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Unmanned Spaceflight.com _ Telescopic Observations _ KIC 8462852 Observations

Posted by: JRehling Oct 15 2015, 04:45 PM

Kepler found one very, very strange case:

http://www.theatlantic.com/science/archive/2015/10/the-most-interesting-star-in-our-galaxy/410023/

In a nutshell, while Kepler was observing it, the star (larger and brighter than the Sun) exhibited four dimming events that took place at irregular intervals, blocked a lot more light than a Jupiter-sized planet would block, and had a "shape" that varied in all four cases and did not resemble a planet.

This case is attracting some wild speculation… in fact, it is seemingly certain that something wild must be going on; it's just a matter of which wild scenario is the correct one.

If I had to throw my hat in the ring, I'd guess that a distant collision and breakup has placed big swarms of matter into a very long-period orbit. But there's no hypothesis that's been offered that doesn't seem problematic.

Posted by: ZLD Oct 15 2015, 08:42 PM

Yeah, I will be patiently waiting and excited if the hypothesis in the article holds true but I would put all my cards into a strange and rather rare occurrence with the possible passage of a large mass body passing too near the larger system, causing large disruptions. Such an instance could have tons of possible outcomes. Its certainly an interesting event to follow regardless!

Posted by: scalbers Oct 15 2015, 10:08 PM

Could this be like some of the dense clouds that eclipse Epsilon Aurigae on occasion?

Posted by: ngunn Oct 15 2015, 10:09 PM

Kepler is designed to look for transits - but how do they deduce transits from this observation? For me a diagnostic property of transits is regularity. I presume they don't have any system geometry to go on but only an odd-looking light curve. Star behaving badly is what I would call it.

Posted by: JRehling Oct 15 2015, 10:29 PM

The research paper says that the properties of the light curve "strongly rules out" the sort of variable star that is known to exist for a star of this size and color. In a nutshell, it changed far more rapidly than the known cases of such variables. Also interesting (to me), one of the dimming events had a spiky and symmetrical shape.

Of course, it's a given that whatever is going on is very weird, so by definition, it doesn't match any known cases of anything.

The paper, including their discussion of the possibility that this is just a variable star is here:

http://arxiv.org/pdf/1509.03622v1.pdf

Posted by: ZLD Oct 16 2015, 12:26 AM

I think the biggest peculiarity that rules out a lot of things is how short the period is at .88 days. They're findings concluded that it probably wasn't starspots, but I can't help but to think it could be something really strange like that as well.

Posted by: JRehling Oct 16 2015, 04:27 AM

QUOTE (ZLD @ Oct 15 2015, 05:26 PM) *
I think the biggest peculiarity that rules out a lot of things is how short the period is at .88 days. They're findings concluded that it probably wasn't starspots, but I can't help but to think it could be something really strange like that as well.


The strange phenomenon doesn't have a period of 0.88 days; the star's rotation has a period of 0.88 days. The strange, aperiodic dimming happens on a much slower timescale. There were over 700 days between the first two occurrences, then about 20 days separating the second to third and third to fourth occurrences, which each last several days. This is part of what makes it seem very unlikely that the phenomenon is occurring only within the star itself.

Posted by: nprev Oct 16 2015, 04:44 AM

What spectral class is this star? Higher rotation speeds seem to be associated with brighter, more massive, and generally more youthful stars.

If it's both young and luminous, this fast rotation may mean that considerable amounts of material are being shed from the star. Perhaps what we're seeing are massive CMEs interacting with circumstellar gas and dust...?

Posted by: ZLD Oct 16 2015, 05:28 AM

@JReling: Thanks for the correction. I skimmed it earlier and thought I understood differently.

Posted by: silylene Oct 16 2015, 02:43 PM

We need to account for a few facts here (see the paper for many more):

Eclipses at least 22% obscuration of the KIC 8462852 star
There are multiple large eclipsing objects, and each object must have orbital periods at least several years (because no periodicity was noted within the observational span, which means none of them repeated exactly, at least none repeated with the same obscuration).
Some of the large objects look 'grouped' in their obscuration, in the sense that the eclipses occurred in very close time proximity.
There is also a small object which orbits with a 20d period.
There is a 0.88d cycle is likely a starspot, which assume the star revolves around its axis a fast 0.88d.
Infrared data doesn't support collisions or even comets.

My speculation which doesn't involve alien constructs or other woo hypotheses:

The star has several exoplanets which orbit it at various distances with periods of many years, so each exoplanet may have only been observed once in the data set.
Some of the exoplanets are ringed systems with very opaque rings tilted out of the ecliptic with no noticeable ring gaps. The exoplanet at 793d with the 22% obscuration has a HUGE dense ring system that is inclined such that it can eclipse 22% of the star's illumination as see from earth.
Some of the exoplanets have very large exomoons orbiting them. (this accounts for the secondary obscurations observed in close time proximity to the major obscurations, for example in the data between 1500-1600 days).
Maybe the large exoplanet at 793d and 1520d is the same exoplanet, just the ring angle changed, and at 1519d an exomoon was observed with it.

Posted by: JRehling Oct 16 2015, 04:10 PM

QUOTE (nprev @ Oct 15 2015, 09:44 PM) *
What spectral class is this star? Higher rotation speeds seem to be associated with brighter, more massive, and generally more youthful stars.

If it's both young and luminous, this fast rotation may mean that considerable amounts of material are being shed from the star. Perhaps what we're seeing are massive CMEs interacting with circumstellar gas and dust...?


It's an F3, larger and brighter than the Sun, similar to Procyon. It doesn't show the IR brightness that would imply a large dust disc, which seems to eliminate one of the possible explanations.

I've wondered about a highly elliptical orbit for the "junk" that's causing the dimming. If it's on a long period orbit, then it might remain cool because it spends very little time near the star. That is essentially the spirit of the authors' explanation, a massive swarm of long-period comets. I wonder if the debris from a collision, now in a long-period orbit, might not be able to produce the same result.

Posted by: JRehling Oct 16 2015, 04:27 PM

QUOTE (silylene @ Oct 16 2015, 07:43 AM) *
My speculation which doesn't involve alien constructs or other woo hypotheses:
[...]
Some of the exoplanets are ringed systems with very opaque rings tilted out of the ecliptic with no noticeable ring gaps.


The third event, at 1541 days, is very intriguingly symmetrical: It has three peaks, with the two outer ones being approximately equal in depth and distance from the larger, central one. That makes me wonder about a ringed planet.

But the other three events don't show that pattern. Event #1 is single-peaked and quite smooth, while Event #4 is double-peaked. Event #2 is pretty messy: It has three peaks, but no symmetry.

So I wonder if Event #3 is due to a ringed planet with the planet and rings participating, and Event #4 due to a ringed planet with only the apsa of the rings participating, and the planet "missing" the star during the event.

Keep in mind that for something opaque to cause a dip of 22%, for a star with 1.58 times the radius of the Sun, the cross sectional area of the transiting object has to be at least 55% the cross section of the Sun, or about 55 Jupiters' worth of cross section. This is a big object or set of objects! A planet + ring system would have to have at least 4 times the diameter of Saturn's rings to accomplish this, like rings extending from Jupiter's cloud tops out to Europa or from Saturn's cloud tops out to Rhea.

And that scenario with rings that we see face-on from Earth would be provided only if the rings were perpendicular to the planet's orbit, which is unlikely to occur by chance; any deviation from that geometry would require a still larger ring system to provide the observed darkening.

That might just work if we only had one such event to explain, but four of them means that there would be at least three different giant planets with three gigantic ring systems. I can't see how that would happen.

Posted by: HSchirmer Oct 17 2015, 12:41 PM

QUOTE (JRehling @ Oct 16 2015, 05:27 PM) *
...
Keep in mind that for something opaque to cause a dip of 22%, for a star with 1.58 times the radius of the Sun, the cross sectional area of the transiting object has to be at least 55% the cross section of the Sun, or about 55 Jupiters' worth of cross section. This is a big object or set of objects! A planet + ring system would have to have at least 4 times the diameter of Saturn's rings to accomplish this, like rings extending from Jupiter's cloud tops out to Europa or from Saturn's cloud tops out to Rhea.
...
That might just work if we only had one such event to explain, but four of them means that there would be at least three different giant planets with three gigantic ring systems. I can't see how that would happen.


Eh, guess we might be seeing the system during a late heavy bombardment / nice-model period of orbital chaos?
Hmm, two hot jupiters swapping places, each dragging along debris fields of trojans. In the nice model, is there a scenario where Jupiter and Saturn don't scatter, but merge, or end up a close binary; basically something huge and gaseous and opaque, that might be {relatively} cool, at least in contrast to simply smashing two earth sized planets together?

Thinking about outside effects, what happens if a brown dwarf binary, e.g. Luhman 16, drifts into the system?

Posted by: scalbers Oct 17 2015, 01:17 PM

Here's a web page that helps explain Epsilon Aurigae that might have some parallels as suggested earlier:

http://www.daviddarling.info/encyclopedia/E/Epsilon_Aurigae.html

Posted by: ngunn Oct 17 2015, 08:54 PM

Accepting the idea of eclipsing objects of some kind, why do they have to be in orbit around the star? Couldn't they be anywhere in the line of sight? So far there is no evidence of periodicity that would arise from regular orbits, only a sequence of apparently one-off events. If the objects are in a much closer but very faint system that just happens to be aligned with the star then they wouldn't have to be so big to produce the observed degree of obscuration - and of course they'd only pass once.

