Is the anomalous star KIC 8462852 undergoing a long-term dimming or not? We’ve looked at Bradley Schaefer’s work on the star and the follow-ups disputing the idea from Michael Hippke and Daniel Angerhausen (NASA GSFC), with collaboration from Keivan Stassun and Michael Lund (both at Vanderbilt University) and LeHigh University’s Joshua Pepper. Dr. Schaefer (Louisiana State University) believes the evidence for dimming is still strong, and in the post below explains why. He has also provided a link to a more detailed analysis with supporting graphs and figures for those who want to go still deeper (further information below). As we embark on the Kickstarter campaign to put ‘Tabby’s Star’ in the sights of the Las Cumbres Observatory Global Telescope Network — an important project to which I have contributed and hope you will as well — we continue to monitor this evolving story. No matter how it turns out, the Kepler data are iron-clad, so the success of the Kickstarter campaign is vital to provide us with the further data we need to make sense of what we are seeing at this unusual star.
By Bradley Schaefer
The dips shown by KIC 8462852 (Tabby’s Star) are still a profound mystery. Further, I have found that Tabby’s star has faded by ~20% from 1890 to 1989 as measured from the Harvard plates. (This is now Schaefer 2016, ApJLett, 822, L34.) A straight line fit to the light curve gives a slope of +0.164 ± 0.013 magnitudes-per-century. The quoted error bar here is from the measurement error (as taken by a chi-square fit), whereas there is some larger systematic error associated with all the usual small problems in photographic photometry and the sampling of the plates.
To measure the systematic errors, I used 12 uncrowded check stars of the same magnitude and color as Tabby’s star, and all within ~22 arc-minutes. The average of the linear slopes is -0.007 mag/century, with an RMS scatter of 0.044 mag/cen. With the systematic error dominating, the century-long decline of Tabby’s Star is significant at the 4.0-sigma level (i.e., a probability of 0.000064 of such a high slope occurring by chance, even with systematic errors).
Two papers (Hippke et al. arXiv:1601.07314v4 & Lund et al. arXiv:1605.02760v1) have recently appeared with the basic claim that the historic light curves from Harvard (as part of the DASCH [Digital Access to a Sky Century@Harvard] database) have a much larger systematic error, more like ±0.15 mag/cen, with the agreed slope for Tabby’s Star then not being anything special. If the DASCH RMS scatter in the fitted linear slopes is really this large, then the existence of the century-long fading in Tabby’s Star would not be significant.
The two papers of Hippke and Lund have been widely publicized, because both authors have run to the press first. Indeed, Hippke contacted at least one reporter *before* he had submitted the first version of his paper. (At that time, Hippke had known about the existence of the Harvard plates for only two weeks, he had talked with zero people who had ever seen any archival plate, and Hippke still has never laid eyes on any archival plate.) In the usual way of ‘social media’, Hippke’s and Lund’s claims have been highlighted as a refutation of the century-long dimming, and this has been extended to everything about KIC 8462852. For example, on the first day of the launch of the Kickstarter program, the Reddit talk had the statement that the person ‘thought this has all been refuted’.
Well, despite ‘social media’, it is actually Hippke and Lund that are definitely wrong. As I’ll show, any experienced worker can quickly find exactly what mistakes they made, so that their claimed large scatter of slopes arises simply from two distinct mistakes on their part. But I have no ordinary venue to put out any effective counters or proofs. For example, any further submission to ApJ or ApJLett would not have any new data to show, and it would appear only many months from now. Research on Tabby’s Star is moving fast, so Hippke’s and Lund’s claims need to be challenged soon. The best way that I can think of to get the challenge and proofs out is to place them into a detailed document plus an email (*this* email), and to send this out to people who have queried me for an analysis of Hippke’s and Lund’s manuscripts on Tabby’s Star. A link to the detailed document appears below.
I present three reasons to show that Hippke and Lund have incorrect claims:
Reason #1: Hippke & Lund Both Made Two Killer Mistakes
Mistake #1 is that they selected many check stars that have some random nearby star at just the right distance so as to produce overlapping star images on the Harvard plates with large plate scales. The DASCH photometry uses SExtractor, and the algorithm returns something like the combined magnitude when the two star images overlap. This overlap produces an erroneously-bright magnitude for some plates. This occurs for most of the plates after the 1953-1969 Menzel gap (the Damon plates), resulting in an apparent jump across the Menzel gap. When the whole light curve is fit to a straight line, it will also result in an apparently brightening light curve.
Some crowding stars will cause this effect to be mainly visible on the RB & RH series or the AM & AC series, which result in the opposite sign for the jumps and slopes. In the linked PDF file below, I give many detailed examples, tables, and illustrations. That is, jumps in brightness across the Menzel gap and non-zero slopes are produced as pure artifacts of choosing check stars with nearby crowding stars. Now, critically, Tabby’s Star does not have any crowding stars. So it is not correct to choose any crowded-check-stars. No experienced researcher would make such a choice. It turns out that a large fraction of both Hippke’s and Lund’s stars with high claimed slopes are badly crowded. That is, many of their stars have high slopes simply due to this bad mistake.
Mistake #2 is that they have used the KIC magnitudes for calibration, rather than the APASS magnitudes as strongly recommended by DASCH in many places. The KIC calibration is based on the ‘g’ magnitudes as used by the Kepler satellite, whereas the APASS magnitudes directly give ‘B’ magnitudes. The native system of the Harvard plates is ‘B’. So the use of the KIC-calibration will always be problematic for some purposes because there must always be color terms needing correction. It is only a historical relic that the DASCH database allows the use of the KIC calibration. Yet most of Hippke’s and Lund’s results were made with the KIC calibration.
This actually matters. The reason is that the KIC-calibrated light curve for some presumably-constant star often shows an apparent slope (and possibly a jump in brightness across the Menzel gap), whereas the APASS-calibrated light curve for the same star shows a perfectly flat light curve. I show several examples of this effect in the attached PDF file. With this, we see that the use of the KIC-calibration by Hippke & Lund is causing the jumps and slopes as pure artifacts. Their Mistake #2 would not be made by anyone experienced with the Harvard plates (or anyone who reads the DASCH website or papers).
The attached PDF file gives a detailed account of the commission of the errors. Between the two killer mistakes, all of Hippke’s and Lund’s claims are shown to be artifacts of their bad analysis.
Reason #2: Two Measures by Experienced Workers give ±0.044 and ±0.048
Measure #1 is by myself, as given in fine detail in my ApJLett paper. I derive the century-long slopes for 12 uncrowded check stars that have essentially identical magnitude, color, and position as Tabby’s Star. Whatever systematic and measurement errors happen for Tabby’s Star on the DASCH photometry, the identical effects must be present on these 12 stars. No one can do any better than this for a direct measure of the real total errors. With this, the average slope is very close to zero, while the RMS of the slopes is ±0.044 mag/cen. The largest deviation from a flat slope is one at -0.070 mag/cen. I should mention that I have a vast experience with the Harvard plates, with nearly continuous work since 1979, something like 50 papers in refereed journals, plus five papers on the theory of photographic photometry.
Measure #2 is by Josh Grindlay. He is a professor at Harvard; he has been a long time user of the Harvard plates (going back before 1979), and he is the founder and leader of the DASCH program. He had long been using DASCH light curves, so he knew perfectly well that DASCH produces flat light curves for constant stars. With the spectacle of Hippke’s paper, he started a formal measure of many Landolt stars with the DASCH data. (Landolt stars have long served the community as standard stars, and they are most likely closely constant in brightness.) For 31 Landolt stars, Grindlay finds that the average fitted-linear-slope is -0.015±0.048 mag/cen.
So we have the two most experienced workers in the world, and we are getting an RMS in the fitted-linear-slope of 0.044-0.048 mag/cen. For Tabby’s Star, this results in the century-long dimming being near 4.0-sigma in significance. I think that these two solid measures by the most experienced people in the world are to be strongly preferred to a claim coming from people who have yet to lay eyes on any archival photographic plate.
Reason #3: The Dimming of Tabby’s Star Has Been Confirmed
Ben Montet is in the process of investigating the long-term photometric behavior of KIC 8462852 in a high quality independent data set, and his preliminary results support the finding that Tabby’s star is indeed fading.
Tabby’s Star is bright, and the Kepler data is legendary for its photometric accuracy and stability. If Tabby’s Star is fading at the rate of 0.164 mag/cen (which it might or might not still be doing), then it should have faded by 0.0073 mag over the Kepler lifetime on the main Cygnus Field. This should be discoverable by a careful analysis.
Apparently Montet has made such an analysis, and finds Tabby’s Star to be fading at some unspecified fade-rate. So we have an apparent confirmation of the fading of Tabby’s Star over 4.5 years, although certainly we must await a definitive paper coming from Montet. [A group at Pulkova Observatory has claimed to provide a weak confirmation of a fading of Tabby’s Star. This is based on just ten plates from 1922 to 2001.There is indeed a formally fading slope, but the real uncertainties are greatly larger than any claimed slope. This result is not a confirmation.]
For those interested in following this matter further, the document I discuss above, my “ANALYSIS OF HIPPKE et al. (2016) and LUND et al. (2016) is available.” Often the refutations of claims are not short, so I have presented the full details in this document. In sum: We have three strong reasons to know that Hippke’s and Lund’s claims are certainly wrong.
Reason #1 is very compelling and it will be interesting to see if this is rebuttable. Reason #2 is not as persuasive. Scientific conclusions shouldn’t rest on expertise per se. They should rest on data. An explanation of how that expertise translates into quality of data would be nice, but that is probably a lot to ask in this kind of venue.
Did you miss the link to the PDF at the bottom of the article? I’m not sure how he could make either issue more clear. It’s not a matter of expertise per-se but experience with the data set and its subtle quirks which he comprehensively documents in the PDF.
Thank you. I went back and read the PDF, and the DASCH explanation was understandable. I can see now what Prof. Schaefer meant in concrete terms when he mentioned experience. The second explanation was a little over my head. A muscular presentation and in my own lay view the burden of proof has shifted to Lipke/Lund. Do you think they should retract their conclusions if they can’t adequately explain why the relevant algorithms seem to produce poor measures for so many of their check stars?
In any case, KIc 8462852 is a remarkable star and it’s explanation will be remarkable. I wonder how many other rare and new phenonema are yet to be discovered with future “big data” observation tools like Keppler.
So where does this leave us? The question of a century long dimming seems to have become a nasty academic debate, with rank pulling added to the mix of claim and counter claim.
If the long dimming is correct, this appears to rule out a comet hypothesis due to the sheer number of comet objects required. OTOH, it does nothing to support the idea of an advanced ETI presence either, other than the speculations of a century long construction of large orbiting structures.
So KIC 8462852 remains an enigmatic object. We need more observations to try to understand the observed phenomena, and dare I say, more light rather than heat shed upon this mystery.
If there is one thing I have learned from the discussion and debate around Tabby’s Star is that aliens are still scary to many, especially professional scientists. Even ones building a megastructure around a star 1,500 light years from Earth and paying us no heed so far as we can tell.
Oh I am sure what is happening around that distant sun probably has a natural cosmic explanation, but why am I so skeptical of a fleet of giant comets as the leading contender?
