for gravity darkening to be significant. B2015 did not consider this a candidate explanation, and I think mainly because it is a non-starter.<br />
<h4 style="text-align: left;">
</h4>
<h4 style="text-align: left;">
Since the SETI searches didn't find anything, are aliens ruled out?</h4>
<div style="text-align: left;">
No, not at all. The lack of observed IR excess is far harder to explain if we think the dips are caused by aliens than the (so far) negative SETI results. The searches to date haven't been very long or very sensitive, and would have only seen signals if they were sent toward us deliberately - almost 1500 years ago. If someone with advanced technology was there at that time, then they would not know that there was a technological civilization on Earth capable of receiving signals, even if they wanted to send them. It would be a long shot that they'd send them, and even longer shot that we'd be listening when the signals finally arrived.</div>
</div>
</div>
<h3 style="text-align: left;">
</h3>
<h3 style="text-align: left;">
A compendium of exotic speculations</h3>
<div style="text-align: left;">
So, while we're waiting, let's have some fun. Almost all our speculations are likely to be wrong, but out of these toy models, perhaps some better ideas will emerge. </div>
<h4 style="text-align: left;">
</h4>
<h4 style="text-align: left;">
The highly efficient mirror</h4>
<div style="text-align: left;">
This is actually the best "alien megastructure" idea I have seen, and as far as I know was <a href="http://nextbigfuture.com/2016/02/physics-phd-reader-of-nextbigfuture.html?m=1" target="_blank">devised by Charles Engelke</a>. Some people have proposed that an efficient mirror is positioned close to Tabby's star, and floats on the light pressure - the momentum of the enormous number of photons bouncing off the mirror. The waste heat signal from such a mirror may not be easy to see, as most of the energy is not absorbed, but redirected out into interstellar space, where another large mirror is using it to propel a spacecraft (or some other application we haven't thought of). The waste heat may be hard to spot, not only because there is less of it, but because the temperature of the mirror is very close to that of the star, and so mimics it.<br />
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My question is: would it be possible to see the receiver? It could, after all, absorb or reflect as much 20% of the light from an F class star, so it might be quite bright, depending on how it is oriented with respect to us.</div>
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The swarm under construction </h4>
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If Schaefer is right, then a Dyson Swarm could be under construction, but is still too small to see in IR when it is not transiting. Is that possible, if it is capable of obstructing 20% of the star? As far as I know, no one has considered all the possibilities, but significant infrared excess at a wavelength around 10-20 microns should be observed if 20% of the star's energy is finding its way into waste heat.<br />
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<a href="http://wise2.ipac.caltech.edu/docs/release/allsky/" target="_blank">Caltech's WISE survey</a> included wavelength bands of 12 and 22 microns, so WISE should have seen it. Although the WISE 22 micron wavelength band wasn't as sensitive, my own very crude calculation is that WISE would have no difficulty seeing the IR from such a structure. A quick look at <a href="http://irsa.ipac.caltech.edu/frontpage/" target="_blank">the WISE catalog</a> shows a very weak signal in this band (<a href="http://wise2.ipac.caltech.edu/docs/release/allsky/" target="_blank">W4</a>) for Tabby's star, which may be no better than an upper limit. So, either the structure is very cold, far from the star, or it is incredibly well aligned with our line of sight (so that is is blocking well less than 20% of the star's light overall), or some combination of the two.</div>
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The fragmentary swarm</h4>
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This depends on Schaefer being wrong - that the star has <i>not</i> been dimming on average in the last century, but dimming only takes place during brief events. Here may have once been a Dyson Swarm, but it is no longer in use and has largely fallen apart, been disrupted by collisions, deliberately destroyed,or alternatively, has not been completed yet. They would still absorb light from the star when passing in front of it. but would not produce much IR excess at other times, especially since the surface orientation may be away from us. So, when WISE and Spitzer performed their observations, the signal may have been too weak to pick up. <br />
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Weird physics is being used to modulate the brightness</h4>