Posted by: HSchirmer Oct 18 2015, 12:07 PM

QUOTE (ngunn @ Oct 17 2015, 08:54 PM) *
Accepting the idea of eclipsing objects of some kind, why do they have to be in orbit around the star?
Couldn't they be anywhere in the line of sight?


I was thinking that same thing, perhaps we're seeing something closer?

This WTF star is estimated to be around 1480 LY from earth, in the Cygnus constellation.
It's just up and right from a star cluster NGC 6866 (arrow below)


First, that's looking towards the galactic center, the densest area for stars, and molecular clouds and other dark stuff, e.g. steppenwolf planets and brown dwarfs. So, perhaps it's a transit by something closer, a brown dwarf with planet(s) or a brown dwarf with comet belts.

Second, turns out that there is a nearby (~14 LY) triple star system https://en.wikipedia.org/wiki/G_208-44/208-45 in the same area as WTF (1450 LY).
So, let's assume the triple system has ejected something, planets or shredded comets. They would be 100 times closer, and thus could be 100 times smaller to cause the occultation. Instead of hypothetical object(s) ~50 Jupiter diameters across, object(s) 1/2 the diameter of Jupiter ( a normal ice-giant planet) could be the explanation.

Posted by: JRehling Oct 19 2015, 08:12 PM

Interesting thoughts, nprev and HSchirmer. The first thing to grapple with is the probability of an object in one system transiting a coincidentally-aligned more distant star. The next thing to grapple with is the probability of four such events happening in a short time. In addition, the shapes of the events are still weird. And, finally, in such a paradigm, it becomes a little odd that no such event completely eclipsed the distant star, reducing its observed brightness to zero.

The last two might be addressed if we imagine that these are comet-like. Then, in fact, the star may be getting completely covered in terms of area, but by a translucent object. And the first objection may be addressed by a "Birthday Theorem" of sorts: Given enough object pairs, some really precise alignments may occur.

It's the second objection that seems thorniest: How can the closer system have so many objects that transit the more distant star? It would require either that the closer system have a dense halo of large objects or that the closer system has a lot of large objects orbiting in the same plane that coincidentally contains the farther star.

I don't know. Something weird is happening. The closer-and-farther system case seems to handle one weird aspect of the data – the size of the objects – but adds another weird thing – the coincidental perfect alignment – and maintains several of the weird things from the single-system hypothesis. I don't know which, if either, of those two explanations is more likely.

Posted by: ngunn Oct 19 2015, 09:19 PM

QUOTE (JRehling @ Oct 19 2015, 09:12 PM) *
It's the second objection that seems thorniest: How can the closer system have so many objects that transit the more distant star? It would require either that the closer system have a dense halo of large objects or that the closer system has a lot of large objects orbiting in the same plane that coincidentally contains the farther star.


I've been thinking about this too. To observe eclipses in a single system you need one coincidence: The plane of the system must be aligned with us. For a nearer system to produce multiple eclipses of a more distant star you need two coincidences. The nearer sustem must be edge on to us as in the ordinary case, but in addition its proper motion relative to the background star must be in the same direction also to carry the whole succession of objects across the star from our viewpoint. If the nearer system is fairly compact, almost like Galilean moons around a brown dwarf for example, that may not be too much to ask. I agree with you it's difficult to call the relative improbability of this versus a single system scenario. It's clearly something improbable or we would be seeing more of them! For the moment, though, I'm noticing a sequence of events that happens only once and a degree of obscuration that suggests to me that the eclipsing objects are much closer than the star.

Posted by: HSchirmer Oct 19 2015, 09:26 PM

QUOTE (JRehling @ Oct 19 2015, 09:12 PM) *
I don't know. Something weird is happening.
The closer-and-farther system case seems to handle one weird aspect of the data – the size of the objects – but adds another weird thing – the coincidental perfect alignment – and maintains several of the weird things from the single-system hypothesis.
I don't know which, if either, of those two explanations is more likely.


Basically, I'm following an old saying "if you see hoof prints, think horses, not unicorns"
Better to go with something known-but-extremely-unlikely rather than something entirely-unprecedented.

Basically, it's a "devil you know" situation- which is more unlikely? What is the least bizarre explanation?

A - A nearby star with multiple opaque objects in a tight orbital plane, that all happen to occult a distant star?
B - A distant star with multiple opaque objects in a tight plane, that all happen to be several Jupiters across?

So, how certain are we about the WTF star? IRC, the classification is F-type, 6k-7k kelvin, located about 1,400 LY away.
Ok, what if it's not a "normal" distant F star, but a variant of procyon, (F star and white dwarf) but with a white dwarf that has a 6k-7k temperature. So, what would a near by white dwarf pulling material from a brown dwarf look like? Could it be something with the temperature and H2 lines that resemble a F class star? The luminous star would be roughly earth sized, and thus the observed occultations could be a result of "standard" rocky planets or dwarf planets.

Posted by: Hungry4info Oct 20 2015, 12:48 AM

Look at the light curve. A dark sphere transiting a luminous sphere doesn't fit the data well.

Posted by: JRehling Oct 20 2015, 02:09 AM

Comet Hale-Bopp's tail had a maximum length of over 60 million km. Comets can easily exceed Jupiter in size, and then some. However, one comet like Hale-Bopp wouldn't obscure a star; the tail is translucent. So this phenomenon couldn't be explained by one Hale-Bopp. But if a larger body, or set of bodies traveling together, were outgassing as much as Hale-Bopp did, we might have an explanation for this which isn't too crazy.

Posted by: JRehling Oct 20 2015, 05:46 PM

Another thought: A comet seen transiting its star would be, most likely, pointing its tail directly away from the star and directly towards us. This would reduce its size, but increase its opacity. We have never observed a comet in this solar system from that geometry.

From Keplerian considerations, the transiting objects, if orbiting KIC 8462852, is more than 3 AU distant. Because this star is much brighter than the Sun, that may correspond to high levels of cometary outgassing.

Posted by: HSchirmer Oct 20 2015, 06:50 PM

QUOTE (JRehling @ Oct 20 2015, 06:46 PM) *
Another thought: A comet seen transiting its star would be, most likely, pointing its tail directly away from the star and directly towards us. This would reduce its size, but increase its opacity. We have never observed a comet in this solar system from that geometry.

From Keplerian considerations, the transiting objects, if orbiting KIC 8462852, is more than 3 AU distant. Because this star is much brighter than the Sun, that may correspond to high levels of cometary outgassing.


Well, comets can have multiple dust tails, and a separate ion tail. Not sure if the ion tail eventually coalesces back to normal material at some great distance.

Shoemaker Levy's beads-on-a-string appearance comes to mind.

Posted by: Rittmann Oct 20 2015, 08:49 PM

I was wondering...

How much obscuring could happen in a system like ours of some big body with plenty of water entered the inner system? Something like KIC 12557548.

http://www.space.com/15849-disintegrating-alien-planet-kepler-mission.html

If the orbit change was recent and chaotic, could it leave behind a trail big and wide enough as to obscure the star in such a way? I always wondered how massive would be a tail for something like a Pluto if it fell below the ice line due to some disturbance. And in that system there is a second star some 885AU away, so something like a Sedna (936 AU of aphelion) could be disturbed and end up falling onto the main.

Let's make some comparison to see the numbers. Halley comet has a mean diameter of 11km, with dimensions of 15x8 km. I found some old calculations that suggest a mass loss of 1.8x10_8 metric tons per appearance. We are talking of a comet that approaches the Sun 0.58 AU, and with an expected life of around 40 more appearances, so it's pretty unstable in cosmic terms, but still gives a good idea of the survivavility of such body.

In comets outgassing is caused not only in the surface, but also by the heating of its interior as demonstrated by Rosetta and the jets that appeared in the night side of 67P. Still, we can make - for the sake of making some rough numbers - an approximation to relate mass loss and comet surface. With these numbers, for something the size of - to give some known thing - Ceres, we could relate mass losses by that formula. Of course, we are assuming similar compositions, which we know is not true for Ceres and Halley.

A(sphere) = 4πr_2

Halley (5.5 km_2): 380km_2
Ceres: 2.770.000 km_2

So something the size of Ceres could lose 7300 more mass per visit to the inner solar system. Using the equivalences above, that would be a mass loss of 1.3x10_12 tons per transit.

With a mass so significantly higher than a comet, though, such a body could also be a lot more stable over time. Let's calculate how many orbits would be needed to lose 10% of the mass of such a body if its density was 0.5 g/cm3. Ceres has a mass of 9.393x10_20 kg at 2.16g/cm3 density, so at the density of a comet (more valid for the surface conditions than for the inner rocky mantle) of such a body, we would have an equivalent comet four times lighter, at 2.4x10_20 kg. 10% mass loss would then be 2.4x10_16 metric tons.

So for a mass loss of 10%, we get a value of at approx. 20.000 orbits. At 750 days period that would mean 40.000 years to lose that 10% of mass.

Something like Pluto, 15 times more massive than Ceres, would take probably 10-15 times more time to lose 10% of its mass, giving the possible value for a full disintegration somewhere around 4 million years.