When it comes to ETI and humanity’s perceived place in the Universe as a result, Voltaire had it pegged way back in 1752:
http://wondersmith.com/scifi/micro.htm
Afraid of aliens? Really?
Evidence for aliens would be a major discovery, and it’s not one you’d want to get wrong: I reckon it would receive fairly major news coverage so your name would end up associated with it so you’d probably find it fairly hard to shake the “scientist who got it wrong about aliens” tag. Consider when Dr Felisa Wolfe-Simon will stop being associated with the “arsenic life” nonsense, and that’s far less of a media-friendly type of discovery. So I find it quite understandable that scientists are looking into alternative possibilities and are rather hesitant to claim the existence of aliens before the evidence is solid.
This contrasts with a fair number of commentators I see on internet astronomy sites who leap to aliens as being the explanation for just about any observations that appear to be even slightly unexpected, who will nevertheless most likely not end up having their names splashed about all over the media in relation to their claims.
What I find interesting is you take the “Afraid of aliens? Really?’ approach and then proceed to give a good reason to be afraid of claiming “Aliens”.
Again, I make no claim of being a scientific genius, only an interested layman…and a certain student of history. My thought all along has been such a discovery, a discovery that might well imply a centuries long construction effort, will do two things: 1) bring out every kook in crackpot land , and knowing this, 2 ) will throw up a wall of resistance from the scientific community, BASED ON FEAR of just what you mentioned concerning “arsenic life”. At that point, given the very human fear of an embarrassing mistake I find myself not fully able to trust the so-called “Objective” scientist to truly be objective. And I do believe the result will be to torture and twist any natural explanation to stretch and fit over what, in the end, NOBODY really wants to take the chance of calling.
Now I have no idea if this is an alien megastructure or the largest collection of comets in the known universe, or if we’ve found Never-Never Land. I do know I’m not trusting either side to be really objective about it, but least of all to make the call that it MIGHT be the greatest discovery in history. There’s always going to be uncertainity. And while human ignorance may be infinite, human courage is not…especially in THIS…
As has been pointed out, the chances of a nearby ETI building large structures in just the century we happen to be observing the universe are vanishingly small, unless we are completely wrong about our models for alien civs.
The claim to have found a contemporary alien civ would have huge impact, and therefore it makes a lot of sense to have that claim confirmed rather than be in error. At this point all we have is some data about deep dips in the luminosity and some possible data on long term dimming. To jump to the conclusion that this is an alien megastructure rather than a natural explanation is premature, to say the least. This is so reminiscent of craetionists jumping on every “unexplained” natural phenomena as being proof that god exists, or that flying saucers are real, rather than mis-identifications.
In my time I well recall the announcement of aliens based on what turned out to be pulsar emissions. We need a lot more data on this star to both confirm the observations and to find different types of observations to characterize the phenomenon rather than speculating, however fun that might be.
Don’t worry, I remember that too. (Pulsar = LGM), and nowhere do I jump to any conclusions I’m not trained to make. But I also mean, and standby what I said, I question and doubt the intellectual courage for most scientists to make THAT jump. I’m hardly a Creationist of any stripe and have done battle way too often with them as it is.
BUT, the kooks are already sliding out of the woodwork, including at least one “I was abducted by them and saw it all” claim. As far as jumping to conclusions about every cosmic mystery and claiming it’s Klingons, what about jumping to the conclusion its NOT aliens? And who, if anyone, has the guts to say it and stick to it in the face of such nonsense?
Heck, even if I was a scientist and able to make such judgments on this topic, I’m not sure I would risk the slanders that would result even if I was RIGHT. And I’ve hit a lot of flying saucer believers over the head with that…
So, I have no confidence in most scientists having the ‘nads to do it, even if they know it’s true…
The classification of type I, II, III civilizations is wrong in a way that type III never existed in this universe hence there is a need to redefine type I & II (base on the amount of intelligent computational usage rather than energy). If we have another world war, this technological civilization might take a long time to come back to the current level or might not, Vernor Vinge said something similar to this. The temporal yardstick is much bigger than most of us realize since we only pay attention to the spatial one.
As someone in this forum has already pointed out, we labeled several stars as “the most interesting star in this universe” time after time, this is a matter of when not if it somehow happens turning out to be true in the future even though this “future” might be next decade or next century who knows; an example of crying wolf?
Well those are fears of two different things, are they not?
You also miss the motivation of getting credit for a correct discovery, which is also as important: being associated with the correct claim is guaranteed positive fame, even as being associated with an incorrect claim can bring negative fame.
As an example, consider the discovery of the hot Jupiter orbiting 51 Pegasi, a planet that was a complete surprise (hot Jupiters had been considered as a possibility by Otto Struve in 1952, though before the actual discovery this paper seems to have received rather little attention). The discoverers did quite a lot of work to rule out other possible causes of the observed radial velocity variations before making the claim that they had discovered an exoplanet around a solar-type star. They were cautious to make sure their claim was correct, but they certainly didn’t avoid ever making the claim that the planet was there, despite the risk that if they were wrong then they’d be associated with a false claim of an exoplanet.
andy said on May 24, 2016 at 17:13:
“Afraid of aliens? Really?”
Yes. Really.
The general public is often much more direct and even, dare I say, openly honest in their views and feelings on alien life – especially the intelligent type that could reach Earth. The point here is not whether their views and feelings are ultimately accurate; what matters in this case are their honest reactions, which are usually those of either fear or almost literal worship.
For them aliens are either marauding invaders or godlike saviors, with little variation in between.
Scientists and leaders take a different tack, even though they are no less human than the people they are supposed to serve. They often use their positions to publicly dismiss the idea of alien life (especially the kind that could come here) while simultaneously saying there probably is life beyond Earth, only it is really far away, etc. After all they do not want to appear to be totally behind the times.
What the second group is usually concerned about varies, but it is often trying not to look like fools and ruin their careers in the case of professional scientists (note that many SETI scientists are either tenured or retired so they are considered safe – not all but many. And note I am talking about SETI not those who search for exoplanets – that has been totally safe professionally since 1995). Aliens of course will become totally acceptable to this group on the day they are discovered and confirmed. It will be especially amusing to watch all the scientists come out of the woodwork to declare that “they knew it all along!”
The leaders – be they secular politicians or royalty or the clergy or the military – are mainly concerned about staying in power. The thought of beings more powerful than they, excluding the already established supernatural deities (whose images and words they can control for the masses), who could arrive at any moment with superior knowledge and weaponry (as well as the literal high ground) is too frightening a thought to such people who want to be in control of everything all the time. Better to either dismiss such concepts as either childish fantasy or pretend they can handle any threat any where any time. And pray that the masses they rule still think alien invaders will come in the form of warriors with laser rifles rather than, say, dropping a few planetoids on our heads for which we are still currently defenseless. Aliens who want to destroy our species and take Earth for themselves do not need fancy weapons, just a few well-aimed space rocks (which can be maneuvered with relatively simple rocket engines).
So in conclusion, yes, there is a lot of motivation due to fear. Which most of those in power (professional scientists included) would not want to publicly admit. Whether it is ultimately right or wrong, our views on the subject affect our ability to find ETI, both good and bad.
ljk said
“…still think alien invaders will come in the form of warriors with laser rifles…”
So Will Smith and Jeff Goldblum didn’t film that 1996 flick ‘Independance Day’ as a documentary? Awww. (Tee hee) ;)
Actually if you read Stephen Hawking’s ideas on ETI coming to Earth, it seems to be taken directly from the plot for Independence Day so you may not be far off.
See here:
https://centauri-dreams.org/?p=14703
And especially here:
https://centauri-dreams.org/?p=14754
ljk, I actually get the opposite impression from the Tabby’s Star debate. While I agree many scientists still avoid discussing aliens like the plague (and Schaefer never mentions them, and Hippke only dismissively), I’m getting the feeling that an increasing number are beginning to find it more ‘acceptable’ to discuss aliens, or at least discuss topics to which aliens have been associated, like Tabby’s Star. Certainly astrobiology and exoplanet science and the continuing hunt for habitable worlds has helped, but look at the headlines discussion of Tabby’s Star gets, not just in the wacky tabloids, but in far more respectable publications as well that may not have run those kinds of stories in years gone by. I think scientists are starting to see that and it’s encouraging them to speak out more about these kinds of ideas. Speaking as a journalist it does feel like in the last year or two that there’s been more press releases and more scientific papers being publicised about alien life and SETI than before. The subject doesn’t seem to be as taboo as it has in the past and that can only be a good thing in the long run.
Oh I admit there is a thaw starting to show in regards to aliens when it comes to the professional science cliques – and it will burst wide open when proof is found as everyone will want credit for having known it first all along. But still more often than not, unless one is very careful, the subject of aliens is one not to be broadcast or discussed haphazardly. One can still incur both ridicule and career suicide. This is only the year 2016 after all.
That is one big reason why the idea of “hiding” evidence of ETI makes little sense: People in general are aware of the concept of aliens at least, so it won’t be a complete culture shock as it may have been just a few centuries ago.
As for the professional scientists, the one (or ones) who do find extraterrestrials, be they microbes or Dyson Shells, will be instantly famous, rich, in the history books forever. Granted there are some who shun the limelight but they seem to be an increasingly endangered species in today’s society.
It’s been a year, no ideas (so far, that may change very fast).. virtually every natural cause has been ruled out. Leaving just one.
Jason Wright noted that it will most likely be a process of elimination rather than discovery.
So the final “product” will be “we ruled out everything else, so it most likely has to be this” .
That’s the best we’ll get for a while until new data comes in.. and it will get better as time goes as the new generation of telescopes come online.
Two Questions for Dr Schaefer: ONE: I have looked at the KFFI for KIC8462852 ONLY(i.e. not any OTHER star in the kepler field). I saw a signifigant dimming trend and posted a comment on it, but another reader commented, saying that this trend is evident in the RAW DATA for all Kepler stars, and is just an artifact. I presume what Ben Montet did was REMOVE this artifact from the raw data,but then he saw a residual dimming over the 4.5 years of the dataset. Is this correct? TWO: Dirk Bontes posted a comment on April 28, 2016 at 16:15 in Paul Gilster’s post: KIC8462852: A Century Long FADE? He postulated that ALL of the dimmings can be attributed to the ionization of Helium INSIDE the star blocking some of the light. I challenged him on whether this process could ALSO produce a century long fade as well as all of the lightcurve FLUCTUATIONS, but he said it was not a problem. Assuming that this process DOES go on in a star AT THE PRECICE POINT of transfer of a main sequence star to a subgiant star, could ALL stars fade IN THAT VERY BRIEF time period BEFORE they start to BRIGHTEN after becoming full-fledged subgiant stars?
Harry R Ray,
Yes, stellar luminosity can be affected by Helium ionization, but not in
the way described in the comment. The cycle of Helium being ionized and then gaining
back an electron (recombination) leads to the star pulsating. Stellar
pulsations will cause to the brightness to vary in a very regular way and these
stars are the Cepheid variables. Cepheids vary in brightness in a way
that is not at all like what we see in KIC 846852. Furthermore, Cepheids
have masses in the range of ~3 to 9 Solar masses while those for F dwarfs like KIC 846852 are in the range of ~1.4 to 1 Solar masses which below the minimum mass needed for this
process to occur. For more see:
http://ned.ipac.caltech.edu/level5/ESSAYS/Evans/evans.html
Hope this helps.