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A very advanced technological civilization may be able to control stars use exotic techniques, like a massive pulse of neutrinos.</div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-42715565992695425902016-01-14T16:12:00.000-05:002016-05-18T13:12:31.739-04:00Tabby's Star - Stay Tuned<div dir="ltr" style="text-align: left;" trbidi="on">
I haven't written anything about Tabby's star (KIC 8462852) on here yet, although there was a <a href="http://www.unseenpodcast.com/2015/10/episode-29-im-not-saying-it-was-aliens.html" target="_blank">discussion on the Unseen Podcast</a> a few weeks ago. The latest is <a href="http://arxiv.org/abs/1601.03256?utm_content=buffer78842&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer" target="_blank">a preprint of a paper by Bradley Schaefer</a>, in which he went in detail over the historical data for Tabby's Star and found a surprising result - the magnitude of the star has been steadily dimming over the time of the photographic record he use - the Harvard sky survey photographic plates, which date back to 1890. Depending on what you assume, the dimming is as fast as 0.2 magnitudes per century. Fast - a century is a blink of an eye in the life of a star, so this sort of rapid decline in brightness is not understood.<br />
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Anyway, interviewing Dr. Schaefer very soon, and you will all be able to hear what he says. I'll update this post when it's out. There is a bunch of other stuff to cover, like the initial SETI searches and the lack of IR excess.<br />
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<b>Update</b>: interview concluded, out soon. Subscribe to <a href="http://wowsignal.libsyn.com/rss">http://wowsignal.libsyn.com/rss</a> to get it when it comes out.<br />
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Here's the podcast blog page: <a href="http://www.wowsignalpodcast.com/2016/01/season-3-episode-3-slow-and-fast.html">http://www.wowsignalpodcast.com/2016/01/season-3-episode-3-slow-and-fast.html</a><br />
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-16978082893998018882015-11-25T11:51:00.003-05:002015-11-25T11:59:15.772-05:00Why Interstellar Spaceflight is Hard<div dir="ltr" style="text-align: left;" trbidi="on">
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<span style="font-family: "times" , "times new roman" , serif;"><span style="font-size: small;"><i>This was initially published in audio form as <a href="http://www.wowsignalpodcast.com/2015/10/burst-7-why-interstellar-space-flight.html" target="_blank">Burst 7 of the Wow! Signal</a>. As part of the ongoing effort to tie this blog into that podcast and vice versa, we here present a slightly edited text version of the same.</i></span></span><br />
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">This is a tutorial post, and is largely meant to bring some of our readers up to speed, since we are going to be talking about interstellar space flight more over the next months. If you have ever wondered by we can’t just get on a big rocket and fly to the stars, this is for you. If you already know why we can’t do that, then I think you might want to skip this one. </span></div>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">OK, they’re gone, those nattering nabobs of negativity. Now let’s all just get on that giant rocket and go explore strange new worlds. </span></div>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">Although, maybe we should think it through just a bit before we finish packing our bags. It would be a shame if we left something off of our list, like say, a quadrillion solar masses of fuel. Oops.</span></div>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">Of course, we all </span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: italic; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">want</span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;"> to go and colonize the galaxy (if you have to ask why that is, you may want to skip this as well) , and it seems like it ought not to be more than an engineering problem. OK, let’s assume that you and I are hardy pioneers up for anything (which of course, we are), and look at just the engineering problems. </span></div>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">And, if we’re going to do that, we have to use the laws of physics as they’re presently best understood. Engineers need laws of nature they can rely on, and we let the theoretical physicists worry about what might lie beyond that. The good news is, the physical laws that govern the kind of stuff we know how to build are </span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: italic; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">very</span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;"> well understood. </span></div>