Of course, a period of just 2 years is not plausible for such bodies, which should be born beyond the ice lines and have far longer orbital periods. At 80 years of orbital period we are talking of 160 million years for a full disintegration. That could account for the lifetime of this star, and be a remnant of its chaotic birth.

In any case, such a body would create a massive tail that could obscure the inner system. Not only that, after detaching from the main body, the tiny particles could be subject to the gravity well of passing planets, creating clouds of dust trailing them over the centuries. Planetary gravity wells could very well form trails of their own of huge sizes. I have no idea on how long would they survive, and how opaque they could become, but the peaks may indicate clouds born from different tails created by different orbits of the diving massive comet.

Furthermore, we know very little about the companion star. If the companion is in a circular orbit is one thing, but if it is in an elongated orbit like Sedna, the main star would be bombed by all icy objects from its outer regions constantly. The same could be possible for the companion, so a good indicator would be check the magnitude variations of the companion star.

For a star passing by at that distance, the disturbance would probably be self-explained by the massive infalling material from the outer parts of that system.

Posted by: ngunn Oct 20 2015, 09:54 PM

I'm still not buying the comets idea, sorry.

Posted by: silylene Oct 21 2015, 03:33 PM

QUOTE (JRehling @ Oct 16 2015, 05:27 PM) *
.....
And that scenario with rings that we see face-on from Earth would be provided only if the rings were perpendicular to the planet's orbit, which is unlikely to occur by chance; any deviation from that geometry would require a still larger ring system to provide the observed darkening.

That might just work if we only had one such event to explain, but four of them means that there would be at least three different giant planets with three gigantic ring systems. I can't see how that would happen.


Yes, I am proposing a complicated planetary system with multiple planets with giant ringed systems (at least 3 were observed), plus some planets without ringed systems for the minor occultations, and perhaps even additional exomoons, because if you look closely at the data, there are some shoulder spikes.

And yes, the ring system of the largest one would be 3-5x bigger than Saturn. [I want to remind that exoplanet J1407V has a ringed system 200x larger than Saturn.]

Also ringed object may be more of the rule, rather than the exception. Jupiter, Saturn and Uranus all have rings, although only Saturn has huge opaque rings. Neptune has arcs. At least one and two minor planets have rings (Charliko and 2060 Chiron).

Yes, what I proposed is complicated. I completely agree. And unlikely, I also agree. Perhaps this is why we have only seen *one* of these kinds of systems, it is unlikely?!

But perhaps what I propose remains more likely than other possibilities than odd planet-sized comets which don't absorb in the IR, orbiting rock swarms which are weirdly cold and opaque, or woo proposals which I refuse to consider.

I would like to understand better the long-term stability of large ringed systems in a complex solar system with several large planets and their gravitational interactions. I do suspect that one could have several "super-Saturns" and this would be a stable system.

Posted by: JRehling Oct 21 2015, 04:04 PM

The biggest problem with the rings hypothesis is this:

The rings would be invisible if the rings are in the plane of the planet's orbit. So, the rings must be closer to perpendicular to the plane of the planet's orbit... and, coincidentally, transiting the star near the node when we see them face-on. (Rings perpendicular to the planet's orbit would still appear edge-on to us much of the time. Consider Uranus as an example: The geometry is similar.) And, this is happening with not just one planet, but at least three. So, we're not just getting lucky once or twice, but about eight unrelated times.

If we saw just one of these, I would buy the rings hypothesis in a heartbeat. Three in one system and none anywhere else? No, this seems definitely wrong.

Posted by: Explorer1 Oct 21 2015, 04:13 PM

But as long as the parent planet's spin axis is pointed towards us, wouldn't the rings be perpendicular through the entire orbit? Uranus doesn't seem like a good example considering it orbits the sun, and its axis is pointed at us only twice each time.
Here's how I'm imagining it: point a finger at something far away, and then move your arm in a circle in front of you. The finger is the spin axis, the hand is the planet and rings, and the circle is the orbit.

Posted by: HSchirmer Oct 21 2015, 04:31 PM

QUOTE (silylene @ Oct 21 2015, 03:33 PM) *
Yes, I am proposing a complicated planetary system with multiple planets with giant ringed systems (at least 3 were observed), plus some planets without ringed systems for the minor occultations, and perhaps even additional exomoons, because if you look closely at the data, there are some shoulder spikes.
...


Actually, that might fit.


Binary Saturns.

Penn State has https://sites.psu.edu/astrowright/2015/10/15/kic-8462852wheres-the-flux/
but has also posted the light curves for this star.


[img]

Basically -the WTF star (above) looks totally different from the usual transit (below)




1) Usually, only a fraction to about 1% of the star is blocked.
-Here, almost 15 to 20 percent of the starlight is blocked. Whatever is causing the shadows is huge. Something around 55 jupiters across.

2) Usually, the light curve has steep sides as the object starts to move infront of the star, then a a flat "floor" as the object moves across the star, and another steep slope moves away from the star.
- This is different, the light curve has no floor. That suggests we are only seeing a portion of the object pass infront of the star. Whatever it is, it appears that we are only seeing PART of it pass in front of the star, not the entire silouhette.

Best-non-comet-guess? Binary gas giants with rings, edge on?
Yes, unlikely alignment, but this is an unlikely world.
Perhaps this is a pair of binary Saturns, tilted like Uranus, Pluto and Charon, but with a huge ring system.
Think of binary gas giants, each with Saturn's rings, but like Pluto & Charon, a double planet. Oh, and like Uranus and P&C, tilted ~90 degrees.

Kepler's day ~780 event is seeing one gas with maximum ring occultation but missing the other.
The day ~1510 even it seeing the one gas giant edge with maximum ring occultation, then seeing the other.
(yes, epicycles and deferents by another name....)
So, if you have binary gas giants in a loose orbit, you might have a some interesting periodicity.

Posted by: Mongo Oct 21 2015, 04:35 PM

QUOTE (Explorer1 @ Oct 21 2015, 04:13 PM) *
But as long as the parent planet's spin axis is pointed towards us, wouldn't the rings be perpendicular through the entire orbit? Uranus doesn't seem like a good example considering it orbits the sun, and its axis is pointed at us only twice each time.
Here's how I'm imagining it: point a finger at something far away, and then move your arm in a circle in front of you. The finger is the spin axis, the hand is the planet and rings, and the circle is the orbit.


But the planet transits the star, so the axis of the rings must be more-or-less perpendicular to the axis of the planet's orbit -- and also pointed at Earth -- with at least three separate objects. One is easy to believe -- it happens in our own solar system with Uranus -- but three, all with their axis pointing at Earth? Sound unlikely to me.

On the other hand, this phenomenon is quite unlikely already, otherwise we would have seen other examples before this.

Posted by: HSchirmer Oct 21 2015, 05:30 PM

QUOTE (Mongo @ Oct 21 2015, 04:35 PM) *
But the planet transits the star


Which is a bit of a "founder effect" for Kepler, it only picks out transiting stars...

QUOTE (Mongo @ Oct 21 2015, 04:35 PM) *
, so the axis of the rings must be more-or-less perpendicular to the axis of the planet's orbit


Well, we have that with Uranus and Pluto-Charon. Given the putative size of the ring system here, 55 jupiters across,
it's still going to be huge if viewed at 45 degrees or 30 degrees.

Actually, when I read over this, and thought about the denisty of a ring system or an asteroid belt, I was reminded of the proposals for a 'kamikaze' asteroid belt prob- IIRC something that would start from a solar polar orbit and then make a wrong-way run through the asteroid belt to maximize the number of imaging targets.

Basically, if you view a ring or belt edge on, you may get a rather high density of objects in view.

QUOTE (Mongo @ Oct 21 2015, 04:35 PM) *
with at least three separate objects.
One is easy to believe -- it happens in our own solar system with Uranus we would have seen other examples before this.


Well, as I speculated above, what about a binary gas giant, both with rings.
That would naturally create mulitple occulting objects in the same plane.

Posted by: Explorer1 Oct 21 2015, 05:43 PM

And now a star getting 40% of its light blocked: http://www.cbc.ca/news/technology/white-dwarf-asteroid-1.3282014
A white dwarf, so less need for dramatic explanations, in a small object, but quite interesting nevertheless! Definitely a tail in this case...
Paper: http://www.nature.com/nature/journal/v526/n7574/full/nature15527.html

Posted by: silylene Oct 21 2015, 06:57 PM

My concept is that the rings are not edge-on to earth (of course), but tilted as described earlier, as in the Uranus or Pluto-Charon system.

Yes this star would require 3 super-Saturns with the ring planes titled at high angles to the ecliptic. Agreed. Unlikely? Yes. But then we have Uranus and Pluto-Charon. For the sun, 25% of the large planets have a highly inclined orientation. 75% of the large planets have continuous rings. 25% of the large planets have huge opaque rings.


Now we get down to likelihood. A SWAG could be made just using the above numbers, but for a starting point, I would need to know the average number of large planets orbiting a star which is observed to have planets (it's in the Kepler data, I just don't know it).

I bet the result is rare...maybe 0.1% or something like that.

But then of all the thousands of systems Kepler has found, so far we have found just one system like this.