David B: Have you read Dirk Bontes’ 2000 word essay on this subject? In it he states that the “Cepheid” rules you mentioned above do not apply to KIC8462852 because KIC8462852 is NOT a Cepheid. This is why I requested a response from someone LIKE Dr Bradley Schaefer with knowledge enough to refute Mr Bontes claims. Intil this happens, I assume Mr Bontes is correct. I am not alone in this perception. Other readers have come to the same conclusion.
He conflates valid scientific theories (kappa mechanism, e.g. opacity changes in the partial ionization zone as a valve mechanism) with nonsense (polarity changes a the cause of pulsation). Changes in the ionization levels has nothing to do with the magnetic field of the star. And then adds some handwaving (changes are “reminiscent” of Chepheids, so it must be similar, even though he just concluded that the star is not a giant/supergiant and its close to the delta Scuti-gamma Dor variables instead). So…. nope.
Just to make things clear: pulsation occurs, at least in the classical instability strip when the partial ionization zone(s) of H, HeI, and/or HeII are in the right depth, e.g. not too close to the surface (hot stars), and not too deep where/when convective motions can kick in an transfer energy instead of radiation (colder stars). In this region, radiation coming from below runs into a layer when less ionized particles start to populate the star. Their larger cross section traps the radiation and turns it into heating, thereby expanding the star, and ionization. When enough atoms are ionized, the opacity drops, and radiation can pass through, leading to cooling and contraction, as well as electron captures, populating the layer with atoms again. Then the whole process restarts. As you can see, there is no magnetic field involved.
But this is cyclic, to the point of _clockwork_ precision. And _very_ strongly depends on the stellar structure, especially the periods. So if the star is near the A-F stars around the main sequence, it can _only_ oscillate in delta Scuti and gamma Doradus-type periods. There will be no century long dimming by slow buildup of less ionized atoms causing larger opacities, that is fully against stellar pulsation theory.
By the way, pleople did search pulsations in Tabby’s star, but to my knowledge the conclusion was that it doesn’t pulsate, and the small-amplitude periodic variation (not the dimmings!) comes from stellar rotation, e.g. starspots.
Dirk Bontes: Please respond to LasloB! Otherwise, it appears your argument is off the table. If that’s the case, this is where we are now. Either it’s comets(but ONLY if there is NO fade, AND EXPERTS can come up with a NATURAL MECHANISM that would cause a “megacomet” or Centaur to produce a lightcurve RESEMBLING the “Q8”), or, if there IS a fade, it is either an internal process of which we have ABSOLUTELY NO KNOWLEDGE RIGHT NOW, or, it is GAS generated by a GRAZING COLLISION(very, VERY contrived, but possible) between KIC8462852 and the PUTATIVE red dwarf companion, or, FINALLY, a megastructure being CONSTRUCTED in an INCREDIBLY SHORT PERIOD OF TIME!
@Harry R Ray
Ithink you ought to get your keyboard seen to, the CAPS LOCK key seems to be sticking.
We have been there before, he is not going to change.
Otto:
Harry uses caps to EMPHASIZE words. It can NOT be done otherwise on plain text appearing. It does draw the eye, and I have to admit that when I see his comments I’m immediately drawn, hopefully NOT to the exclusion of others.
Be that as it may, I have to say one of my all time favorite personalities in astrophysics has got to be Sir Fredrick Hoyle. And when Harry comments, I see in my mind’s eye Sir Fred.
Harry:
It is a compliment.
Wow, thanks for the astrophysics 101 :)
LaszloM “Just to make things clear: pulsation occurs, at least in the classical instability strip when the partial ionization zone(s) of H, HeI, and/or HeII are in the right depth, e.g. not too close to the surface (hot stars), and not too deep where/when convective motions can kick in and transfer energy instead of radiation (colder stars).”
So, when the zone is not at the right depth, no pulsation occurs, despite an ionized layer being present. So a star can have an ionized layer – and therefore block light – and not pulsate.
LaszloM “In this region, radiation coming from below runs into a layer when less ionized particles start to populate the star. Their larger cross section traps the radiation and turns it into heating, thereby expanding the star, and ionization. When enough atoms are ionized, the opacity drops, and radiation can pass through, leading to cooling and contraction, as well as electron captures, populating the layer with atoms again. Then the whole process restarts”.
This is not correct. In a star photons find their way by being captured by and exciting an electron that orbits some nucleus, like a proton. When next the excited electron returns to a less energetic orbital, it re-emits the photon. Consequently, if nuclei are fully ionized, having no electrons in orbit at all, this process cannot occur. If a layer has many of such nuclei – all orbiting the magnetic field lines of the star – then a proportionately diminished number of photons will be able to pass through that layer. Since the energy of the blocked photons cannot escape from the star, it builds up, accumulates and this causes all of the interior mass enclosed by the fully ionized layer to expand, as well as the ionized layer itself as well, which will also become thinner, since its radius increases. Consequently the photon blocking nuclei move further apart, enabling the photons to pass between them more easily and to escape from the star.
LaszloM “But this is cyclic, to the point of _clockwork_ precision. And _very_ strongly depends on the stellar structure, especially the periods.”
Sure, but even though in Cepheids it occurs with clockwork precision, there is no such thing as a perpetuum mobile. Even in Cepheids some energy must be expended to keep it going.
LaszloM “By the way, people did search pulsations in Tabby’s star, but to my knowledge the conclusion was that it doesn’t pulsate, and the small-amplitude periodic variation (not the dimmings!) comes from stellar rotation, e.g. starspots”.
I have never said that KIC8462852 pulsates. In fact I asserted that it is not a Cepheid.
As for the sunspots, I do not know that they have been observed. My understanding is that KIC8462852 shows no exceptional magnetic activity.
Harry R Ray “TWO: Dirk Bontes posted a comment on April 28, 2016 at 16:15 in Paul Gilster’s post: KIC8462852: A Century Long FADE? He postulated that ALL of the dimmings can be attributed to the ionization of Helium INSIDE the star blocking some of the light. I challenged him on whether this process could ALSO produce a century long fade as well as all of the lightcurve FLUCTUATIONS, but he said it was not a problem”.
Quite. At first I was surprised by the century long dimming. But since the twenty percent dips to me indicate a strong, magnetic field, reversing in a catatstrophic change of state, we may deduce that the century long dimming is due to the strength of this magnetic field gradually increasing. This suggests a spin up of the star – and we already know that compared to our sun it does rotate relatively fast.
So what might cause the spin-up of this star? According to the law of conservation of momentum it must be due to a contraction of the star: it is growing smaller – and that contraction again might contribute in some part to its century long dimming.
Harry R Ray: “Assuming that this process DOES go on in a star AT THE PRECISE POINT of transfer of a main sequence star to a subgiant star, could ALL stars fade IN THAT VERY BRIEF time period BEFORE they start to BRIGHTEN after becoming full-fledged subgiant stars?”
I agree. I seem to remember that I elsewhere have stated that the lack of helium in the star’s atmosphere surprised me and that it suggests that this is a low mas star that is about to evolve into a red giant and that the reason that the helium is not detected, is because its helium flash, in which it burns all of its helium, has already occurred.
Every star on this evolutionary path has to experience the same phenomenon.
Is this hypothetical contraction caused by the volume of carbon produced by the helium flash being smaller than the volume of helium before the helium flash? That would cause matter in the higher layers to fall down, causing an increase in the gravity that the plasma in those higher layers experience, which in turn results in the plasma in those layers gradually being compressed, causing the star to contract and to spin up.
It is a joy to learn the new things about stellar evolution that this star demonstrates and teaches us.
Who would have guessed before this star was discovered? (Well, I might have, but since I never considered it, I didn’t.)
Dirk:
So, if I may, and I am NO astrophysicist…. here are some possible predictions if your hypothesis is correct.
(1) Tabby’s Star spin should be increasing. Unsure if this would be detectable.
(2) The star should be contacting as related to dimming and brightening (and expanding?) …possibly detectable by radial velocity?
(3) We should expect find a handful of other stars exhibiting similar behavior if we comb through the Kepler data. Anything greater than 5% dimming, (MUCH larger than a planet) and non-periodic, would be suspect.
(4) When we are finally able to grab a spectrum…. We should expect to see significant Helium absorption lines when the star dims, as the Helium is ionized, followed by Helium emission lines as it returns to normal brightness.
1. Indeed, I expect the spin to increase.
2. I do not quite understand your 2, but I think that the star is contracting and this decreases the surface area we see and thus ought to contribute to less light being emitted. We see essentially the same in pulsating Cepheids: when they swell up, they put out more light because of their larger surface, and vice versa. This contracting must have contributed to the century long dimming found by Schaefer.
3. I do not know if there is sufficient Kepler data to discern one or more other events of such century long dimming partly due to contraction with any significance. Perhaps the Harvard plates would offer a better chance of finding another similar star – if the Schaefer’s process can be automated.
4. Well, since no helium is observed in KIC8462852, I rather suspect that its helium has been consumed in the helium flash. So I expect that its ionization layer consists of completely ionized hydrogen.
Ah, you mean the 750 day period dip. I now think that there is no helium at all present in the star, but let’s say there is. Then during the dip it would be completely ionized and therefore be unable to absorp any radiation. Therefore no helium absorption lines – or in any case less absorption lines – would be present during the dip. There would be reduced helium emission lines, which would return to normal after the dip. If helium is at all present. But we also have to consider that the hypothetical helium ionization layer will be at depth. How much of the light emitted at that depth will manage to get to the surface of the star and be emitted into space to be detected by us? As I understand the process, we can only detect light that is emitted by electrons in the surface layer of the star; anything else, deeper in the star, will be absorbed and re-emitted, usually by electrons orbiting a hydrogen nucleus. Right?
Dirk:
I think it is a great idea, and you should pursue with all haste, to get your idea published as a scientific paper so that credit is given to you assuming you are correct.
You stated “…I now think that there is no helium at all present in the star, but let’s say there is. Then during the dip it would be completely ionized and therefore be unable to absorp any radiation. Therefore no helium absorption lines – or in any case less absorption lines – would be present during the dip. There would be reduced helium emission lines, which would return to normal after the dip…..”
I still say that leading INTO a dimming event, and probably during most of the dimming (several days?) there should be absorption lines, of Helium, or perhaps Hydrogen. These absorption lines should go away and be replaced by Helium/Hydrogen emission lines as the star comes out of it’s dimming event and returns to “normal” as predictions to support your hypothesis.
Dirk: Thanks for the additional details, but what I really want you to do is REBUTT LasloM’s refutations LINE BY LINE(by which I mean: LasloM said THIS[“……….”] about my theory. In response, I say that he is wrong because[“….”]. Then, I would ask LasloM to respond to your RESPONSE, and so on, like Schaefer and Hippke have been doing. Then, when all arguments have been posted, I would like Paul Carr to ask BOTH Schaffer AND Hippke for THEIR take on your arguments, so that I(and OTHER READERS) who have far less expertise than either you or LasloM in this field can come to some sort of DEFINITIVE CONCLUSION on this matter!