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<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">So, let’s start with what the astronomers know. For well over a hundred years, the astronomers have been carefully surveying the stars around us in the galaxy, and even outside the galaxy. In the 1920s, Edwin Hubble, with lots of help from Milton Humason and building on the work of Henrietta Leavit, figured out about how far away the nearest galaxies were. The results stunned even professional astronomers. The distances were </span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: italic; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">enormous</span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">, and the other galaxies, Andromeda in particular, were </span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: italic; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">huge</span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">. Even fifty years later, Douglas Adams was raving about it. “Space,” he said, “is big. </span><span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is.” He was right. You won’t believe it, and Hubble got a space telescope named after him for figuring it out.</span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">Just four months ago, the New Horizons spacecraft flew past Pluto. With a gravity assist from the <table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-gQTefoBvmsA/VlXoCGRD62I/AAAAAAAAcOo/a-7KpSQAk5k/s1600/NH_Jupiter.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="240" src="http://1.bp.blogspot.com/-gQTefoBvmsA/VlXoCGRD62I/AAAAAAAAcOo/a-7KpSQAk5k/s320/NH_Jupiter.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">New Horizons flew by Jupiter and picked up a gravity assi<span style="color: #252525;">st</span></td></tr>
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giant planet Jupiter, it took New Horizons over 9 years to reach Pluto, and it zipped by it in just a few hours, not bothering to slow down. In rough numbers, Pluto is about 30 astronomical units from Earth, or equivalently, about 30 times further from the Sun than the Earth. That is less than half of a </span><span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: italic; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">thousandth</span><span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;"> of a light year. The nearest star to the Earth is a bit more than 4 light years away, so that the distance to Pluto is about one ten thousandth the distance to the nearest star, and it took us over 9 years with a powerful rocket, a small spacecraft and a gravity assist, to get there, and there was nowhere near enough fuel on board to slow down and orbit Pluto. In the time it takes New Horizons to cover an interstellar distance, it will be a dead, cold space artifact.</span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">Daniel Cartin, whom we’ve had on the Wow! Signal before, <a href="http://arxiv.org/abs/1104.4012" target="_blank">did an analysis of the range a starship would need to really get colonization moving</a>, and it’s around 10 light years for the local solar neighborhood. 10 light years is about one ten thousandth the size of our galaxy, so we are talking about a cosmically short haul. This number might be a bit less for a civilization closer to the center of our galaxy, where the stars are closer together. However, let’s assume you had an amazing rocket that could propel a starship on its journey at 1% of the speed of light. Now remember our ground rules - no unobtainiumm powered warp drives. 1% of the speed of light is very good, actually, as we’ll see. </span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">Now, the best rockets on the drawing board right now might be able to propel a small payload to about 30 kilometers a second, give or take. One percent of the speed of light is </span><span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: italic; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">3,000</span><span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;"> kilometers per second, and lets us get to the nearest star in a few hundred years. We would need 100 times as much velocity boost to get to that speed as our best current rockets. So, just build bigger rockets, then? The problem with this is something called the tyranny of the rocket equation. </span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">The famous rocket equation, which can be derived from Newton’s laws of motion using high school math, says the amount of fuel we need goes up exponentially with the velocity boost we require. This is because a rocket gets heavier as it carries more fuel, and it has to use more fuel to boost that extra fuel, and then more fuel to boost that extra fuel...and the numbers just get completely out of control. A simple calculation shows that we need more than ten to the forty-third power as much fuel as we used to get to 30 kilometers per second. That’s just not going to happen. Sure, we could try to get clever about staging, or ion engines, reducing the mass of our payload, or what have you, but there’s only so much you can do, and we haven’t even talked about the propulsion we need to slow down as we arrive. Old school rockets as we know them just aren’t going to get us there.