Wow! Signal Pub 2 - let's talk.

It will be next Friday night, 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.

Last Friday, we did a technical rehearsal, which went well. Feel free to watch it on YouTube if you want. It's almost a Pub 1.5.

More Aladin on a rainy day - Gaia Alert 16bao

Update 17 Jun 2019: Some folks on /r/KIC8462852 think this is probably an eclipsing binary, and they make a decent case, but I still have questions.

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.

The star first came to my attention as the source of Gaia Alert 16bao 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.

Here is the light curve from Gaia alert 16bao:

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 Boyajian's Star. The dips are too deep, aperiodic and irregular for an eclipsing binary.

The Gaia alert gives the J2000 coordinates as RA=297.72688 degrees , and Dec = 23.55513 degrees. We can plug this straight into Aladin Sky Atlas to see what's there.  Right away we can learn several things.

KIC 8462852 Analysis - you can participate

Tabby Boyajian has a new initiative 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 the Wow! Signal.

The new initiative is about making telescope images in various wavelength bands from the Las

One of the Las Cumbres Telescopes

Cumbres Observatory network available in a regular basis for community analysis. These images will be centered around Boyajian's Star.

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.

The best way to get started is to go on over to the subreddit set up for this purpose, and ask your questions. Download and install AstroImageJ, 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.

You will be participating in solving a scientific mystery. We don't know where the very fine dust is coming from that is causing the deep dips in brightness Boyajian's Star, and there is very likely other material involved that we haven't yet got much of a clue about.  The way these kinds of mysteries are typically solved is through lots of persistent and consistent effort by lots of people. Why not you?

A quick note on Useful and Useless Things

I have started a new video playlist about things I find useful. If you are so inclined, I hope you'll give it a watch from time to time. Here's the first one.

More fun with Aladin - Gaia Alert Gaia18adn

You've probably heard of the European Gaia mission. 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.

When Gaia spots a transient, a photometric science alert 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.

The most recent one that caught my eye was Gaia18adn. 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 2059140431331158272, if you're keeping score.

The Elsie Paper

Note: after this was nearly done,  couple of people pointed out to me the simultaneous release of a preprint by Deeg+ that reaches essentially the same conclusion as the Boyajian+ paper, but uses a different method, and covers all 4 2017 dips.

This post is a slightly updated text version of Wow! Signal Burst 25, which was was being released on the 3rd of January 2018, almost simultaneously with a press release announcing a new paper on Tabby’s Star by Boyajian, et. al., titled The First Post-Kepler Brightness Dips of KIC8462852 

In a previous post, 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 Tabby's Star for the Perplexed. We also had a conversation with astrophysicist Eva Bodman on the Unseen Podcast in October 2017 in which we discussed recent developments.

I'm still perplexed - Tabby's Star Update for November 2017

Update: 29 November 2017

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.

The tl;dr

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.

July 2017 Update on Tabby's Star

If you want to know what is going on day to day with Tabby's Star, then the site Where's The Flux is an excellent resource. If you want to catch up on the basic info with sourced facts, you might want to check out the Wiki on /r/kic8462852. 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.

In this post I'll try to create a bit more context without going overboard on the speculation. People love speculating on this star (as do I), 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.

More on the AAVSO trends for Boyajian's Star

My earlier post on the dimming 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.

A conclusive non-conclusion about dimming in the AAVSO data

I'm spending too much time on this, so will have to bring it to a close until the summer's observing is done.

I took one more look at the AAVSO data, this time doing something called binning, similar to what Brad Schaefer did with the DASCH data 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, the model is a simple straight line. 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.

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.

The V Band Fit with 10 day binning

Brute Force and The AAVSO Data on Boyajian's Star

We have more than 500 days span of data from the AAVSO data on Boyajian's star now. I thought it might be worth a closer look to see if any of the secular dimming seen by either Schaefer in the archival plates or Montent and Simon in the Kepler full frame images might still be going on.

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.

A little background information

So, a brief explanation of what the AAVSO does. 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.

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.

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:

1. A higher magnitude means the source is dimmer.  The brightest things in the sky have a negative 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.
2. A small difference in magnitude is a big difference in brightness, because the scale is logarithmic. 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.

The AAVSO Data so Far

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.

The Absolute, Definitive Truth About Alien Megastructures

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.

Update 8 December 2016: 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...

The Usual Disclaimer

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.

But I'm Completely Serious

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. I've written before about why I think SETI is worthwhile.

Almost certainly wrong: an alien megastructure speculation about KIC 8462852

Update: 20 September 2016 - with the Gaia DR1, we didn't really know which way the 300 micro arcsecond systematics would push, us, but now there is some evidence that the parallax measurements are systematically underestimated. Another nail in the coffin.

Update: 14 September 2016 - it would seem that today's Gaia data release 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.

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 the facts, this isn't for you.

As I pointed out recently, 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.

So, let me have a crack at it for the case of the star KIC 8462852, 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.

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 very large light sail 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.

The Possible SETI Target HD 164595 - more messing around with Aladin

Last Update:  9 September 2016

There been a lot of kerfuffle lately about a possible SETI detection more than a year ago at the RATAN-600 radio telescope 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  Eric Korpela are unimpressed.

The Gaia data release and Tabby's Star - the ELI5

Updated 6 September 2016: the bookshelf analogy was a bit muddled - I think I've fixed it.

On the 14th of September 2016 we are expecting the first data release from Gaia, and it could well

Exploded view of the Gaia Probe

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.

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.

Aliens, Perhaps, but Not the Aliens of the Gaps

Update (8 August 2016): Audio Interview with Ben Montet.

With the publication of Montet and Simon's arresting new preprint showing even more anomalous dimming behavior by Tabby's Star,  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.

Light curve for KIC 8462852 from Montet and Simon

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.

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.

Ok, it just got weirder

A huge development tonight in Tabby's Star with publication of Ben Montet's preprint. More soon.

There will be a hangout tonight to talk about it. Message  me if you are interested in coming into the hangout, but we are limited to 10 people total.

Messing Around in Aladin, part 1 - Tabby's Star and the missing star.

Last Update: 11 August 2016

This is another one of those draft entries that I will publish before it is done. I invite comments, questions and criticisms as always.

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.

Aladin Sky Atlas 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.

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.

Help catch Tabby's Star in the act - new kickstarter

Tabetha Boyajian and team have posted a kickstarter to buy telescope time to monitor KIC 8462852 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.

This would compliment, not replace, the work that the AAVSO volunteers are doing.

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.

Updates to the Century-Long Dimming of Tabby's Star

In the main post on Tabby's Star, I brought up the subject of Bradley Schaefer's contention that Tabby's Star is slowly dimming over the course of a century or so, primarily based upon his analysis of the Harvard library of photographic plates. Not everyone agreed with this, but for different reasons. This post is to absorb updates to this story, at least for a while

Just to be clear, the initial findings of Boyajian, et. al. 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.

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.

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.

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.

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.

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:

 

Tabby's Star (KIC 8462852), unflagged measurements only, Kepler Calibration

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.

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.

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%.

The American Association of Variable Star Observers, 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):

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. 

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.

As noted in the last Wow! Signal episode, 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.