If you’re looking for a guide to this series, click here.
I’ve just re-submitted a paper, which I expect to be accepted soon in light of a very favorable and constructive referee’s report, about KIC 8462852. It covers the puzzle as I see it now, the landscape of solutions—from the plausible to the all-but-impossible—and opportunities for future progress. I’m especially excited for the GAIA parallax, which will really help us to narrow things down!
So I’m going to slow-blog the paper over the next week or so, up until the day it actually appears on the arXiv (after it’s accepted).
OK, let’s go!
The Story So Far
Dr. Tabetha Boyajian (now an assistant professor at LSU) first announced KIC 8462852 to the world in a paper that described how it was discovered, how it is an apparently ordinary F star except for its bizarre series of photometric “dips,” and how hard she and her co-authors, including Prof. Saul Rappaport, worked to solve the puzzle. I’ve blogged previously about the whole story, including the subsequent media coverage here, and you should read that to catch up if you’re not familiar with the star. I also gave a talk about it that you can watch here:
Then Bradley Schaefer looked at old DASCH photometry and found that Boyajian’s Star has been fading over the past 100 years, a claim at least as extraordinary as the star’s Kepler light curve. There was a lot of shouting over this claim, and whether it was right, which Kimberly Cartier and I documented in an article for the Atlantic, linked in this blog post.
The big news recently is that Ben Montet & Josh Simon very cleverly recently used the Kepler full-frame imagery—some calibration data that doesn’t get much attention because you can’t use it to find planets—to get accurate long-term photometry of Boyajian’s Star over the course of the mission. Amazingly (to everyone but Bradley, I suspect), they found that the star got 4% dimmer over 4 years, in a monotonic but irregular way. What’s more it is the only star out of > 200 that show this effect.
In my opinion, this independent confirmation of the unprecedented effect Schaefer claimed—even if not covering the same time period—shows that Shaefer’s analysis is correct and the star really has dimmed a lot. Adding the two effects, the star is now apparently at least 17% dimmer than it was in 1890!
Where We Are Now
So what the heck is going on? We now have two inexplicable things going on: long-term, secular dimming of 17% in 115 years, and these days-long, deep “dips” of up to 22%. Both are very hard to explain.
Well, Occum’s Razor points towards a single explanation for both the secular dimming and the dips. Of course, in principle they may be unrelated, in which case Boyajian’s Star is extraordinary for two independent reasons. But I favor explanations that could plausibly cause both. At any rate, I’ve been engaging in a lot of “clean-sheet” reasoning lately, trying to cover all of the bases, and working with a lot of people to figure out what’s plausible. Steinn Sigurdsson, my often-time theorist sounding-board, is a co-author.
We decided that the explanation for the dimming must occur either at Boyajian’s Star itself (intrinsic variability), in orbit around it (circumstellar material), between the Sun and Boyajian’s Star (interstellar material) or in the Solar System (either between us and the star or in our instruments). In future installments, I’ll cover the observational constraints, including dip periodicities, long-wavelength constraints, and the brightnesses of nearby stars, and then go through each possibility and give it a plausibility.
Wait, What Did You Call the Star?
I’ve decided to call it “Boyajian’s Star“. Prof. Boyajian herself calls it the “WTF” star, ostensibly after the subtitle of her paper (“Where’s the Flux?”, natch). Early on during the media firestorm, a reporter asked me what I call it, and I admitted I could never remember its phone number and that within my group we called it “Tabby’s Star,” because she first showed it to us, back before it was published. The name stuck, and now that’s what it’s usually called.
I’m conflicted about that term. On the one hand, it has ensured that Tabby gets the credit for her work establishing how strange the star is, which is great (I wish I could claim that’s why I first used the term! It’s certainly why I kept using it). On the other hand, that name is actually the most common among professional astronomers, which is incongruous with other eponymous stars. You see, there’s a long tradition of naming stars after the people who made them famous—Barnard’s Star, Kapteyn’s Star, Przybylski’s Star—but professionalism and formality dictate that we always use the namesake’s surname. Not only does “Tabby’s Star” use her given name, it uses the diminutive form. It reminds me too much of one of the sexist double-standards common in academia (e.g. a man is “Prof. Smith”, but a woman is “Jenny”, especially from undergraduates!)
So, I’ve decided that when it comes to the professional literature, I’ll follow tradition and call it “Boyajian’s Star”. If other astronomers do the same, perhaps it will stick.
The paper is Wright & Sigurdsson, “Families of Plausible Solutions to the Puzzle of Boyajian’s Star,” and I’ll dribble out more about it in future installments until the arXiv posting.
Part II is here.
Update: By popular demand, Tabby has given us a pronunciation guide for “Boyajian”. She says “boy-AH-zhun”, with the j sounding like that in “Jean-Luc Picard” (that is, say “sh,” but use your voice, don’t whisper).