Posted by: alan Oct 21 2015, 07:33 PM

The asymmetry of one of the transits reminds me of the tadpole orbits Jupiter trojans follow relative to Jupiter position. It would require much more mass than in these orbits than in the present solar system, or it most of it to be distributed among smaller objects. I note that the wikipedia article on https://en.wikipedia.org/wiki/Jupiter_trojan references a model wherein Jupiter might have captured a much larger mass as trojans as it rapidly grew. If these were then broken up by collisions they may block enough light.

Posted by: JRehling Oct 22 2015, 12:40 AM

QUOTE (silylene @ Oct 21 2015, 11:57 AM) *
Yes this star would require 3 super-Saturns with the ring planes titled at high angles to the ecliptic. Agreed. Unlikely? Yes. But then we have Uranus and Pluto-Charon. For the sun, 25% of the large planets have a highly inclined orientation.


That doesn't begin to capture it. The case we've observed would require that the ring systems be highly inclined and relatively face-on as seen from Earth and highly inclined in the same way. It is not at all a given that two highly inclined (with regard to their star) systems would have poles that are mutually relatively aligned and face-on to Earth, much less that three or four would! And all be transiting. This isn't a couple of coincidences or a few coincidences; it's a barrel full of coincidences.

Basically, five or more axes would have to be co-aligned for no damned good reason. Not merely highly inclined WRT their orbits, but highly inclined WRT their orbits and co-aligned WRT one another.

If we see five of these coincidences in one system, we ought to be seeing two or three of them in orders of magnitudes more systems, and we aren't.

Posted by: AndyG Oct 22 2015, 08:37 AM

Huge, dense and opaque ring systems that are tilted during a transit: wouldn't there be a noticeable slight rise in apparent stellar brightness when this planet was near the star, half a year later?

Andy

Posted by: JRehling Oct 22 2015, 08:54 AM

QUOTE (AndyG @ Oct 22 2015, 01:37 AM) *
Huge, dense and opaque ring systems that are tilted during a transit: wouldn't there be a noticeable slight rise in apparent stellar brightness when this planet was near the star, half a year later?


If such a planet were in a circular orbit, yes. The surge due to a planet's reflected light is routinely detected by Kepler for Hot Jupiters. But: How much of the star's light is blocked does not depend upon the star-planet transit, but how much light is reflected by the planet varies with the inverse square of the distance. So, a planet+ring system with a cross section of 50 Jupiters out at a distance of 5 AU would reflect back as much light as a single Jupiter-sized planet with no rings at a distance of 0.8 AU, and much less than such a planet at 0.1 AU.

But, you raise an excellent point. A system packed with giant ring systems could conceivably avoid those surges, but the likelihood of it fitting our observation – already very low – is still another few notches lower given what you've pointed out.

That may say something about the comet-swarm hypothesis as well: If this star has gargantuan numbers of comets blocking its light, the comets performing that should also be reflecting a lot of light. These things should be – at least at times, and from some geometry – contending with the star itself in brightness, and we see nothing like that. I think you've made a great observation that undermines the comet hypothesis, too.

Explanations that would not produce a surge – if the clouds of occluding material were of low albedo, or quite far from the star, such as in another star system which is coincidentally aligned.

Posted by: HSchirmer Oct 23 2015, 12:33 PM

QUOTE (JRehling @ Oct 22 2015, 12:40 AM) *
If we see five of these coincidences in one system, we ought to be seeing two or three of them in orders of magnitudes more systems, and we aren't.



Something just occurred to me

"If we see" isn't necessarily the question..
When might we next see something?
That's a better question.

Looks like the effects have a 2 year period, occultations occurred in 2009, 2011, 2013

http://arstechnica.com/science/2015/10/something-were-not-sure-what-is-radically-dimming-a-stars-light/

So, it is 2015 now, is that putative 2015 occulation coming up, or has it already occurred?
Guess there will be alot of glass pointed that way this year...

Hmm, hubble has taken some planetary nebula photos at 1,400 LY


So, what size objects hubble can resolve, (not worded quite right) well, what size objects can hubble detect...

Posted by: Hungry4info Oct 23 2015, 01:10 PM

The relevant question is angular resolution, but that's not the right avenue of investigation. The discovery paper shows some good imagery of the star with a ground-based telescope, showing the star to have a companion. Transmission spectroscopy would make more sense here.

Posted by: Explorer1 Oct 31 2015, 02:17 AM

I was browsing the extreme exoplanets list on Wikipedia and stumbled upon this; it has to be a measurement mistake, right? https://en.wikipedia.org/wiki/K2-22b.
It would be denser then the element mercury and have around 70 G surface gravity, if true! Like that old Hal Clement novel....
NASA page here: http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=K2-22+b&type=CONFIRMED_PLANET

Posted by: Hungry4info Oct 31 2015, 04:27 AM

No, it isn't right at all. The original paper used those mass and radius values as upper limits, because not only is the planet too small to detect in transit, but it's also too low in mass to detect with RV. The planet is one of those tiny (sub-)Mercury planets that are evaporating large amounts of dust into space and producing an anomalous transit light curve. This feature requires a rather low surface gravity.

The K2-ESPRINT Project. I. Discovery of the Disintegrating Rocky Planet K2-22b with a Cometary Head and Leading Tail
http://arxiv.org/abs/1504.04379v2

The mass and radius values come from Table 4.

Update. I have corrected the Wikipedia article.

Posted by: Explorer1 Oct 31 2015, 06:52 AM

Yes, just as I suspected. I did a quick search t to find out if there were any journal articles, but found nothing. Looks like yet again truth is stranger than (science) fiction.

Posted by: JRehling Nov 2 2015, 05:01 PM

There are probably some planets made largely/entirely of gaseous rock and/or metal, which is pretty strange to consider. But I'd be very surprised if we find any planets much denser than iron (that is, iron's various denser states, under pressure). Iron is far more common than any elements heavier than iron, and I can't think of many processes that would discard iron and keep the heavier stuff. The center of the Earth's core is modeled to have a density of about 14 g/cm^3. I think the absolute maximum for any extrasolar planets would be around that level or less.

Posted by: HSchirmer Nov 3 2015, 03:44 AM

QUOTE (JRehling @ Nov 2 2015, 05:01 PM) *
...I can't think of many processes that would discard iron and keep the heavier stuff.
... I think the absolute maximum for any extrasolar planets would be around that level or less.


Well, what about a white dwarf that hits something and goes splat.

So, is there an inverse of the Chandrashekar limit, that requires small pieces of electron degenerate matter revert to "ordinary" matter below a specific mass? I recall theories about chunks of material made with charmed or strange quark properties remaining stable once formed

Posted by: JRehling Nov 3 2015, 04:20 PM

QUOTE (HSchirmer @ Nov 2 2015, 08:44 PM) *
Well, what about a white dwarf that hits something and goes splat.


The escape velocity of a white dwarf is about 6,000 km/s, white dwarfs have a mass of over 100 Jupiters, and collisions are inelastic. That is never going to produce planets.

Posted by: HSchirmer Nov 3 2015, 04:59 PM

QUOTE (JRehling @ Nov 3 2015, 04:20 PM) *
The escape velocity of a white dwarf is about 6,000 km/s, white dwarfs have a mass of over 100 Jupiters, and collisions are inelastic. That is never going to produce planets.


Agreed. You can't hit a white dwarf and break it up, unless you have a really big hammer.
Consider a white dwarf in a loose binary system where the other star goes supernova.
That shock wave should disrupt the dwarf, possibly leaving planetary mass chunks, or blasting it into smaller chunks.
Since we see planets around pulsars, even after a supernova, the disrupted material should reform planetary mass objects.

I'm not sure what the minimum gravitational force is to keep degenerate matter "packed down", thinking about it, it would seem
that the degenerate matter would "re inflate" violently when a white dwarf is disrupted.

Posted by: JRehling Nov 3 2015, 07:19 PM

QUOTE (HSchirmer @ Nov 3 2015, 09:59 AM) *
Consider a white dwarf in a loose binary system where the other star goes supernova.
That shock wave should disrupt the dwarf, possibly leaving planetary mass chunks, or blasting it into smaller chunks.


It's probably not the strongest use of this board to offer qualitative assumptions about never-observed phenomena. The outcomes of huge, cosmic collisions require pretty detailed research to determine, and math-free estimates of how they would proceed doesn't seem likely to be productive. A little math suggests to me that a supernova would not break a white dwarf apart, but that's not really on-topic for this board even if the issue were investigated thoroughly, much less when assumptions are made without math.

Posted by: Hungry4info Nov 3 2015, 07:48 PM

Besides, we know of numerous pulsar+WD binaries.

Posted by: nprev Nov 4 2015, 02:24 AM

JRehling is correct. Please stay on topic.

Posted by: ZLD Nov 25 2015, 05:36 PM

JPL http://www.jpl.nasa.gov/news/news.php?feature=4777 further suggesting the comet swarm hypothesis for the strange occurrence with KIC 8462852. The referenced paper is http://iopscience.iop.org/article/10.1088/2041-8205/814/1/L15?fromSearchPage=true for those with access. The reasoning is a continued lack of infrared evidence that would point toward other possibilities, mainly the breakup of a large rocky body.