</span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">We haven’t even talked about energy. As you probably remember from high school, the energy in a moving object is the total work required to get it moving that fast, and goes up as the square of the speed, until you get close to the speed of light, where it goes up faster than that. Now, the New Horizons spacecraft, which is small as spacecraft go, has a mass just under 500 kilograms. That same mass, at 1% of the speed of light, has an energy of more than 2000 Terajoules, and it will still take more than 1000 years (remember, it has to slow down at the end), to cover the required 10 light years. 2000 Terajoules is roughly the electrical generating capacity of a major developed nation for an hour, and New Horizons, as we have pointed out, would be a very tiny starship that wouldn’t survive the journey. Although 1000 years is a cosmic twinkling of an eye, on a human scale, it seems too long. In reality, we are going to need hundreds of thousands or even millions of times more energy than that, and we have to generate it in space. The biggest power system now operating in space is the solar array on the International Space Station, generating up to 90 kiloWatts in orbit around the Earth. We are many orders of magnitude away from producing enough energy for a practical starship.</span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">So, we need to either be willing to take a very, very long time to travel between stars, or come up with something else besides the technology we have now.</span></div>
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<span style="background-color: white; color: #252525; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline;">What that something else is will be the subject of future posts. We haven’t even gone into the problems of very long duration spaceflight, or how to slow down once we arrive, or the hazards of traveling through interstellar space at a significant fraction of the speed of light, how we’re going to phone home when we arrive, or even if there will be a home to phone to after all that time - but we should. We’re going to need engineering we don’t know how to do yet. As it is, we struggle with how we’re going to get humans to our near neighbor Mars - in such a way that they have a fighting chance to survive. </span></div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-1436585534656095222015-11-20T12:20:00.001-05:002015-11-25T21:29:38.635-05:004 Pi SETI - Why Not Build the Argus Radio Telescope Full Scale?<div dir="ltr" style="text-align: left;" trbidi="on">
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<tr><td style="text-align: center;"><a href="http://www.wowsignalpodcast.com/2014/11/season-2-episode-7-actually-wow.html" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;" target="_blank"><img border="0" src="http://1.bp.blogspot.com/-4Sgck9WO6QA/VGrNbQ9_1cI/AAAAAAAAALA/vvVt7ZsKSx0/s1600/Dixon.jpg" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Robert Dixon</td></tr>
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<i>Update: we need to <a href="http://arxiv.org/abs/1511.07746" target="_blank">digest this first</a>. All-sky there could be 2000 FRBs per day.</i><br />
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This post - like nearly all the others - is about the questions I have. I am not a radio astronomer.I want to know how and how much and when about the radio telescope we will discuss below. This was stimulated by my <a href="http://www.wowsignalpodcast.com/2014/11/season-2-episode-7-actually-wow.html" target="_blank">interview with Robert Dixon last year</a>, in which he discussed the <a href="http://ohioargus.org/" target="_blank">virtues of the Argus concept</a>. I lay awake that night thinking about it, and wondering why it hadn't been built yet.<br />
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The Search for Extraterrestrial Intelligence (aka SETI) is just that - a search. Like any search, it becomes much more difficult when more dimensions are added to the search space, and far easier when one or more of those dimensions are removed.<br />
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For example, if you are looking for an obscure little store with the best barbeque ribs in the West, and all you know is that it's in Los Angeles County, then your search space is quite large. However, if you have the additional information that it's on Santa Monica Boulevard, then you you still have some searching to do, but much, much less. You might even find the joint before it closes.<br />
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The problem with the SETI search is that it uses telescopes, and telescopes like the <a href="http://www.seti.org/ata" target="_blank">Allen Telescope Array</a> or the <a href="http://www.planetary.org/explore/projects/seti/seti-at-home.html" target="_blank">Arecibo Observatory</a>, only look at a small part of the sky at any one time. In fact, all the radio observatories in the world put together are only looking at a tiny sliver of the sky. If an ET beacon is transmitted for a short time while you are looking at another part of the sky (which you almost certainly are), you would completely miss it. We can dream about adding more telescopes to the search, but we would need a ridiculous number to cover the whole sky at once - or would we?<br />