Um, I do am pressed for time. I have a deadline to keep, translating 27k words from German to Dutch during the next couple of weeks, as well as other pressing obligations. But I will keep it in mind.
Yesterday I wrote to the Anton Pannekoek Institute and asked them for help and guidance in rewriting my article for a scientific publication. I have not yet received a reply.
My article is based on ideas about electric currents and the solar magnetic field and those of the planets and the effect of magnetic fields on bodies – like planets – moving through magnetic fields, that I developed between 1997 and 2000 in the various edtions of my astronomy book and applied ten years later in several articles in Dutch published on the Internet and two other astronomy articles published at Smashwords, and one long article that I started on three or four years ago and as yet have to finish. These past fifteen years I actually have scarcely occupied myself with astronomy.
In those days I heard astronomers say that electricity is not a force that is relevant for astronomers and astronomy. Gravity, gravity, gravity! was their slogan. I had been writing the various editions of my astronomy book and I knew and know that electricity is extremely relevant for astronomy, using it to explain many phenomena in astronomy and geology. There cannot be magnetic fields without an electric current being present, which in essence is one or more charged particles moving through space.
Actually, there is not much to respond to what LaszloM said. I have addressed most of it already.
What I did not address was this:
LaszloM has said: “He conflates valid scientific theories (kappa mechanism, e.g. opacity changes in the partial ionization zone as a valve mechanism) …”
I do not need to address this, because LaszloM said it is valid.
and LaszloM said this: “…with nonsense (polarity changes a the cause of pulsation). Changes in the ionization levels has nothing to do with the magnetic field of the star”.
So this is at issue, science – electricity and magnetism science that astronomers as yet consider mostly irrelevant – as not known to physicists.
I will try to keep this simple. It is agreed upon that in Cepheids (and in other stars at depths that preclude Cepheid pulsations) there – at least sometimes – occurs an ionized layer, ie.e a layer that has an electric charge. Since celestial bodies are electrically neutral, somewhere else the star must have an equal opposite electrical charge.
Now Cepheids pulsate, their radius increasing and decreasing. The law of conservation of momentum dictates that when the radius of a body decreases, it will spin up, and vice versa it will spin down if its radius increases. (Consequently non-complex red supergiants will scarcely, most likely not at all rotate, since they have an enormously increased radius.)
Therefore, Cepheids will rotate at least part of the time. (This argument is just to establish that Cepheids experience rotation.)
Now if Cepheids rotate and if they have a layer in their atmosphere that is electrically charged, then we have electric charges moving through space, i.e. we have an electric current. In fact we have two electric current with opposite charge, one at the radius of the ionized layer and a current of the opposite charge that moves in the smae direction at another mean radius (for these opposite charges rotate in the same direction as the charges in the ionized layer).
An electric current evokes a magnetic field, and opposite currents evoke magnetic fields with opposite direction. It is getting more complicated, isn’t it?
If I recall correctly, I developed my model for the solar magnetic field, which is rather soimilar, already in the very primitive Dutch first edition of my astronomy book, in 1997. (Which is only of interest to historians of science, for it is extremely unreadable; in fact I did not comprehend a lot of what I had written when I later translated it into English, which resulted in an improved English version.)
In that first Dutch edition I had already described the pulsations of Cepheids, as my focus was on Mira type variable stars, which astronomers erroneously believe to be rather similar to Cepheids.
For solar polarity reversals to occur, in my model the pair of positive and negative currents in a star must switch places in a catatstrophic change of state. (The magnetic field dissolves and then is rebuild.)
So, to keep it simple, the mean radius at which both currents are present in a star must change cyclically.
It only later occurred to me, I believe in the so far final third English edition of my astronomy book, as a hypothesis, that this change in the radius of one of those currents – actually in the change of the radius of the electrically charged particles – might explain the sudden ionization of the Cepheid ionized layer. If this layer is initially electrical neutral and there is such a cyclical movement in the radius of the electric current, then the arrival of these charges would suddenly and temporarily ionize that layer.
I do not know if in fact this occurs, but as conceptual science, as a model, it does make sense. So I added that idea as a hypothesis for the ionization of this layer in Cepheids in 2000 to my book. And since my article about KIC 8462852 consists mostly of Cepheid quotes from that book, that hypothesis is included as well.
And LaszloM said this “And then adds some handwaving (changes are “reminiscent” of Chepheids, so it must be similar, even though he just concluded that the star is not a giant/supergiant and its close to the delta Scuti-gamma Dor variables instead)”.
Well, yes it is reminiscent to what happens to Cepheids, because Cepheids too do dim.
Those who have read my article about KIC 8462852 will have noticed that I have not wasted one word on any hypotheses that are external to the star, except for mentioning the lack of infrared radiation and discussing its companion red dwarf star. My conclusion was that there is nothing of relevance outside the star, so refuting hypotheses that are external to the star is a waste of effort.
I believe that someone in this thread has already quoted Sherlock Holmes: “If one has eliminated what is possible, what is improbable must be true”. Similar adages are the application of Occam’s razor, and Albert Einsteins assertion that solutions ought to be simple, but not too simple.
In Cepheids we have a known mechanism for the light inside a star to be blocked. (If anyone knows of another mechanism for light inside a star to be blocked, please tell me.)
This known mechanism suffices for me to explain the 750 day period dimming by twenty percent of the star – by a sudden ionization of a layer within the star – as well as the century long dimming (by a gradual increase of the magnetic field strength; in combination, as I later realized, with the contraction of the star).
I also know that heat is released when the polarity of a magnetic field reverses. I have also written quite a lot about such polarity reversals in the catastrophic change of state of various magnetic fields, explaining various astrophysical phenomena by them.
There is no doubt in my mind whatsoever that the dips with a 750 day period are due to the polarity reversal of the magnetic field of KIC 8462852.
As for the other, irregular fluctuations in the light output of KIC 8462852, I would rather not speculate about such chaotic behavior – because I have no confidence in such speculations at all.
GOTCHA: Waiting for LasloM’s reply. The only thing left that confuses me a bit is what GENERATES the magnetic field that GENERATES this process you talk about. Daniel de Franca Deniz Rocha has proposed that the cause for the short-term dimmings and the long-term fade is a collision in the past with either a very HIGH-MASS Super-Jupiter or a very LOW-MASS Brown Dwarf in a way that produces the INITIAL spin-up of KIC8462852 and MAYBE the magnetic field of which you speak. The only issue I have with his theory as a STAND-ALONE theory is that a RECENT collision would have produced a CHANGE IN THE SPECTRA of KIC8462852 resulting in it NO LONGER BEING an F3V star. BUT: if the collision happened much further in the past, KIC8462852 would have had time to quiet back down to an F3V star, and the continued fading could be an effect of BOTH YOUR AND HIS proceces. When you have time, please read his theory near the BOTTOM of this comment page and comment on it.
Just a question on identification of the star, is APASS J200615.5+442725 the identifier for KIC 8462852? So far it doesn’t look like the APASS catalogue is in SIMBAD.
So lets recap this once more. After almost a year of various attempts to refute the dimming, and comets flying all over their system we havve … advanced in our under … standing precisely … ah lets see…zero! … for the Tabby anomaly. Perr..haps we should do some modeling for an alien mega structure that can explain well the the the … possibility that … well you know!
I know you must ALL be sick of this, but here I go again! Model a REALISTIC “Alien Megastructure” that would fit the “Q8” lightcurve PERFECTLY and ELIMINATE ALL OTHER CONFIGURATIONS and I am ALL IN!
http://www.science20.com/indepth_analytics/blog/the_real_reason_why_the_kic_8462852_comet_hypothesis_is_dead-167340
…Jose Solarzano seems to capably stick a fork in the comet hypothesis for Tabby’s dimmings, at least as an explanation for the for the Day 800 (aka “Q8”) dimming.
http://www.datasciencecentral.com/profiles/blogs/kic-8462852-models-of-transits
…And then Jose proposes a Niven Ring as the best model I have seen to explain this same dimming event.
Jose Solarzano’s expertise lies in computer generated models for GENERAL light curves, but NOT in astronomy(and therefore astronomical OBJECTS)per se. Maybe this is why many in the astronomical COMMUNITY(like Bodman, Quillan, and Jason Wright) have been reticent to respond(either positively OR negatively) to his ideas. I am STILL holding out hope that they will SOON, instead of exhausting ALL POSSIBILITIES of the “Q8” light curve being either the result of a SINGLE giant “megacomet”(as Einiac suggests)or from gas(NOT dust)generated by a COLLISION between KIC8462852 and its nearby PUTATIVE companion star.
EXACTLY! And that’s the one thing no one will have the courage to do. Try to model the incredible and see how it works. You get down to basics, a lot of human LIKE the idea we are alone in the universe. It makes us SO MUCH more important and unique.
The problem here is that with enough torture, you can indeed create a number of viable artificial explanation models, but they will have no new data to test predictions against. In that sense, it is mathiness.
I wonder if we have enough data to get a meaningful estimate of a second derivative over the century. Whatever process is causing this might be speeding up or slowing down.
I imagine that is not possible with the error bars of the existing data set. There isn’t even consensus that the first derivative is non-zero.
ljk, the idea of a Dyson sphere being built/decaying about right next door, right when we start looking, in what looks like an otherwise empty Universe doesn’t unease you at least a little bit?
If it really is aliens, either they are related to us somehow or a very thorough Great Filter is right in front of us. Otherwise, the odds for it to be a coincidence are beyond astronomical, unless for some reason technological life just started being possible.
If they are related to us, they are one massive unknown, and there is absolutely no guarantee they are benign.
If they aren’t, well, that whole humankind thing was fun while it lasted. Also we should find more decaying Dyson spheres across the galaxy in the future.
If technological life just started, it means we missed something big about it/the Universe, but things may become very interesting.
I expect it to be anything but a natural phenomenon anyway, like pulsars did, but one never knows…
And natural or not, pointing more telescopes on it is a good idea.
Eth said on May 24, 2016 at 19:23:
“ljk, the idea of a Dyson sphere being built/decaying about right next door, right when we start looking, in what looks like an otherwise empty Universe doesn’t unease you at least a little bit?”
Should it? I mean, what are we as a collective species supposed to do if it is an ETI building a Dyson Shell? One that is almost 1,500 light years away in both space and time at that.
This adds a bit of evidence into my post elsewhere on this thread that many humans are indeed fearful of aliens – even ones who seem to be working on their own project very far away and paying us no obvious mind. Interesting.
To answer your question directly, I have been quite excited in a very good way about Tabby’s Star. It doesn’t even have to be due to smart aliens who are really good with tools because even the most conservative astronomers have said it is an unusual celestial phenomenon.
TS is also serving the purpose of getting both the public and professional scientists to look beyond the standard traditional SETI view of aliens who despite being aliens otherwise behave and think like us. This will in turn increase the chances of finding them if for no other reason we push searching via other places and with other methods.
It is not the aliens themselves, that would be unsettling to contemplate, but what is implied by the existence of such aliens.