Posted by: Mongo Nov 26 2015, 01:49 AM

Paper is up on ARXIV now:

http://arxiv.org/abs/1511.07908

QUOTE
We analyzed the warm Spitzer/IRAC data of KIC 8462852. We found no evidence of infrared excess at 3.6 micron and a small excess of 0.43 +/- 0.18 mJy at 4.5 micron, below the 3 sigma threshold necessary to claim a detection. The lack of strong infrared excess 2 years after the events responsible for the unusual light curve observed by Kepler, further disfavors the scenarios involving a catastrophic collision in a KIC 8462852 asteroid belt, a giant impact disrupting a planet in the system or a population of a dust-enshrouded planetesimals. The scenario invoking the fragmentation of a family of comets on a highly elliptical orbit is instead consistent with the lack of strong infrared excess found by our analysis.

Posted by: Mongo Jan 14 2016, 02:22 AM

http://"http://arxiv.org/abs/1601.03256"

QUOTE
The star KIC 8462852 is a completely-ordinary F3 main sequence star, except that the light curve from the Kepler spacecraft shows episodes of unique and inexplicable day-long dips with up to 20% dimming. Here, I provide a light curve of 1232 Johnson B-band magnitudes from 1890 to 1989 taken from archival photographic plates at Harvard. KIC 8462852 displays a highly significant and highly confident secular dimming at an average rate of 0.165+-0.013 magnitudes per century. From the early 1890s to the late 1980s, KIC 8462852 has faded by 0.193+-0.030 mag. This century-long dimming is completely unprecedented for any F-type main sequence star. So the Harvard light curve provides the first confirmation (past the several dips seen in the Kepler light curve alone) that KIC 8462852 has anything unusual going on. The century-long dimming and the day-long dips are both just extreme ends of a spectrum of timescales for unique dimming events, so by Ockham's Razor, all this is produced by one physical mechanism. This one mechanism does not appear as any isolated catastrophic event in the last century, but rather must be some ongoing process with continuous effects. Within the context of dust-occultation models, the century-long dimming trend requires 10^4 to 10^7 times as much dust as for the one deepest Kepler dip. Within the context of the comet-family idea, the century-long dimming trend requires an estimated 648,000 giant comets (each with 200 km diameter) all orchestrated to pass in front of the star within the last century.


Okay, this is unexpected. Clearly, something very weird is going on around this star.

A decline of 0.193 magnitude over a century equals a drop of 16.3%!


Posted by: nprev Jan 14 2016, 02:33 AM

Interesting. First thing this makes me think of is a close hot super-Jupiter that is shedding mass at a rapid rate, though constant over the observation period.

Posted by: Mongo Jan 14 2016, 02:54 AM

QUOTE (nprev @ Jan 14 2016, 02:33 AM) *
Interesting. First thing this makes me think of is a close hot super-Jupiter that is shedding mass at a rapid rate, though constant over the observation period.


It appears that no RV variations have been detected, as stated in the discovery paper. In addition, there is no IR flux as would be seen from an evaporating planet. From http://arxiv.org/abs/1512.00121:

QUOTE
Our observations are consistent with a normal main sequence star without sufficiently large amounts of circumstellar gas or dust, or inflowing or outflowing material, to produce a SpeX detection via the scattering or thermal re-radiation of the star’s insolation. Our observations have eliminated the possibility that there is a sizeable amount of very close-in, very hot (>1000 K) material along our line of sight to the star during the IRTF observations on 31 Oct 2015.

Posted by: nprev Jan 14 2016, 03:00 AM

Hmm. Curiouser indeed. Almost seems like it has to be something intrinsic with the star itself, then.

Posted by: ZLD Jan 14 2016, 03:07 PM

Clearly just Starkiller Base finishing checkout testing.

Joking aside, maybe this is a heavy element star that is fusing at a more rapid rate than it should be?

Also, what of the possibility of a small wandering black hole? Unfortunately, there doesn't seem to be any xray data of this area that I find. How close would a black hole need to get to start leeching material from the star and how obvious would that be initially in the first 100 years? Seems like it should be immediately when material hits the event horizon, x-rays would begin streaming out but if the intake is low still, would Chandra even be able to detect a faint stream of xrays?

I'm sure this star will turn out to be far more simple than anyone has yet proposed but if nothing else, its been good for getting people to talk about astronomy more.

Edit: Just to update on xray detection, the ROSAT data set has xray coverage of this region and nothing jumps out.

Posted by: Gerald Jan 14 2016, 04:16 PM

Black holes (besides hypothesized primordial ones) have a minimum mass a few (1.5 to 3) solar masses, since they form by overcoming the https://en.wikipedia.org/wiki/Chandrasekhar_limit for neutron stars (https://en.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit). A Black Hole sufficiently close to a main sequence star to accrete its outer hull would form a fast-rotating binary system with the star, usually causing high radial velocities relative to Earth. This would cause a considerable oscillation of the Doppler shift of the spectrum of the star, and would hence be immediate by spectral observations.

Posted by: JRehling Jan 14 2016, 10:09 PM

I wonder if the reality is that the dimming occurred in two sharp declines, with relatively level plateaus before and after each of them. That's how the data points look to me. I have no idea what dynamic, inside or outside a star, might cause that.

Posted by: Mongo Jan 16 2016, 06:04 PM

I noticed this statement from the Bradley E. Schaefer paper:

QUOTE
The long-term trend in the DASCH light curve can be described in various ways. One way is simply to note that KIC8462852 faded from B=12.2650.028 in 1892.5 to B=12.4580.012 in 1987.5, for a total fading of 0.1930.030 mag in 95 years. This fade rate is +0.2030.032 magnitudes per century (dashed line in Figure 1). This end-to-end trend line provides an excellent representation of all the Harvard data except for the decade from 1900-1909. The individual plates for this decade show a similar distribution of magnitudes as in adjacent decades, except that there are many more fainter magnitudes (from 12.6-13.0). This might be due to the star su ffering many deep dips during the years 1900-1909.


This sounds plausible to me. It would mean that there has been a quite steady decline in brightness over the periods covered by the plates (1890-1953 and 1969-1989) at a rate of about 0.203 magnitude per century. But during the time period 1900-1909, many of the observations showed lower than expected brightnesses, perhaps due to there being a lot more "dips" than in the other years. Many (most?) of the observations in those years were still in line with the 1890-1989 trend, though.

The author also stated that lower than expected brightnesses also occasionally happen at other times, so I assume that the observed rate of "dips" in the Kepler observations (2009-2013) would be consistent with the star's 1890-1900, 1910-1953 and 1969-1989 behavior.

In http://www.wowsignalpodcast.com/2016/01/season-3-episode-3-slow-and-fast.html Schaefer states that the only other comparable collection of plates to the Harvard Observatory collection that he had used, is the one created by the Sonneberg Observatory in Germany from the 1930s to the 1990s. This could be used to check the results found from the Harvard plate collection.

Posted by: Mongo Jan 16 2016, 06:39 PM

Okay, I've decided to download the full archive of Harvard Observatory observations of this object. I went to the http://dasch.rc.fas.harvard.edu/lightcurve.php page, and entered the object's coordinates: 20 06 15.457 +44 27 24.61 and got a text file that I converted to a spreadsheet file (which I tried to upload to this post, but it was not allowed).

I extracted the magnitude measurements with an RMS equal to or less than 0.2 (1265 data points) and created a chart with a second-order polynomial trend line:



There is a definite decline of about 0.2 magnitude (the trend line appears to underestimate this), but it also appears relatively flat from 1890 to 1953, and when observations resume in the late 1960s, the average brightness appears to be well below the earlier values and steadily declining.

Posted by: Mongo Jan 21 2016, 04:34 PM

Attached is a diagram I made using 2-year bins. I followed the same protocol as the author, with RMS <0.33 mag, AFLAGS <9000, and the measured magnitude more than 0.2 mag above the quoted plate limit. For each bin, I have a large dot indicating the average reading within that bin, plus smaller dots at one sigma standard deviation above and below that value.

The high reading for the 1969-1970 bin is due to a single high outlier, and for the 1989-1990 bin is due to two high outliers (there were a lot more measurements in the latter bin than in the earlier bin). If I remove those three outliers, those two bin magnitudes drop significantly, and become consistent with the other post-1962 bins.

I also added extra lines, indicating the averages plus one sigma standard deviations for all the measurements from 1890-1899, 1900-1952 and 1962-1989. The first time period from 1890 to 1899 definitely shows greater brightness than in the following 1900-1952 plateau. I have it as a plateau, but it visually looks like the brightness is declining over much of that decade.

Visually, the chart seems to show long periods of relatively steady brightness, separated by ~0.1 mag drops in the late 1890s and in the 1950s.

 

Posted by: dudley Jan 23 2016, 05:29 PM

KIC 8462852 is reportedly being watched for another instance of dimming. It was proposed to then analyze the light spectroscopically. It was indicated that this could determine if it was dust, or larger objects that were responsible for the dimming.
Dr. Schaefer's findings now seem to show that the star is already being substantially dimmed on a continuing basis. Wouldn't the spectroscopic work already done, which failed to find excess dust, indicate that larger objects cause the dimming? But what sort of larger objects?
Dr. Schaefer's work seems to call the cometary explanation into very serious doubt. Disrupted planets were already doubted, due to the absence of dust. Dimming of 15 and 22 percent suggest objects on the order of 500,000 to 700,000 miles in diameter. Single objects on this scale would appear to be stars, but no other conspicuously shining stars have been found very near KIC 8462852.