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There is an alternative telescope design that uses a combination of a large number of simple, cheap receiving elements and high speed processing to cover the entire sky at
once. At longer wavelengths, these
telescopes already exist: like <a href="http://www.lofar.org/" target="_blank">LOFAR in Europe</a>, <a href="https://www.ovro.caltech.edu/" target="_blank">Owens Valley in the US</a>, the <a href="http://www.tauceti.caltech.edu/leda/index.php/host-facilities" target="_blank">Long Wavelength Array</a> in New Mexico, and soon Phase 1 of the low frequency array as part of the <a href="https://www.skatelescope.org/australia/" target="_blank">Square Kilometer Array in Australia</a>, which should work as a faster, more sensitive LOFAR.<br />
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The <a href="http://www.atnf.csiro.au/projects/askap/index.html" target="_blank">ASKAP in Australia</a>, currently under development, will reach frequencies up 1.8 GHz (well above the 21 cm Hydrogen line, near where the Wow! Signal was observed), but with 30 square degrees of FOV, which is hardly the whole sky.<br />
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A prototype of a full-sky radio telescope that covers more wavelengths of SETI interest, but which is too small to be adequately sensitive, is called <a href="http://ohioargus.org/" target="_blank">Argus, and was built on a rooftop at Ohio State University</a> with a tiny budget. However, <a href="http://www.bigear.org/argus_england.htm" target="_blank">Argus</a> is mainly built out of computers, and it scales up well and benefits directly from Moore's Law. Just a decade or so ago ago, a large Argus array required too much computing power, but now is easily within reach with inexpensive computers. We could build a large one with simple, easily maintained elements and a building full of computer racks for a fraction of what the Square Kilometer Array would cost.<br />
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<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-huWZGMOIY2U/VkoJHzqc9fI/AAAAAAAAcKU/9-j_5rcYddE/s1600/ARGUS.png" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="239" src="http://3.bp.blogspot.com/-huWZGMOIY2U/VkoJHzqc9fI/AAAAAAAAcKU/9-j_5rcYddE/s320/ARGUS.png" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Experimental Argus array at Ohio State</td></tr>
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In addition to the building full of computing racks and routers, you need a fiber optic connection, and a flat open space of land filled with a large number of simple receiving elements. The number of antenna elements you would need at 1500 MHz (the radio astronomy band most commonly searched), would be <a href="http://www.ece.vt.edu/swe/mypubs/04447343_Argus.pdf" target="_blank">about 10000 elements to detect short transients at a strength of 150 Jansky</a>, or roughly <a href="http://www.bigear.org/Wow30th/wow30th.htm#flux" target="_blank">comparable in strength to the Wow! Signal</a> (which was a longer transient). This would not detect most of <a href="https://en.wikipedia.org/wiki/Fast_radio_burst" target="_blank">the Fast Radio Bursts so far observed</a>, so a case might be made for an even larger array, depending on what progress is made understanding the FRBs in the interim. These elements could be produced inexpensively at such quantities - perhaps a few hundred dollars apiece. The exact number needed will depend on how sensitive we want the array to be - if we want it to able to detect events like <a href="http://www.planetary.org/blogs/guest-blogs/2014/0514-the-case-of-the-5-millisecond-cosmic-radio-burst.html" target="_blank">the 5 millisecond Lorimer Burst</a>, we may need quite a bit more than 10,000 elements.<br />
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I am going to roughly cut a number of $5 million for land and buildings, $10 million for the antenna elements, electronics and cabling ($1000 for each element including installation cost) , $10 million for engineering, software and project management, and $10 million for the baseband equipment (computer, networking, etc.). That's $35 million. And, since I am probably wrong by at least a factor of two, let's say $70 million for the entire facility, and we may want another, essentially duplicate telescope in the opposite hemisphere, so just under $150 million for the complete, deluxe, capability covering nearly all of the celestial sphere at any time. Compare this to the <a href="https://www.skatelescope.org/project/" target="_blank">more than $2 billion the Square Kilometer Array is projected to cost at completion</a>. <br />
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These facilities would filter their data down to
actual transients, removing obvious sources of interference such as satellites, and and forward the results to a science center somewhere