Sure, once our radio signals reach them, they may decide to throw a few RKVs at us, or a Dyson-Nicoll beam (or something a bit more subtle) just to be on the safe side. But this is so utterly beyond our power to act against (barring some Darwin Award-level ideas like poking them with a laser) that it could as well be a nearby GRB for all we’re concerned.
Whatever they might want with us, if they ever do, is as removed from our level as cosmic phenomena, and in at least three millennia, when our heirs will have access to resources we probably can’t imagine as of now – trying to predict the outcome is a ?/? undetermined.
Unless they are actually building a Dyson-Nicoll projector pointed at what looks like stone age primates that may one day become a problem, but again, if that’s the case there’s absolutely nothing we can do about it, and it would happen too fast for us to understand anyway.
It is actually quite hard to be frightened by something like that.
On the other hand, the implication that they (merely) exist, and how it plays with varied solutions to the Fermi paradox, is something we can relate to, and most answers aren’t looking good.
As always, the only answers to the Fermi paradox that allow us many neighbours and a probability of interstellar travel that isn’t infinitesimal, has to solve that timing issue, such that all ETI forms only started emerging <100 million years ago. There are Ways to answer this that don't impact our future prospects too badly.
Such answers might include that life, AND the Cambrian explosion was seeded from another galaxy, the second only circa 600 million years ago. Another might be that some galactic hazard such as GRB, only diminished sufficiently to allow higher land-based forms 100 million years ago.
@Eth
Interesting pos,t but I have some quibbles.
If Dyson sphere/swarms have any prevalence, then finding one once we actually have sufficient technology isn’t necessarily suspicious. There has to be a first discovery some time. Sometimes we fluke it. Look at gravity waves! Also we weren’t really looking for Dyson spheres with Kepler. The hypothesis got going only when something really weird arose. So I don’t think it’s a case of (say) confirmation bias in a purpose-built Dyson sphere survey.
Even so, if this IS a Dyson sphere, it doesn’t have the IR signature that some expected, (and a basis for previous efforts) thus making detection more difficult. Actually IR seems to be a problem for nearly EVERY idea about Tabby’s Star.
I have seen people argue both for AND against a D.S., based on the lack of IR! With Tabby’s Star, any detection seems like it may be via visible light (so far). So maybe we’re Not Doing It Right, and there are more to be found.
I don’t think the aliens need be related to us as a way of explaining a “coincidence”of finding a Dyson sphere..Some estimates using the Drake Equation give the minimum distance to an ET civilisation as a few thousand light years, so 1500 ly to one at KSC846852 seems to be in the right ballpark for INDEPENDENTLY evolved life. So the odds against it might NOT be “astronomical”. However, “the next one” is liable to be a LOT harder to find owing to the likely distance. Disclaimer: It depends on our assumptions, of course. These discussions always seem a bit circular, including what I say, I guess!
I think their being related to us or not has little bearing on whether they are benign or not.
BTW, none of this means that I’m sure it IS a Dyson Sphere (though I’d like it to be).
Aye to pointing everything we can at it, all the same!
While Kepler didn’t search for Dyson spheres, other studies did, be it in the Milky Way for individual stars, in other galaxies where a fraction of the stars would have Dyson Spheres, or even for galactic Dyson clouds at maximum efficiency (with the galaxy radiating at close to the background radiation temperature). All those concluded that those are mostly absent (or they would have found it), and if they do exist, they are extremely rare.
Now, we haven’t searched for all possible types, and as you point out, if this is really one, we may be wrong about a Dyson sphere signature. Still, they do appear to be rare enough for one right next door to be surprising.
It would also imply that Dyson spheres are short-lived or that (again) technological life just started. Otherwise, there would be so many nearby stars with spheres, we would most certainly have noticed: that we detect the darkening in a timespan of years imply an extremely low construction time, compared to the age of the galaxy, and we can expect to find them in roughly the same fraction of in construction-to-finished than construction time-to-lifespan, if builders have been around for longer than the average sphere lifespan.
So if it takes, let’s be conservative, ten thousand years to build one, but once built they last ten million years, it means that for one sphere in construction, there should be about one thousand completed ones. There are a hundred million stars in the nearest few thousand light years, sure, but given the kind of systematic studies we made, it’s hard to believe we would haven’t detected even one.
As for the Drake equation, either it gives us such distance for independent life at some point of galactic history, but then why would they start building one sphere right now? – or independent life right now, but then where are the many, many previous ones?
Thanks for the reply. Of course what you say about the relationship between construction time, operational lifetime and expected detections makes sense, provided we’re not missing something.
Yes the galaxy studies had apparently negative results.
Maybe (yet) another possibility is something near Tabby’s Star that is intelligently constructed but NOT a Dyson Sphere, which therefore doesn’t emit IR in the way we expect.
Or maybe there’s something about Dyson Spheres that leads to their rapid destruction, so there are few about, but then we’re suspiciously lucky to see one…
Or .. [add numerous ideas including fairies, according to taste :-) ]
Michael.
It should be noted that the kepler-mission did not cover the whole sky. It was only a small fraction in the sky. This results in hundred of other Dyson spheresin we should be able to observe. It is so sad that we spent only the small fraction of money to understand our neighborhood in the galaxy.
It’s too bad Webster Cash’s star shade isn’t ready to help determine if Tabby’s star has a family of planets…The process of elimination has to begin somehow…
Great point. More observational data is only a matter of time.
I have imagined a new hypothesis about this star.
A terrestrial planet has been pushed too near the star beyond roche limit. Because it’s density, it has been fragmented into multiple miniplanets. The aphelion of the orbit its the direction of our Sun. Because the planet has fragmented, in parts, with different orbits, there is not clear pattern by now. The fragments are too big to generate a lot of infrarred like with dust (the orbit in perihelion is too hot and birght for dust to survive). And because we see with the fragments in the aphelion, they are cool.
The Roche limit in general is around 2.4 x the radius of the larger body, or 1.4 radii from the surface. Given the surface temperature of 6750 K, any rocky body would likely vaporize before it could fragment.
Impact fragmentation, however is quite possible, that is how we think our own Moon formed. A Mars-sized body is presumed to have hit the proto-Earth. About 10% ended up in the Moon, and the remainder was absorbed by the Earth or dispersed beyond the Earth-Moon system. A recent giant impact in the KIC 846 system could have created a large debris cloud.
Yet isn’t such an impact ruled-out due to the lack of excess IR from the dust that would be generated by such an impact?
There’s an aspect I don’t quite follow about the crowding stars mistake. If crowding stars occur when a plate is not able to fully resolve them and they overlap, then doesn’t KIC 8462852 have exactly this problem with its apparent companion M dwarf? In images the companion appears as overlapping the primary star and the pair are only separated by Keck adaptive optics. Schaefer says KIC 8462852 doesn’t have the crowding stars problem and so Hippke et al shouldn’t have used an crowding stars as checks. So why does the companion star not count as a crowding star?
I believe that unresolved binaries (which this system is, as far as all of the survey plates are concerned) are not a problem. The problem arises when the two nearby stars are resolved in some but not all plates. The target star in the unresolved images is read as being significantly brighter than the same target star in the resolved images. In the case of the Harvard plates, the post-Gap plates are mostly unresolved, versus many fewer plates in the pre-Gap plates being unresolved. This apparently explains a large proportion of the jumps in magnitude seen in the Hippke et al papers.
Am I missing something? Surely if the M-dwarf was moving in some correlated way with KSC 8462852 (or in a long-period orbit comparable to Proxima Centauri ), then MAYBE it would have been overlapping or nearly so, to varying degrees over decades? IF it’s bright enough, could it have confused magnitude estimates?
I doubt it would make any difference at all, the F type star is a flamethrower and the M type is a firefly.
Yes pretty much what I expected, but thought it was worth considering (I should’ve looked up the data).
I guess that boosts the opinion poll for the aliens slightly, then :-)
I have the same philosophy with this as for elections: I know “who” I’d like to win, but am realistic about how it may turn out when it comes to the test.
Michael T
It’s far from clear that this is the case. It could be a coincidental alignment. In any case, there is no compelling argument that it has anything to do with the anomalous light curve.
Is this M star of any significance, I mean it burns significantly less bright by magnetudes?
Thank you to Bill for the explanation.
The companion M dwarf does seem to be the elephant in the room at the moment. I think getting accurate measurements of its proper motion to see whether it is gravitationally bound to Tabby’s Star or not is going to be really important. If it can be shown to have plowed through Tabby’s Star’s Oort Cloud relatively recently, then it would have undoubtedly perturbed some large Oort Cloud bodies, supporting the comet hypothesis.
A passing M dwarf which had perturbed some large bodies from outer system changing the regular orbits about right at the moment just before Kepler observed the system, the odd is very high of course but not impossible, is this probability higher or lower than the chance of winning the Powerball ~ 1/300,000,000?
If you’re proven wrong about comets, then you’re simply a scientist. If you’re wrong about aliens, then you’re a fool.
“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”
-Sherlock Holmes
DJ Kaplan – If you said angels or Bigfoot, then you might be right regarding fools. But extraterrestrial life in itself is scientifically plausible (so are comets, but giant ones in close herds?). Even the Rare Earthers say there is probably a lot of simple lifeforms throughout the Universe.
Human ideas on alien life, smart and otherwise, are still so parochial and choked by a combination of centuries of social and religious pressure and often really bad science fiction.
Even SETI was founded on some rather biased and limited assumptions. Check out this online book if you want the details:
http://www.daviddarling.info/encyclopedia/S/SETI_critical_history_cover.html
And this:
https://centauri-dreams.org/?p=27889
So while Tabby’s Star may not be host to an alien construction project, at the least it is starting to get folks to think outside the box, including and especially the professionals. They may still cling for now to their decades-old SETI concept of radio signals from distant altruistic aliens living on an Earthlike world around a Sol-type star, but the Universe seldom plays by human wants and needs.
I should add that while there is nothing wrong with Radio SETI and it does have its points, that we are seemingly not being bombarded with alien radio broadcasts means we need to ramp up checking out other methods of interstellar communication. Here are some examples for a refresher:
http://www.coseti.org/lemarch1.htm
LJK, the search space is vast. It’s beyond my own comprehension. It’s like looking for needles in a haystack, and the haystack is the size of North America. We could be swimming in artificial ET signals and not know it. Give it a few decades and we’ll have a better idea but for now it’s not true to say that “we are seemingly not being bombarded with alien radio broadcasts.”
Then let me clarify: We are seemingly not being bombarded by really obvious/strong radio broadcasts.
I think DJ K was speaking from the perspective of peer-professionals in todays competitive climate. If so, then both of you are quite correct.
If you’re proven right about aliens, then of course you’re no fool.
Thank you, Coacervate, I was talking about professional pressure indeed.
Speaking of statistics, it looks as though NASA’s estimates of the sizes and densities of our friends in the meteor belt may have been sadly mistaken.
Allegations include formulas in which diameter and radius have been mixed, and that reflectivity has been calculated inaccurately. (Something that this humanities major might be expected to do.)
I guess accuracy is pretty important when you are looking at bodies that could potentially impact Earth and wipe out a few cities.