Posted by: nprev Jan 25 2016, 11:02 AM

In order to keep the Kepler topic open for other observations made specifically by that mission, this topic will be dedicated to this particular star.

Please review the Forum rules before posting. As I'm sure everyone knows there has been a tremendous amount of unconstrained speculation as well as an abnormal amount of anomalism in the popular press concerning this subject, but that will not be permitted here. Posts that do not meet Forum standards will be deleted.

Posted by: HSchirmer Jan 25 2016, 03:53 PM

QUOTE (dudley @ Jan 23 2016, 06:29 PM) *
KIC 8462852 is reportedly being watched for another instance of dimming.
It was proposed to then analyze the light spectroscopically. It was indicated that this could determine if it was dust, or larger objects that were responsible for the dimming.
...
Wouldn't the spectroscopic work already done, which failed to find excess dust,
indicate that larger objects cause the dimming? But what sort of larger objects?
...


I believe they thought "inner planet smash" and looked for excess infrared radiation,
didn't see it, and interpreted the lack of signal as the lack of hot dusty debris and concluded no inner planet collisions.
Next, hypothesis for dimming, without infrared, was a comet swarm on an elliptical orbit.
That doesn't seem to fit, it requires a staggering number of comets.
So, it may seem that we are left with a single large object as the 3rd choice.

However, does a lack of IR actually rule out large inner solar system collision?
We consider that additional cold dust further out might blocking starlight, how about blocking IR?
So, what if both #1 and #2 happened? Inner planet collision and comet dust that blocks that IR?

1) What are the chances that there is a planetary system around Tabby's star. Pretty good.
2) What are the chances that planets around Tabby's star could shift orbits? Given the large percentage of hot Jupiters and hot Neptunes that have been observed, pretty good.
3) What are the chances that shifting planets create dust and comet redistribution? Pretty good.
We know/suspect our solar system has been shuffled at some point, comets and asteroids and KBOs all shifted around.

The recent Planet 9 paper's authors did a prior paper about nice model / jumping Jupiter scenario. Their simulations showed that for a sun-sized star, the gas giants generally eject comets or planets from a solar system, while the ice giants generally scatter them around the solar system.

So, here's a mechanism to consider.
Tabby's star is a sun-sized solar system, similar amount of material, similar snow line.
It develops with ice giants but no gas giants, then it experiences planetary migration.
Because it does not have gas giants to scatter comets out to oort distances as long period comets,
Tabby's Star ends up with a massive kuiper belt, and we are seeing either a massive comet shower,
or actual planetary scattering.

So, my questions
What is the expected IR signal from an inner solar system disrupted rocky planet?
What level of comet dust would be necessary to absorb that IR signal?

Posted by: JRehling Jan 25 2016, 05:50 PM

The use of archival data to study the brightness variations lead me to another thought: How many other stars have shown this (or another) sort of hitherto-unexplained dimming? If we had data like this on KIC 8462852, and Kepler was only observing 1/400th of the sky, it is seemingly almost certain that more stars like this exist… depending on the definition of "like this."

Here are the basic observed facts about KIC 8462852, to summarize:

1) Progressive dimming over several decades, which may be occurring in steps rather than smoothly.
2) Sudden and reversible dimming on rare occasions during the Kepler observations. The baseline during this time was quite constant, and the dips occurred during a tiny fraction of the Kepler observations. The duration of these events was similar to planetary occultation, but the magnitude was anomalously large, the timing between them was irregular, and the shape of them was unlike any planet or star transit.
3) The IR spectra indicates that there is not a large amount of warm dust in the system.

The reason why the comet explanation seems to fit (2) and (3) is because comets spend almost all of their time far from the star, and so could absorb a bit of warmth in a small time and radiate it over a long time; the radiation must be re-radiated, but could happen at a longer wavelength than warm dust would.

To assimilate all of these into one exogenous explanation, all I can come up with is: KIC 8462852 is surrounded by a massive amount of material that is occulting it, to a considerable degree, all the time, but the individual particles are predominantly in highly elliptical orbits. Ongoing catastrophic events are generating progressively more occulting material, so the fraction of the star's light that is being blocked is increasing from an already-high degree to an even higher degree.

Alternately, something internal to the star may be occurring, and therein I have no insight to offer. As with the exogenous explanation, any endogenous cause must certainly be something rare and therefore unusual.

It's a puzzler. It's like astronomy as written by Agatha Christie.

Posted by: HSchirmer Jan 25 2016, 08:26 PM

QUOTE (JRehling @ Jan 25 2016, 05:50 PM) *
...
To assimilate all of these into one exogenous explanation, all I can come up with is: KIC 8462852 is surrounded by a massive amount of material that is occulting it, to a considerable degree, all the time, but the individual particles are predominantly in highly elliptical orbits. Ongoing catastrophic events are generating progressively more occulting material, so the fraction of the star's light that is being blocked is increasing from an already-high degree to an even higher degree.
...
It's a puzzler. It's like astronomy as written by Agatha Christie.


Well, just because a star is middle aged and main sequence, doesn't mean things with the planets
can't get, er, interesting....

QUOTE (On the Dynamical Stability of the Solar System)
Konstantin Batygin, Gregory Laughlin
(Submitted on 11 Apr 2008)

A long-term numerical integration of the classical Newtonian approximation to the planetary orbital motions
of the full Solar System (sun + 8 planets), spanning 20 Gyr, was performed.
...
The experiments yielded one evolution in which Mercury falls onto the Sun at ~1.261Gyr from now, and another in which Mercury and Venus collide in ~862Myr. In the latter solution, as a result of Mercury's unstable behavior, Mars was ejected from the Solar System at ~822Myr.

http://arxiv.org/abs/0804.1946


Apply that sort of scenario to Tabby's star, two rocky planets collide, a third is ejected (likely scattering comets)
and there ought to be plenty of material around to create long term and periodic dimming of the star.

Posted by: dudley Jan 25 2016, 10:04 PM

If I recall correctly, the Kepler Space telescope found no periodicities in the dips in light from this star. We're assuming, it seems, that the plane in which any planets, or their shattered debris would travel, aligns with the star from our point of view.

Even if two planets had collided and destroyed themselves, we might have expected other planets, or even just one, to be found, mightn't we? If there was a complete absence of planets around this star, these collisional scenarios would seem to be unworkable.

Posted by: JRehling Jan 25 2016, 11:27 PM

QUOTE (HSchirmer @ Jan 25 2016, 01:26 PM) *
Apply that sort of scenario to Tabby's star, two rocky planets collide, a third is ejected (likely scattering comets)
and there ought to be plenty of material around to create long term and periodic dimming of the star.


If two rocky planets collided to create lots of material, then there should be an IR signal as the material re-emits, at longer wavelengths, the visible light that it absorbs. But observations contradict that possibility.

That is, if planets orbiting relatively close-in did so. I agree that a catastrophe located much farther out might be part of the answer, but then it must have generated a truly tremendous amount of material to be covering much of the star, continuously.

Posted by: JRehling Jan 25 2016, 11:29 PM

Kepler found no planets around this star, but that doesn't mean that there are no planets. Kepler can miss a planet larger than Earth even if it transits a star, because the signal-to-noise ratio can be sub-threshold. It can certainly miss a bunch of Mars-sized planets. And it could even miss a whole host of planets that almost transit a star while the debris from a collision, slightly off that plane, does transit the star.

Posted by: HSchirmer Jan 26 2016, 12:52 AM

QUOTE (dudley @ Jan 25 2016, 10:04 PM) *
If I recall correctly, the Kepler Space telescope found no periodicities in the dips in light from this star. We're assuming, it seems, that the plane in which any planets, or their shattered debris would travel, aligns with the star from our point of view.


The did see something with a 750 day period.
For reference, mars' orbit is 687 days, so assuming the "something big" is in orbit,
that would be, eh, roughly around the inner edge of our asteroid belt.

QUOTE (dudley @ Jan 25 2016, 10:04 PM) *
Even if two planets had collided and destroyed themselves, we might have expected other planets, or even just one, to be found, mightn't we? If there was a complete absence of planets around this star, these collisional scenarios would seem to be unworkable.


Brilliant question!
Complex answer.

Rephrased-
"If Kepler was looking at our own solar system from Tabby's planet, how many of our planets would it see transit?"

If all the planets around a sun have the same angle, and the same 'phase' (argument of perihelion?) then yes.
In practice, no.

Here are our planet's orbital tilts relative to earth.

Mercury 7.01°
Venus 3.39°
Earth 0
Mars 1.85°
Jupiter 1.31°
Saturn 2.49°
Uranus 0.77°
Neptune 1.77°
https://en.wikipedia.org/wiki/Orbital_inclination

It's a difference of a few degrees, but at several million KM away from the sun, a small angle leads to
a big distance above or below the orbital plane.

And, each tilt is going to be oriented in a different direction-
imagine looking down at the solar system as if it were a compass.
So, Mercury's tilt is above the plane towards North and below towards South,
but Venus' might be above at East and below at West.

Another way to think about it- why are solar eclipses special?
Even though we have a (relatively) large moon, that is close to the same plane as the sun,
it's actually quite rare for the orbit of the moon to line up with the orbit of the sun.