that would have their finger on the button to turn more sensitive telescopes across the electromagnetic spectrum onto transient sources, similar to <a href="http://4pisky.org/" target="_blank">Oxford's 4 Pi Sky</a> organization. <br />
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Unlike the SKA, performing sensitive astronomy on relatively small fields of view, the big ARGUS would survey the entire sky over a wide range of frequencies, looking for unexpected transients. Such events are mostly going to be natural, and would be of interest to respectable radio astronomers doing real science, but if ET beacons, as I posit, are transmitted for only a short duration in our direction, we would have a much better chance of finding them.<br />
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The value of doing this depends on your hypothesis on how frequently and for what duration clear ET beacons appear in the sky. If you posit that they happen frequently, then in time you will happen upon one by chance while doing <a href="http://www.wowsignalpodcast.com/2015/03/s2-ep-12-seti-at-ska.html" target="_blank">commensal SETI with the SKA</a> or Arecibo or the <a href="https://science.nrao.edu/futures/ngvla/science-working-groups" target="_blank">next generation Very Large Array</a> (presently in the conceptual design stage), or targeted SETI searches as part of <a href="http://www.wowsignalpodcast.com/2015/09/season-3-episode-1-breakthrough-listen.html" target="_blank">the Breakthrough Initiative</a>. If you posit, as I do, that these events are rare, then the money spent on a bigger, more sensitive ARGUS would be a good investment, and there are <a href="http://www.faculty.ece.vt.edu/swe/argus/um040430.pdf" target="_blank">transient natural phenomena we would catch as well</a>.<br />
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So, the question I have is, why not? Spread over several years and multiple phases, construction would only cost a few million per year and could be architected to exploit improving computer technology. However, it appears that little work has been done on Argus, since the <a href="http://www.faculty.ece.vt.edu/swe/mypubs/04447343_Argus.pdf" target="_blank">2008 paper by Ellingson, Hampson, and Childers</a>.<br />
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Radio telescope arrays are under construction as mentioned above, but focus primarily on long wavelength arrays for measuring heavily redshifted signals from the early universe. The next generation VLA currently in planning is a radio telescope similar in architecture to the Square Kilometer Array - many apertures but <a href="https://science.nrao.edu/futures/ngvla/concepts" target="_blank">fairly narrow fields of view</a>. Although I'm not aware of a cost estimate for the ngVLA, it would have to be comparable to the SKA, possibly even more. For a fraction more, we could colocate a large Argus with it, and spot transients it could potentially target.<br />
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With an affordable full-scale Argus, we would not completely remove two spatial dimentsons from the search - instruments like the SKA are far more sensitive in the narrow beams that they search within than the Argus can be without approaching these instrument in cost. <br />
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I need help at this point. What am I missing? Is the overall science case weaker than I think, with or without SETI as a priority? Or would it cost far more than I estimate? Or is it just not as sexy as an array designed for unprecedented sensitivity? What else? If you're knowledgeable on these matters, I'd love to hear from you.</div>
Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0tag:blogger.com,1999:blog-1473380388569472779.post-5275382520417821422015-11-17T23:34:00.001-05:002015-11-19T15:58:22.516-05:00Questions about Asteroid Mining<div dir="ltr" style="text-align: left;" trbidi="on">
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What follows is based closely upon the <a href="http://www.wowsignalpodcast.com/2015/11/burst-8-questions-about-asteroid-mining.html" target="_blank">Wow! Signal Podcast's Burst 8</a>.<br />
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Lately, it’s been my sense that it’s time to spin up the asteroid mining conversation in earnest. Our most </span><a href="http://www.unseenpodcast.com/2015/11/episode-33-extract-resource.html" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">recent Unseen Podcast episode (#33) </span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">covered asteroid mining, and space policy expert James Muncy joined us for the first part of the show. We received a comment on the blog post for this episode by “Khani”, and here it is verbatim:</span></div>
<b id="docs-internal-guid-4720e85b-18dd-9314-a562-f5c91dbfdd01" style="font-weight: normal;"><br /></b>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-left: 36pt; margin-top: 0pt;">