The argument of authority is strong in this one. (Yes, he might be right, but the tone irritates the hell out of me.)
My thoughts exactly…( and so many exclamation marks in the PDF)… not saying his analysis is wrong though.
should not anything like a Dyson swarm be ruled out for the same reason planet(s) are ruled out? I mean because the putative absorber is not re-radiating in the Infra red? The missing heat is the real mystery is it not?
If the Megastructure(for me, Dyson Swarm is TOO SPECIFIC a term to be used right now)consists of MIRRORS REFLECTING ALMOST ALL OF THE STARLIGHT before any HEAT can be generated in the “building blocks” themselves, ABSOLUTELY NOT!
You can point your radiators in any direction, with a constructed thermodynamic object. If you want to avoid detection, radiate out of the galactic plane, the number of star systems the radiation cone sweeps out will be minimized.
Maybe, but that’s pretty inefficient. If you can direct it, it’s still free energy. True waste heat is pretty much isotropic.
If there’s missing heat, isn’t one possibility that something is absorbing or converting the heat to something else?
The missing excess IR: I think we make too many possibly naive assumptions, re: expecting to see waste heat it if a mega-structure exists. Try and imagine an ETC technology millions of years more advanced than ours, as Arthur C. Clarke said, indistinguishable from magic to us. The waste heat could be almost completely devoid of energy, a conversion that is close to 100% efficient. And/or it could be direction-ally radiated away, somehow, for some reason. A waste heat beam may only be unintentionally directed at us during a dimming event. And/or it is there, perhaps minuscule amounts of waste heat, but our IR sensitivity is just not up to the task of detecting it, at 1500 ly away.
NOT SO “MAGICAL” AFTER ALL! If you have not already done so, click on the website mentioned in my comment just below(or above?)THIS ONE, read the article, and respond ASAP! Thanks. I would REALLY appreciate your take on this!
Here’s the link to “New Compound can Transform Infrared into Visible Light”:
http://www.sci-news.com/othersciences/chemistry/compound-transform-infrared-visible-light-03940.html
Thanks for the sci-news dot com website, an interesting site in and of itself, now saved as a “favorite”.
I say that any material that can transform IR, or any reflector/mirror, can approach but never attain 100 % efficient. Lets be generous and say it is 99% efficient. That still allows 1 % of 20 % of the entire IR output of Tabby’s Star (20% being the deepest dimming event for Tabby’s) to come shining through as IR. Someone smarter than me should be able to constrain the amount of this IR flux … OR if our telescopes are sensitive enough to detect it from 1500 ly away…. but in my gut it still seems like a LOT of excess IR we should expect being emitted, and probably detectable.
BUT, on the other hand…. re: this new compound and it’s transformed/emitted visible light being “…exceedingly directional….” perhaps the combination of transformation and directionality knocks Tabby’s excess IR down so low it is non-detectable with our current technology.
Maybe JWST. And maybe NOT!
BINGO!!!!! Click on http://www.sci-news.com and read “New compound can transform Infrared into visable light”. It’s mostly made of Tin And Sulfer! I’m still favoring Dirk Bontes’ NATURAL solution, but,should that not stand up to scrutiny, THIS DISCOVERY could swing the argument STRONGLY toward a NON_NATURAL CAUSE!
If anyone wants to read the entire paper, Google Nils Wilhelm Rosemann/Science/new compound.
Thank you for this reference. I have added it as an update to one of my mythology e-books, that already mentioned anti-Stokes fosfor as another substance that converts infra-red light into visible light.
Interviewed Brad Schaefer today. I think I got most listener questions answered. Out soon – tomorrow night at the latest.
http://wowsignalpodcast.com
I think a likely explanation it is that a brown dwarf collided with this star in an angle close to the tangent of rotation. It had large orbital angular momentum, which gave this star a quite large rotation speed, which yielded a large magnetic field. Also, it provided a larger luminosity, which decreases due short, but very frequent coronal ejections. So, these “comets” are actually very large but short lasting star spots.
Can we see your calculations? I understand that the rotation speed is not particularly an outlier for this star, although it is much higher than our sun.
I assume you mean a HEAD-ON collision which COMPLETELY ABSORBS THE BROWN DWARF, leaving NO remanent. The problem with this is that this would produce a “blue straggler” type star whose spectrum will differ SIGNIFIGANTLY from a MAIN SEQUENCE F3 star until it has COMPLETELY radiated ALL the EXCESS ENERGY from the impact. Please review my ABOVE comment regarding a RECENT GRAZING impact with the PUTATIVE companion star which would impart hardly ANY excess heat onto KIC8462852 and thus NOT change its spectrum from a F3V to something else.
I didn’t do any calculation and I don’t know how to do it. I just thought of a magnetic field as generated by moving charges and what would make them move faster without adding significant mass. According to wikipedia, and F type star has 1.0 to 1.4 solar masses and a brown dwarf has up to 8% of a solar mass.
There is a list here of angular momentums: http://www.zipcon.net/~swhite/docs/astronomy/Angular_Momentum.html
So, if the orbital momentum of Jupiter were transferred to the rotational momentum of the sun, its rotation speed would increase by ~4. So, a very excentric brown dwarf, maybe, would increase
No, conclusion not justified (I am assuming you mean -4%?). Please look in the Boyajian 2015 paper, all the best current numbers are there.
Any calculation with magnetic field is extremely complicated – even the best pros find it daunting, but there is no clear causal connection in your speculation. You don’t get a star to dim by even 1% by making it spin at a different rate.
I am not looking for making it dimmer, but a lot brighter. I meant that it is becoming dimmer at a fast rate by loosing angular momentum. The ejected mass is small, but it is fast. It shows up in the luminosity as dips, from lasting large star spots, which lasts a few hours.
To RE-ITERATE: If it DOES become a LOT brighter, THE WHOLE SPECTROM CHANGES and it would NO LONGER BE anF3V star!!! Instead, it would be an ENTIRELY DIFFERENT CLASSIFICATION(i.e. “blue straggler” or blue straggler ANALOG). I do not know the SPECIFIC CLASSIFICATION(can anyone help me out here)but it would DEFINITELY NOT BE F3V, which EVERYONE IN THE ASTRONOMICAL COMMUNITY ACCEPTS AS THE PROPER CLASSIFACATION!
That it is not a blue straggler. I meant a small add of 1% of mass but a lot of angular momentum.
That would be more like a Super-Jupiter than a bonafide Brown Dwarf. If you COULD pull it off with such a low mass, I would be much more amenable to your claim.
There is a link I posted with the angular momentum distribution on the solar system. The Sun has only a small part. Well, with so many stars observed, that could happen in a rather simple way: another planet scatters this brown dwarf/super Jupiter towards the star.
OK, here is LEAST CONTRIVED SCENARIO for the “Deu Ex Machina” arrival of this Super-Jupiter/Very Low Mass Brown Dwarf at JUST THE RIGHT MOMENT to pull your scenario off: The M star “companion” is actually NOT a companion, but was JUST PASSING BY KIC8462852. The S-J/VLMBD was in orbit around the M star, but its trajectory pot it in the path of KIC8462852 in just the way you describe. Th eBEAUTY of this is that it is TESTABLE, and we should know in a relatively short period of time whether this scenario is viable or not.
I am thinking that it is rotating fast, and this by itself, creates a large magnetic field.
And by 4x, i meant angular speed.
I have been asked to comment on this hypothesis.
First of all I do not understand the sentence “it provided a larger luminosity, which decreases due [to] short, but very frequent coronal ejections”.
The hypothetical collission provided a larger luminosity? Just because of the impact only?
And the luminosity decreased and decreases due to coronal ejections? Because these hypothetical coronal ejections block the light from the star?
Look, KIC 8462852 used to be regarded as an unremarkable, rather bland star, until a group of variable star observers noticed something peculiar in its light curve. And even the astronomers and astrophysicists that have studied the star since still regard it as a star and system that is totally unremarkable except for its peculiarities.
There is no indication whatsoever that the star has experienced a collision. If, it had, I would at least expect that its atmosphere has all kinds of trace heavy elements instead of consisting of hydrogen only.
Neither is there any evidence that there used to be a heavy planet or a brown dwarf in the neighborhood. There is just the star and its M type dwarf star companion.
One might as well posit that the phenomena was caused by a purple dragon colliding with the star – a dragon that no one saw before the hypothetical incident, nor during the incident nor after the incident, nor its poop nor its eggs.
Just because a scenario might be possible, does not make it any more likely that it is plausible.
One can easily prove the existence of purple dragons by tweaking known formula’s, but that does not make purple dragons any less non-existent.
Does anyone recall the epicycles that epicycle astronomers loved to teach their students to calculate, taking them weeks to complete their calculation? Do epicycles exist? Epicycles went out of fashion thanks to some lazy students who preferred to rather calculate planetary orbits within a quarter of an hour with the help of one some nifty formula’s provided to them by one Mr. Copernicus.
As I have shown in my astronomy book “Making sense of astronomy & geology” (3rd English edition, 2000;limited edition and out of print) there are plenty of such purple dragons in astronomy.
I also have a lot of stellar collisions in that book (and its earlier editions).
First of all planets (and some of their moons) that collided with their parent star when that changed into a red supergiant of the Mira type variety. Those planets and (one or two) moons changed, in my analysis, into young stars that are now orbiting within their Mira type host star; this is why Mira type variables differ from ordinary red supergiants.
Then my book also – in my analysis – has three neutron stars smashing into something: one colliding with eta Carinae (its parent star used to form a binary with Eta Carina, in my opinion); this neutron star is still orbiting within eta Carinae. Then there is Terebey’s ‘exo-planet’, which in my opinion is a run-away neutron star that grazed one star of the nearby binary star. And as hypothetical third, I am rather convinced that supernova 1987A ejected a neutron star that smashed through a large planet that used to orbit the star.
Then it is rumored that some astrophysical phenomena may be explained by black holes or close binaries merging. (This is explained by tweaking formula’s, so these may be purple dragons. If I see it, I will believe it. But until then it is a purple dragon.)
And then we have the hypothetical – I believe it, though I have as yet not conceived of a mechanism to explain it – collission between a couple of planets that produced the Earth and the Moon (and in my opinion most of the other small planets and moons in our solar system). And of course various kinds of meteorite and comet impacts.
Collissions between stars are exceedingly rare. Whole galaxies can pass through one another without a single star colliding.
I do not believe in purple dragons. There are no arguments supporting the presence of a purple dragon in the KIC 8462852 system.
If I have to choose between purple dragons and a known mechanism that blocks photons – an ionized layer such as known from Cepheid stars – I will prefer the known mechanism every time.
But, what known mechanism is this? And I know these are rare stuff, but, well, this is a rare star we are looking at.
A known mechanism that blocks photons: an ionized layer such as known from Cepheid stars. Simply google Cepheids on wikipedia.
What we need is a theorist.
Why do not ALL stars exhibit behavior like Tabby’s, assuming the cause of the dimming events is an ionized layer blocking light that builds and then dissipates? Because this almost seems as if it is normal for stars to do this and expected….. yet we observe only a single star doing this?
What would trigger this behavior? Is it something unique?