Posted by: dudley Jan 26 2016, 01:47 AM

QUOTE (JRehling @ Jan 26 2016, 12:27 AM) *
If two rocky planets collided to create lots of material, then there should be an IR signal as the material re-emits, at longer wavelengths, the visible light that it absorbs. But observations contradict that possibility.

That is, if planets orbiting relatively close-in did so. I agree that a catastrophe located much farther out might be part of the answer, but then it must have generated a truly tremendous amount of material to be covering much of the star, continuously.


So, suppose two super-Earth sized rocky planets were ejected to the outer part of that star system, and then happened to collide very recently. Could that be a reasonable scenario? Could this create a distant debris cloud sufficient to account for the observed century-long dimming trend, yet not produce a conspicuous infra red signature from the dust? Could localized denser patches in that debris cloud maintain themselves long enough to also account for the instances of short term dimming?

Posted by: JRehling Jan 26 2016, 08:47 AM

QUOTE (dudley @ Jan 25 2016, 06:47 PM) *
So, suppose two super-Earth sized rocky planets were ejected to the outer part of that star system, and then happened to collide very recently. Could that be a reasonable scenario? Could this create a distant debris cloud sufficient to account for the observed century-long dimming trend, yet not produce a conspicuous infra red signature from the dust? Could localized denser patches in that debris cloud maintain themselves long enough to also account for the instances of short term dimming?


Inner planets are not ejected into orbits with periapses much farther out than the body that ejected them. They are either sent into elliptical orbits that return to the inner system or they are ejected from the system entirely. The answers to the other questions you ask are less clear to me, anyway.

Posted by: JRehling Jan 26 2016, 09:20 AM

QUOTE (HSchirmer @ Jan 25 2016, 05:52 PM) *
The did see something with a 750 day period.


No. The first dip, which by itself resembled one planetary transit, was seen at mission day ~792 and then a very strange series of several dips took place roughly from days 1510 to 1570. Nothing in the later series of dips is obviously a repeat of the first observed dimming event. The paper has a section discussing the possibility of the second event being related to the first, with a ~750 day period; in the discussion, that possibility is called "problematic." Follow-up observations showing a lack of IR excess further discredit that possibility.

Without a third observation, the inference that two light curve dips indicate one specific "something" is doubtful even in a less strange case. An observer elsewhere could see Venus and Earth both transit the Sun, but wouldn't know whether those two transits were caused by one planet or two planets until a third transit was seen.

Whatever was seen between days ~1510-1570 was seen only once, and what was seen at day ~792 was not obviously seen even one more time, much less two more times.

Posted by: HSchirmer Jan 26 2016, 02:56 PM

QUOTE (JRehling @ Jan 26 2016, 10:20 AM) *
No. The first dip, which by itself resembled one planetary transit, was seen at mission day ~792 and then a very strange series of several dips took place roughly from days 1510 to 1570. Nothing in the later series of dips is obviously a repeat of the first observed dimming event. The paper has a section discussing the possibility of the second event being related to the first, with a ~750 day period; in the discussion, that possibility is called "problematic."
...


Yep, I should have said "they're looking" at a 750 day period, but more data is needed.




QUOTE (dudley)
So, suppose two super-Earth sized rocky planets were ejected to the outer part of that star system, and then happened to collide very recently. Could that be a reasonable scenario?


Eh, I think that would be overkill.
The paper mentions that you don't need a really huge impactor to create a suitable dust cloud-


It's not that hard to conceptualize an area where several 100 km objects orbit, we call it https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size#From_100_to_200_km The problem seems to be that there is no known mechanism for comets or asteroids to break up in a coordinated manner to generate the 100 year dimming, or the series of Kepler dips. The papers about KIC 8462852 follow current ideas about comets and assume that extra-solar comet clouds have stable circular orbits which require passing stars to trigger comet showers.

That's why I though the comet-ejected-by-gas-giant versus comet-scattered-by-ice-giant issue was interesting.
It's a tangent about the circularization of hyperbolic comet orbits to create the Oort cloud. The rule stated above
QUOTE (JReheling)
Inner planets are not ejected into orbits with periapses much farther out than the body that ejected them. They are either sent into elliptical orbits that return to the inner system or they are ejected from the system entirely.
doesn't seem to apply to Oort cloud comets. Comets that were ejected from the solar system are though to somehow have circular orbits which require another perturbation to return them to the inner solar system.

Computer simulations of our solar system suggest that 1) planets like to form near the "snow line" where ices first condense, 2) planets can shift because of orbital resonances, and 3) when planets shift they toss lots of small stuff like comets around. Gas giants like Jupiter and Saturn have enough gravity to scatter comets so far out (50k - 100k au) that the comets stay out there in the Oort cloud, and the https://en.wikipedia.org/wiki/Oort_cloud In contrast, when ice giants like Uranus and Neptune scatter comets, they don't go as far and are assumed to return along the elliptical orbits they started on.

Point is: current theories about Sol like systems indicate that when planets shift with gas giant(s) to eject comets you end up with 5 earth masses of comets into trillions of distant, stable, circular orbits. Then you need a passing star to disturb those circular orbits and create killer comet showers. However, it seems that ice giants only scatter comets, so you should end up with 5 earth masses of comets into trillions of nearby, unstable, elliptical orbits. Then you don't need any second event to get killer comet showers.
So, could KIC 8462852 be the model for a "https://en.wikipedia.org/wiki/Kessler_syndrome" solar system?

Posted by: dudley Jan 26 2016, 11:25 PM

I wonder if trillions of comets, especially after colliding and reducing themselves to bits, wouldn't make for a uniform debris field around a star, rather than one comprised of distinct clumps of material. The latter is what seems to be present at KIC 8462852.
I also wonder if perturbations of comets by Neptune-mass planets would be great enough over a single century, so as to account for a fairly steady dimming of the star's light by about one fifth.

Posted by: HSchirmer Jan 27 2016, 12:21 AM

QUOTE (dudley @ Jan 26 2016, 11:25 PM) *
I wonder if trillions of comets, especially after colliding and reducing themselves to bits, wouldn't make for a uniform debris field around a star, rather than one comprised of distinct clumps of material. The latter is what seems to be present at KIC 8462852.
I also wonder if perturbations of comets by Neptune-mass planets would be great enough over a single century, so as to account for a fairly steady dimming of the star's light by about one fifth.


That's the nice thing about power laws, they provide a baseline of many small events, and the occasional whopper..

As for exo-kuiper belt objects smacking rocky planets, we think we've seen http://www.space.com/13329-alien-solar-system-comet-bombardment.html that result in big hits on inner solar system planets.

That system, https://en.wikipedia.org/wiki/Eta_Corvi has an interesting alignment, we see two bands of dust- hot and cold. The hot band at 3 AU is interpreted as a transient result of a single strike from a kuiper belt sized object hitting a rocky planet. The cold band around 150 AU is interpreted as a long term result of kuiper belt collisions as a result of an outer planet migrating through that area.

Posted by: JRehling Jan 27 2016, 12:22 AM

During the Kepler era, KIC 8462852's brightness seems quite constant most of the time. If this represents the same luminosity star as it was 100 years ago, perpetually dimmed by some debris between us and it, there has to be a component of debris that is remarkably constant, and therefore fine, and can't be taking the form (most of the time) of large, individually significant chunks.

So, we'd have to have the star partially blocked by something like Saturn's rings (i.e., fine material, translucent, not necessarily shaped like rings), all the time, with bigger episodic events happening from time to time, and those "rings" would have to be pretty far from the star most of the time in order for the IR observations to turn up nothing. That means that the material is either far from the star all the time in a relatively circular orbit (or spherical shell, or a thick belt between a plane and a sphere), or in an elliptical orbit that crosses in front of the star.

That seems odd, but the observational constraints don't allow for a lot of other exogenous explanations.

I'd like to hear of some endogenous explanations; it may be too much to ask at this time.

Posted by: HSchirmer Jan 27 2016, 02:20 AM

QUOTE (silylene @ Oct 21 2015, 03:33 PM) *
Yes, I am proposing a complicated planetary system with multiple planets with giant ringed systems (at least 3 were observed), plus some planets without ringed systems for the minor occultations, and perhaps even additional exomoons, because if you look closely at the data, there are some shoulder spikes.

And yes, the ring system of the largest one would be 3-5x bigger than Saturn. [I want to remind that exoplanet J1407V has a ringed system 200x larger than Saturn.]
...


Took a minute to review the posts on this thread, something now jumps out at me.
Rings.

If Tabby's star has comets and KBOs being scattered into the inner solar system, similar to our late heavy bombardment, then impacts on rocky planets could generate hot dust that could cause dips in the starlight. But, near misses should result in rings around the planets. And once you have rings around a planet, that should, in turn, increase the likelihood that the next passing comet will be intercepted as well.
Some work on the idea http://arxiv.org/abs/0809.5073 mentions that comet flux would be so large that "all satellites smaller than Mimas would have been destroyed during the LHB"




It would seem that a captured comet or KBO disintegrating into a ring won't generate the sort of heat signature that is generally associated with an impact.

And the ring orientation won't necessarily be around the planets equator / that system's ecliptic.
The ring orientation should depend on the angle of approach for the comet/kbo.

Posted by: stevesliva Jan 27 2016, 05:38 AM

QUOTE (JRehling @ Jan 26 2016, 08:22 PM) *
I'd like to hear of some endogenous explanations; it may be too much to ask at this time.