<span style="background-color: white; color: #333333; font-family: "arial"; font-size: 13.333333333333332px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Question - (case 1) I travel to an asteroid of 100 meters in size. I start extracting materials from the "equatorial" zone. Is the material mine? (case 2) is the asteroid mine? (case 3) I move the asteroid, and now someone else lands on the other side and starts harvesting it. Is that "illegal" ? How much does the asteroid to be moved to be claimable? One meter?</span></div>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Respectable test cases, I think, but we can go further. </span><br />
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;"></span><br />
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">While I don’t think intentionally moving all but the smallest asteroids is likely to be much of an issue, it does raise the question of operations around the so-called </span><a href="http://neo.jpl.nasa.gov/neo/groups.html" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">potentially hazardous asteroids, or PHAs</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">. We talked about these last year with </span><a href="http://www.wowsignalpodcast.com/2014/12/season-2-episode-8-incoming-asteroid.html" style="text-decoration: none;"><span style="background-color: transparent; color: #1155cc; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: underline; vertical-align: baseline; white-space: pre-wrap;">Jose Galache, Season 2, Episode 8</span></a><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">. As of this writing, JPL identifies 1634 PHAs - asteroids that at some time in the future could pass close to the Earth and are at least 150 meters in size. This lower limit is small enough that mining activity at the asteroid could affect its orbit. While this doesn’t directly affect the issue of whether the mined material is the property of the miners, it certainly does raise the question of how we could safeguard against the weaponization of asteroids, or even the unintentional budging of an asteroid into the Earth’s path. I don’t know the answer to this, but I think it’s a fair question, and of those 1634 PHAs, there is a fair chance that one or more is ore rich, and can bring this issue up.</span></div>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Then there is the question of conflict over a single, particularly rich asteroid that may attract more than one mining operation. My understanding of the new US law, is that only the extracted resources are owned by the miner, and there is nothing to prevent another miner from mining the same asteroid. You can see how this could get out of hand, and would seem to point to the need for an unambiguous claim system. The claim would be for the surface and subsurface area that is intended to be mined, not just for what has been mined so far. What might easily emerge from this would be a trading market in asteroid claims. You can see how it can get complicated.</span></div>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">How big could a claim be? Should there be an arbitrary size limit? Or , is there a smarter way to to give everyone a fair shot at mining a larger asteroid? Again, I don’t know the answer, but I hope smart legal minds are thinking about it.</span></div>
<b style="font-weight: normal;"><br /></b>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">So, my most burning question that emerges from this, is: is in-situ prospecting - actually going to the asteroid and confirming that it is rich in a desirable resource - sufficient for staking a claim, that can be subsequently sold? I would think so, but the lawyers have not yet had their say. Again, complicated, but it could encourage the high risk of prospecting if the potential payoff is short term and lucrative. Again, I don’t know the answer, but I think it should be yes. Can you convince me otherwise?</span></div>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">It’s not just me that doesn’t have the answers, but I don’t think anyone does definitively, because there have been no test cases. My fervent hope is that these cases are settled in court, and not by vicious robot battles. It’s very hard for me to see how there could be winners from a violent conflict in space. So, this represents an opportunity to establish an international - or day I say, interplanetary - court to adjudicate conflicting claims on space resources. Such a court would hopefully set carefully reasoned and forward looking precedents with their decisions.</span></div>
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<div dir="ltr" style="line-height: 1.38; margin-bottom: 0pt; margin-top: 0pt;">
<span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">Let’s continue this conversation. If you’re knowledgeable on these matters, please contact me</span><span style="background-color: transparent; color: black; font-family: "times new roman"; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; text-decoration: none; vertical-align: baseline; white-space: pre-wrap;">, and let’s talk. Or, just leave a comment on this blog post.</span></div>
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Paul Carrhttp://www.blogger.com/profile/16996381651333056350noreply@blogger.com0