Does it depend on star classification? Size? Density? Mass? Age? Metal content? Rotation rate? Magnetic field strength? Some external (and thus unlikely) cause? (impact, brown dwarf, etc).
Has anyone combed through the Kepler data to look at all the F stars observed? Is there a way to sort through and select only this class? It would be a start, and then possibly expand the analysis up and down the star classes.
Kepler observed about 150,000 stars, and given that F class stars make up about 3% of the population, that is 4500 F stars worth of data to closely look at, seems do-able even for amateurs.
I lost the link to sift through the Kepler data, if anyone can provide it and/or describe how to sort through and select only F class stars, would be much appreciated, thanks!
Daniel and Dirk: Thanks for your combined imput. One way that there would NOT be a photospheric increase in heavy metals is if the Brown Dwarf impactor were EXTREMELY ANCIENT and was composed of ALMOST ENTIRELY HYDROGEN AND HELIUM! If the nearby M star turned out tol be this kind of STAR, it would enhance Daniel’s argument. BUT: I now strongly favor Dirk’s theory as a STAND-ALONE theory, because, for EVERYTHING TO GO RIGHT, the whole scenario would not only have to be contrived, it would have to be CONTRIVED ON STEROIDS! Good luck with trying to get your paper accepted! Maybe then, Schaefer, Hippke, Wright, and Boyajian will be called in as REFEREES! I REALLY WANT A PROFESSIONAL ASTRONOMER’S OPINION ON THIS before I come to a FINAL conclusion.
What I meant by “….the whole scenario…”, I meant the whole IMPACTOR scenario
Both Dirk and Daniel are EXCELLENT theorists! What we REALLY need are EXPERTS FROM THE ASTRONOMY SCIENTIFIC COMMUNITY to REFERREE their theories! I hope this is happening RIGHT NOW with Dirk Bontes'(presumably)submitted paper!
If all F-stars have a thousand year long chaotic transition between internal states of some kind, out of a few billion year lifetime, then if Kepler looked at a few hundred F’s we should consider ourselves lucky that we happened to get one at the right time. If the transition takes a million years, not so much.
Stan, I agree, I think this is what’s going on, some kind of end of life crisis for the star. May have to re-write some astro-physics. To support this hypothesis, what would we predict to see if we are able to grab a spectrum as the star undergoes a dimming event?
I interviewed Brad Schaefer yesterday. He was very upbeat and positive in explaining why he is sticking to his guns r.e. the century long dimming and provided a bit more depth on the Kepler data analysis Ben Montet has been doing. He provided enthusiastic support for the Boyajian kickstarter campaign to buy telescope time to monitor the star (which no doubt everyone on here has contributed to):
http://www.wowsignalpodcast.com/2016/05/season-3-episode-6-not-glimmer-of-idea.html
Paul, thanks for another excellent podcast interview, and now I have jumped the fence and am back on Brad’s side! Back and forth we go, we desperately need more data, especially spectral data during a dimming event. However it resolves itself, it will be interesting.
I can’t shake this thought so please indulge me (and excuse if this has already been floated).
In a matter-dominated universe, anti-matter is scarce and valuable. A few years ago CERN announced proudly that they had held anti-matter for some 15+ minutes. They are getting better at “handling” the stuff all the time.
I makes me wonder if the missing light from KIC8462852 is being converted according to M=E/c^2 into anti-matter as a form of fuel. If their process was sufficiently efficient to keep the heat loss to a minimum it seems (to me) to explain the data at least as well as Tabby’s massive swarm of comets.
I think that a star’s worth supply would be desirable to anyone wishing to approach light-speed with payloads more than a few grams, or stabilise a worm hole and so on?
So you are not just positing a super-efficient machine (no IR emissions), but speculating that it is making anti-matter. Tou might as well suggest that they are space yards, or better yet, gigantic sails of star ships blocking the light of Tabby’s star. ;)
Rather than speculating with very limited data, we need to step back and gather more and different observations. If the star is dimming as well, is this real, and if so, is it unique, or are there more stars with such behaviors, and if so, why?
Remember when Greg Benford suggested stars might be alive? Perhaps this is the star getting ready to propel itself? (I don’t believe that for a second, but I raise it because speculation can lead us into all sorts of wild fantasies without solid evidence).
Alex, I believe it was Dr Greg Matloff that put forward the idea of stellar conciousness not Dr Greg Benford.
“I makes me wonder if the missing light from KIC8462852 is being converted according to M=E/c^2 into anti-matter…”
Einstein’s equation shows a classical equivalence not a mechanism. There are mechanisms that involve QM and that result in unique spectra depending on the particles involved. These can and have been astronomically observed. However not in this instance that I’ve seen.
I solved the mystery. It are completely ionized helium (or hydrogen) atoms that are preventing some of its light from escaping from the star. It is similar to what happens in Cepheids. https://goo.gl/ng7ey9
Dirk:
Although I like your hypothesis, it would be better served if you could defend it in this forum.
EricSECT: Mr Bontes apparently REFUSES TO DO SO! Please start at the TOP of ALL OF THESE COMMENTS, then SCROLL DOWN to LasloM’ s May 26,2016 comment regarding Mr Bontes’ theory(which, up until then, I TENDED to believe). READ IT IN IT’S ENTIRETY! Then please note my comment DIRECTLY BELOW HIS! It’s been almost two weeks, and…NOTHING! LasloM’ refutation was VERY Schaeferian in its tone For ME to START believing again, I would need to sew Mr Bontes POINT FOR POINT rebuttal of LasloM’s refutation!
Sorry, I missed that message from two weeks ago. I have been busy with other things. Later today or tomorrow I will give this thread my attention.
Dirk:
We all look forward to your response. If your hypothesis is correct, it could be revolutionary. If you don’t act and the idea has merit, someone else will grab the ball and run with it.
Boyajian and Wright answered many questions recently on http://www.cosmosup.com. regarding the LATEST on KIC8462852. Nothing EARTH-SHATTERING here, but everyone should check it out anyway.
Um, it will take me some time to read all the responses on this thread. I hope to do so this evening and to respond tomorrow.
I’m suddenly seeing a wave of UFO comments being submitted to this thread, none of which I will publish. For those coming here for the first time, let me quote from the Administrative page, where the comments policy is found:
——-
… please note that UFOs are not a topic I deal with on Centauri Dreams. This is not out of lack of interest in the possibilities but because of two facts:
1) There are many sites on the Internet that specialize in the subject, so I leave it to them, and:
2) Past experience has shown that when the discussion turns to UFOs, it quickly evolves — no matter what the original topic was — into arguments over the existence of UFOs, arguments that are all too often counterproductive and take us far off topic.
Centauri Dreams is not about the existence of UFOs, nor about alien abductions, ‘ancient astronauts’ or other New Age talking points. I have no idea what UFOs are. Because the evidence is anecdotal and non-reproducible, the Tau Zero Foundation chooses to leave their study to others. I note with approval what Tau Zero Foundation director and founding architect Marc Millis has to say:
“Tau Zero does not study UFOs. The topic is too mired in anecdotal, perception-based evidence rather than on irrefutable physical evidence. Additionally, a fair and impartial study would have to include a significant investigation into psychology and sociology. Such excursions are beyond the scope of Tau Zero.”
And also beyond the scope of Centauri Dreams.
Any chance its a Uranus style planet (axis parallel to plane of revolution around the star) with a large disc / ring structure around it (covering ~20% of the star’s projected area max) with intermittent spaces in the disc but is also wobbling like a top? (this could explain the asymmetric dimming). Not sure how to explain this without a picture and not sure how to attach a picture here.
Nope, too small. Rings need to be close to or inside the Roche limit, and anyway, rings can’t explain the D800 dip at all. The kind of rapid precession you describe has no physical mechanism.
Fair point on D800.
On the rings and Roche limit, I assumed that the phenomenon was akin to Saturn or Phoebe where the ring lies outside the Roche limit. And assumed a planet 1.5x Jupiters radius with density of Saturn for the planet and ice density for the ring. This cam come pretty close to ~40% of the stars radius
But fair point that it wont explain anything
I have not yet written a science paper. I am struggling with another deadline. Too, the astronomy institute I asked for support in writing a science paper is playing dead and not responding.
Dirk,
What would your hypothesis predict as to the polarization of the stars light before/during/after a dimming event?
I spent from 1990 until 1995 writing a cosmology book, never published except for one chapter about the darkness of the sky on a blog page (I published that when someone else had the same idea and published it before I did).
I do recall that I discussed polarization of light in that book, but I do not recall the specifics nor whether I solved the particular problem I discussed. I do recall that my stumbling block was the polarized condition of reflected light (from say a window pane); I quit writing the book when I could not explain that. As well as having other subjects to occupy my attentiona and mind.
The index of my astronomy book, that has the ideas on which my article about KIC 8462852 is based, does not contain a lemma for ‘light’. It does have a couple of lemma’s for ‘polarization’, but those refer to magnetic field lines. It also has a quote of several paragraphs about the polarization of light emitted by stars, from “Introductory astronomy & astrophysics” (1987, pp. 340, 372-373) by Michale Zeilik & Elske v. P. Smith).
So my guess is that I do not expect to see any change in the polarization of its light during the dimming event.
A pragmatic use of energy available to an ET civilization, or ours, might be to signal over a lengthy period of time (centuries) rather than a condensed signal bundle. Using this transform effect, signal peaks would have significance of place rather than amplitude.
Mark your calendar: Gaia data release set for 14 September
http://sci.esa.int/gaia/58042-mark-your-calendar-gaia-data-release-set-for-14-september/
Since KIC 8462852 is in the Tycho catalog: TYC 3162-665-1
We should be able to compare the apparent magnitudes from Hipparcos and
Gaia catalog and see if there has been any dimming since the early 1990s.
Very nice !
We could see new day-long dimming with this data ? Or ony for the century-long dimming ?
How good is the photometry on these two missionsm
Hipparcos the median photometric precision was 0.0015 mag with
110 observations per star.
I didn’t see a similar figure for Gaia, I emailed the folks that
Run Gaia so that we can compare the two spacecrafts accuracy.
Fortunately many of the same people worked with both telescopes.
Dave
According to Table 2 in this paper describing the Tyco-2 catalog: http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2000A%26A…355L..27H&db_key=AST&nosetcookie=1
The standard photometric error for Tabby’s Star would be 0.114 in V and 0.173 in B. It’s much smaller for the brighter stars in the TYC. TYC lists magnitudes for this star much dimmer than APASS:
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=KIC+8462852&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id
Paul, Those figures look like single observations
Not the 110 averaged in the catalog.
Dave
Well, I could be wrong in my interpretation, but I think Table 2 applies to the catalog entries, not individual observations: http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-info=XML&-out.add=.&-source=I/259/tyc2&recno=781574
Can you cite a reference for 110 observations? I can’t find it in the Tycho 2 catalog, but I am accessing it through Vizier.
http://sci.esa.int/hipparcos/47357-fact-sheet/
Main Experiment
Number of stars 100 000
Limiting magnitude V = 12.4 mag
Complete to V = 7.3 – 9.0 mag (*)
Positional accuracy 0.002 arcsec (B=9 mag)
Parallax accuracy 0.002 arcsec (B=9 mag)
Proper motion accuracy 0.002 arcsec per year (B=9 mag)
Systematic errors 400 000
Limiting magnitude B = 10 – 11 mag
Positional accuracy 0.03 arcsec (B=10 mag)
Photometric accuracy 0.05 mag in B and V (per observation)
Observation per star approx. 100
*depending on galactic latitude and spectral type
http://www.cosmos.esa.int/web/gaia/science-performance#photometric%20performance
Below are details on Gaia’s photometric performance, I contacted the Gaia help desk and requested a define in the same terms used for Hipparcos if possible. Gaia has 70 observations listed for a 5 year mission, the spacecraft has enough consumables for an additional year after the primary mission.
2. Photometric performance
Gaia’s photometry comprises:
broad-band white-light G-band fluxes obtained in the astrometric instrument, and
low-resolution spectro-photometry obtained in the Blue and Red Photometers (BP and RP).
The wavelength coverage of the astrometric instrument, defining the white-light G band, is ~330-1050 nm. The Sloan/Cousins/Johnson magnitude/colour transformations presented in 2010A&A…523A..48J allow estimation of the broad-band Gaia G magnitude as a function of V and V-IC valid over a wide colour interval. For ease of reference, we repeat from 2010A&A…523A..48J the relation to convert Johnson V and Johnson-Cousins V-IC to Gaia G:
G = V – 0.0257 – 0.0924 · (V-IC) – 0.1623 · (V-IC)2 + 0.0090 · (V-IC)3,
where the fit error is 0.05 mag. For relations using V-RC, RC-IC, or B-V or for relations linking Sloan magnitudes (g or r) and colours (g-r, g-i, or r-i) to Gaia G magnitudes, please see 2010A&A…523A..48J.
The spectral dispersion of the photometric instrument is a function of wavelength and varies in BP from ~3 to ~27 nm pixel-1 covering the wavelength range ~330-680 nm. In RP, the wavelength range is ~640-1050 nm with a spectral dispersion of ~7 to ~15 nm pixel-1. The 76%-energy width of the line-spread function along the dispersion direction varies along the BP spectrum from 1.3 pixels at 330 nm to 1.9 pixels at 680 nm and along the RP spectrum from 3.5 pixels at 640 nm to 4.1 pixels at 1050 nm. Whereas the G-band data are particularly useful for stellar variability studies, the BP/RP spectra allow the derivation of astrophysical parameters, such as interstellar extinctions, surface gravities, etc., needed for the scientific exploitation of the astrometric data. Over the five-year mission lifetime, a star transits the photometric instrument on average ~70 times, leading to ~70 transits in BP and ~70 transits in RP (the dependence on ecliptic latitude is summarised in this table).
The photometric standard errors of the integrated G-band, BP-band, and RP-band are calculated following the recipe outlined in GAIA-JDB-022. The standard-error calculation includes all known instrumental effects, including straylight as measured during the in-orbit commissioning phase (July 2014). These figures show the single-field-of-view-transit photometric standard errors as function of G magnitude and V-IC colour index (see 2010A&A…523A..48J). The figures refer to median straylight conditions over a spacecraft rotation period and have 20% margin for the BP and RP bands included. As for astrometry, the bright-star errors – which depend sensitively on the TDI-gate scheme as well as on magnitude – have been set to a constant noise floor. A simple performance model which reproduces the single-field-of-view-transit G-band photometric standard errors displayed in these median-straylight figures is:
?G [mag] = 10-3 ? (0.04895 ? z2 + 1.8633 ? z + 0.0001985)1/2,
where z = MAX[100.4 ? (12 – 15), 100.4 ? (G – 15)]. This parametrisation for the G band does not carry margin.
For the BP/RP photometers, there is a V-IC dependence, as follows:
?BP/RP [mag] = 10-3 ? (10aBP/RP ? z2 + 10bBP/RP ? z + 10cBP/RP)1/2,
where z = MAX[100.4 ? (11 – 15), 100.4 ? (G – 15)], and
aBP = -0.000562 · (V-IC)3 + 0.044390 · (V-IC)2 + 0.355123 · (V-IC) + 1.043270;
bBP = -0.000400 · (V-IC)3 + 0.018878 · (V-IC)2 + 0.195768 · (V-IC) + 1.465592;
cBP = +0.000262 · (V-IC)3 + 0.060769 · (V-IC)2 – 0.205807 · (V-IC) – 1.866968;
aRP = -0.007597 · (V-IC)3 + 0.114126 · (V-IC)2 – 0.636628 · (V-IC) + 1.615927;
bRP = -0.003803 · (V-IC)3 + 0.057112 · (V-IC)2 – 0.318499 · (V-IC) + 1.783906;
cRP = -0.001923 · (V-IC)3 + 0.027352 · (V-IC)2 – 0.091569 · (V-IC) – 3.042268.
These parametrisations for BP and RP do have 20% margin included.
Sky-average end-of-mission median-straylight photometric errors can be estimated by division of the single-field-of-view-transit photometric standard errors by the square root of the number of observations (~70 on average). With an assumed calibration error of 30 milli-magnitude at CCD level, the following end-of-mission median-straylight photometric errors, in units of milli-magnitude, would be reached (including 20% margin for G, BP, and RP):
B1V G2V M6V
G [mag] G BP RP G BP RP G BP RP
3 – 13 1.4 4 4 1.4 4 4 1.4 4 4
14 1.4 4 4 1.4 4 4 1.4 5 4
15 1.4 4 5 1.4 4 4 1.4 6 4
16 1.5 5 5 1.5 5 5 1.5 11 4
17 1.5 5 8 1.5 6 6 1.5 26 5
18 1.7 8 16 1.7 10 9 1.7 63 6
19 2.3 16 37 2.3 23 20 2.3 158 9
20 4.0 37 91 4.0 56 48 4.0 395 20
Due to the time-variable straylight levels that Gaia experiences over a spin period and hence over the mission, the photometric standard errors of a given source will not be homoscedastic but heteroscedastic. If, for particular investigations such as variability studies, photometric standard errors for other than median straylight levels are needed, click here.
The Gaia spectro-photometric data from the blue and red photometers (BP and RP), sometimes in combination with the astrometric and the RVS spectroscopic data, allow to classify objects and to estimate their astrophysical parameters. A detailed overview of these efforts is given in 2013A&A…559A..74B. The accuracy of the estimation of the astrophysical parameters depends on the G magnitude and on the value of the stellar parameters themselves. Early investigations have been reported in 2012MNRAS.426.2463L. The most recent investigations show that, for FGKM stars at G = 15 mag with less than two magnitudes extinction, effective temperature Teff can be estimated to within 1-2% (~75 K), surface gravity log(g) to 0.2 dex, and metallicity [Fe/H] to 0.1 dex, using just the BP/RP spectro-photometry. Performance degrades at larger extinctions, but not always by a large amount. Extinction can be estimated to an accuracy of 0.06 mag for all stars at G = 15 mag across the full parameter range with a priori unknown extinction between 0 and 10 mag. The above-quoted performances are somewhat optimistic for two reasons: (1) they are based on pre-launch, no-straylight simulations, and (2) they refer to internal errors, i.e., they assume no significant mismatch between synthetic and real spectra and careful calibration. Without any such calibration, an estimate of the external errors for FGKM stars at G = 15 mag is about 250 K for Teff, 0.15 mag for extinction, 0.5 dex for log(g), and 0.3 dex for [Fe/H]. Furthermore, the strong and ubiquitous degeneracy in effective temperature and extinction (e.g., 2011MNRAS.411..435B) will limit the accuracy with which either parameter can be estimated at the faintest magnitudes.
http://www.rssd.esa.int/SA-general/Projects/Hipparcos/CATALOGUE_VOL1/sect1_03.pdf
Ok The Hipparcos Wiki Entry says 110 observations without a reference, Here is a reference that says 110 observations.
The resulting collection of epoch photometry comprises a total of 13 000 000 obser-
vations, an average of some 110 observations for each of the 118 000 programme
stars. While significant variations in the number of observations occurred, primarily
related to the object’s ecliptic latitude, the Hipparcos Epoch Photometry represents
the largest compilation of high-precision, multi-epoch photometry acquired to date. It
consequently defines a uniform all-sky photometric system, unaffected by seasonal and
hemisphere-related influences.
I looked hard for the Epoch photometry for Tabby’s Star, which is TYC-3162-665-1, and no joy. The Epoch photometry is at : ftp://cdsarc.u-strasbg.fr/pub/cats/I/239/epophot/
It is sorted by the first two TYC numbers, so it would be in in the folder ‘tep31’, but according to the index file it’s not there.
Tabby’s Star also seems to be missing from the Hipparcos main catalog, which only catalogs 118,000 objects, all of which appear to be brighter. It is in the Tyco 2 catalog, so I think the estimates of photometric error listed there are probably the best we’re going to get.
Below are my results with VizieR Modified Query TYC 3162-665-1
(arcmin 1) :
http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ578ae4159bd8&-out.add=.&-source=I/259/tyc2&recno=781574
VTmag 12.103 mag [1.905,15.193] Tycho-2 VT magnitude (Note 7) (phot.mag;em.opt.V)
e_VTmag 0.200 mag [0.009,1.468] s.e. of VT (Note 7) (stat.error)
Note (7) : Blank when no magnitude is available. Either BTmag or VTmag is always given. Approximate Johnson photometry may be obtained as:
V = VT -0.090*(BT-VT)
B-V = 0.850*(BT-VT) Consult Sect 1.3 of Vol 1 of “The Hipparcos and Tycho Catalogues”, ESA SP-1200, 1997, for details.
https://en.wikipedia.org/wiki/Tycho-2_Catalogue
The Tycho-2 positions and magnitudes are based on the observations collected by the star mapper of the European Space Agency’s Hipparcos satellite. They are the same observations used to compile the Tycho-1 Catalogue (ESA SP-1200, 1997). However, Tycho-2 is much larger and a bit more precise, because a more advanced reduction technique was used.
The U.S. Naval Observatory (USNO) first compiled the ACT (Astrographic Catalog/Tycho) Reference Catalog, containing nearly one million stars, by combining the Astrographic Catalogue (AC 2000) with the Tycho-1 Catalogue; the large epoch span between the two catalogs improved the accuracy of proper motions by about an order of magnitude. Tycho-2 now supersedes the ACT.
Proper motions precise to about 2.5 milliarcseconds per year are given as derived from a comparison with the Astrographic Catalogue (AC 2000) and 143 other ground-based astrometric catalogues, all reduced to the Hipparcos celestial coordinate system. There were only about 100,000 stars for which proper motion could not be derived. For stars brighter than Vt=9, the astrometric error is 7 milliarcseconds. The overall error for all stars is 60 milliarcseconds. The observational period was from 1989.85 to 1993.21 and the mean satellite observation epoch is 1991.5.
Photometric accuracy for stars brighter than Vt=9 is 0.013 magnitude; for all stars it is 0.10 magnitude.
The good folks at the Gaia Help Desk replied. I will have to wait for the second Gaia Release which will have integrated blue and red photometric which can be compared with the Hipparcos photometric data. The second Gaia release is scheduled for the 4th quarter of 2017.
Dave