When I consult google on this, I find that the rotational rate is 0.88 days, and you see a wiggle with that frequency in the light curve. So with the big dramatic dips, if the dip itself doesn't have that 0.88 day period, then it can't be anything like giant starspots or shortlived metal clouds... it couldn't be *anything* constrained to the star's rotational period. So to be endogenous, it would almost have to be the star burping out its own veil. How else would something endogenous be so transient?

Or is the star's rotational pole in view, in which case a transient phenomenon at that pole could stay in view? Still, it looks like these dips are super-short. Maybe if it's the magnetic pole, it occasionally sucks in occulting materials. So it's like an opaque aurora viewed pole-on. So some sort of passing cloud of matter gets sucked in, turns into a very short-lived veil over the pole, and then dissipates. Which I guess would be an exogenous trigger.... anyways, I'm only speculating on the geometry of what would be endogenous, not the physics. Because I can't offer a physical explanation.

Posted by: Gerald Jan 27 2016, 11:11 AM

QUOTE (HSchirmer @ Jan 27 2016, 03:20 AM) *
...
Rings.
... But, near misses should result in rings around the planets. And once you have rings around a planet, that should, in turn, increase the likelihood that the next passing comet will be intercepted as well.

Dense rings around planets stay stable only within the https://en.wikipedia.org/wiki/Roche_limit.
That's the same zone where a passing body might disintegrate due to tidal forces.
There may be some increment by impacts due to the ring, but compared to the size of the stellar system, there should be something more impressive.
A collision or a very close near-miss of two planets might temporarily create a large cloud of debris or a dense ring around a star.

Posted by: Gerald Jan 27 2016, 11:21 AM

QUOTE (stevesliva @ Jan 27 2016, 06:38 AM) *
... So to be endogenous, it would almost have to be the star burping out its own veil. How else would something endogenous be so transient? ...

There exists a considerable variety of https://en.wikipedia.org/wiki/Variable_star#Intrinsic_variable_stars, caused by several kinds of oscillations.
https://en.wikipedia.org/wiki/Slow_irregular_variable show intrinsic variability which doesn't follow a regular pattern.
Superposition of several oscillations might look chaotic.

Posted by: HSchirmer Jan 27 2016, 02:16 PM

QUOTE (Gerald @ Jan 27 2016, 12:11 PM) *
Dense rings around planets stay stable only within the Roche limit.
That's the same zone where a passing body might disintegrate due to tidal forces.


Yes, agreed, but I'm not sure that "Roche stable" conveys the scope of things here.
The http://www.unmannedspaceflight.com/index.php?showtopic=8154&view=findpost&p=227479 does raise some good points about a big ring system (.8 AU) that blocks large amounts of light (95%) as a possible analog, notwithstanding that such a ring is not stable over astronomical periods of time.

QUOTE
Gigantic ring system around J1407b much larger, heavier than Saturn’s
http://www.rochester.edu/newscenter/gigantic-ring-system-around-j1407b
Astronomers expect that the rings will become thinner in the next several million years and eventually disappear as satellites form from the material in the disks.
..
In the case of J1407, we see the rings blocking as much as 95 percent of the light of this young Sun-like star for days,


Take the ring system around J1407B, an earth's worth (6 x 10^24 kg) of ring material around a gas-giant/brown dwarf. It's 120 million km wide (yes, 80% of an AU wide), up to 95% opaque, will be there for millions of years, but, it isn't stable. But, it is still a possible explanation or, at least, an interesting example of the upper range of possibilities.

Interestingly, ring systems might create some positive feedback, it seems they act sort of like a snow fence and thin rings can catch fine dust from passing comets. Recent work on ripples in the ring systems of Jupiter and Saturn http://www.nature.com/news/2011/110331/full/news.2011.198.html suggest that the Jovian and Saturnian ring systems can accumulate about 10^12 kg (Saturn) to 10^13 kg (Jupiter SL9) of dust per comet. In a dusty solar system, that could become quite a bit of material.

Point is, a nice model late heavy bombardment situation provides several mechanisms to block starlight.
In other systems we see cold dust clouds consistent with a collision cascade of KBO's, we see hot dust clouds consistent with KBO impacts on rocky planets, we see huge ring systems that stretch 80% of an AU and block up to 95% of the starlight. Looking at our own solar system, we have simulations that KBOs could put substantial ring systems (up to 1,000 times more massive than Saturn is now) around all four giant planets. We have simulations that the LHB comet flux might trigger shatter cascades in the asteroid belt. We find that planet moving resonances are not limited to the early solar system, we may yet have planetary collisions or mercury burning up as it is scattered into the sun, or mars ejected out through the Kuiper belt.

Posted by: dudley Jan 27 2016, 04:32 PM

I'm aware of two suggestions for how something happening within the star could affect its brightness. The one that can be discussed here has a small black hole becoming lodged inside the star, absorbing its material, and causing it to dim.
Supposing it's possible for a small black hole to assume and maintain such a position, it's not clear if its effects would be sufficient to account for observed long term dimming, or that the effect would vary enough, over short periods of time to explain the dips in brightness.

Posted by: JRehling Jan 27 2016, 06:26 PM

QUOTE (HSchirmer @ Jan 26 2016, 07:20 PM) *
But, near misses should result in rings around the planets.


Probably not. An object that passes close to a planet will not normally be captured by it. It will go into a stellar orbit that intersects the planet's orbit again in the future. Capture is a low-probability event.

If a huge swarm of objects flies by, maybe a significant fraction of them could end up in orbit, but if it's just one or even a dozen, that's not likely.

If a planet already has a sizable satellite, that could also disrupt the formation of any possible ring.

There are a lot of possible permutations. I don't think we're going to resolve them with qualitative pondering.

Posted by: stevesliva Jan 27 2016, 08:47 PM

I have been thinking a lot about the geometry and the rotation rate's signature in the light curve. Perhaps we're seeing a pole in the earth-facing hemisphere, and we're seeing a polar hood form and dissipate, with just part of the hood rotating out of view, to give the big dip some brighter shoulders. I think along these lines because crazy stuff like enormous starspots or metal clouds would show that 0.88 day rotation.

Polar phenomena like aurorae-- who knows what would cause a very transient one on a star? Not me. But it's interesting to think about, and do you call that endogenous if the trigger is exogenous, like on earth?

Posted by: Hungry4info Jan 28 2016, 01:27 AM

Occam strikes again. Looks like the long-term dimming is best explained by calibration issues.

KIC 8462852 did likely not fade during the last 100 years
http://arxiv.org/abs/1601.07314

Posted by: Explorer1 Jan 28 2016, 07:32 AM

So the modern dimming is just comets after all?

Posted by: silylene Jan 28 2016, 02:44 PM

I still think my earlier proposal (prior thread posts #10, #26 in this thread) of occultations by giant ringed planets is at least as equally likely as the alternative proposals of monstrous sized crashing comets or dust clouds from colliding giant asteroids. While I agree that a system with a couple of giant ringed planets tilted at angles off the ecliptic is unstable over eons of time, its lifetime and chance of observation seems more likely to me than the chance observation of the much more transient phenomena of the transiting giant comets or colliding asteroid dust cloud proposals.

Posted by: dudley Jan 28 2016, 05:31 PM

I'd like to see and consider Dr. Schaefer's response to the new paper by M. Hippke, and D. Angerhausen , before reaching any firm conclusions about the presence or absence of a century-long dimming of KIC 8462852. As an experienced stellar photometrist, Dr. Schaefer had previously observed that the Harvard Observatory work appeared reliably consistent over the long term.

Posted by: JRehling Jan 28 2016, 08:08 PM

stevesliva, I like your idea, although I don't know if there's any precedent for a star producing a hood that dims its brightness; yet, we must come back to the fact that whatever is happening is by definition very unusual.

If an endogenous cause is at work, it would either show a component of the 0.88-day period or be changing on a scale considerably faster than that.

It's interesting to consider the possible connectedness of the four dips:

What happened at day 792 resembles a single transit by one very large planet, although it is problematically large. Maybe it has a ring system, or maybe the derived parameters are erroneous. If it is a planet, it's almost certainly a big giant.

What happened at days 1510-1570 may be entirely unrelated to the day-792 event, something strange (like the comet swarm). Or, it may be a second pass by the object from day 792, with something catastrophic having happened in the meantime. This is a testable hypothesis: If such an object does exist, we know exactly when to look for more transits. Investigating that possibility is a must.

Posted by: Hungry4info Jan 28 2016, 10:11 PM

Response from Schaefer. Rather direct...
http://www.centauri-dreams.org/?p=34933

Posted by: JRehling Jan 29 2016, 12:24 AM

It seems like Schaefer has a definitively better grasp of the issue than his detractor.

I'm not sure why he said, "This dimming from the DASCH data is just a long-time scale version of the dimming also seen with the Kepler spacecraft…" but that may be nitpicking. Given one star and two anomalies, there's good reason to suspect that the anomalies might be related, but one of these, over a long timescale, is monotonic and the other, over a short timescale, was weirdly varying, and it's not certain that one is a version of the other.

However, I think we can go back to seeing this as a three-part mystery: The century-long dimming, the planet-like dimming event at one point, and the weird, up-and-down dimming about 740 days later.

Posted by: Gerald Jan 29 2016, 09:11 AM

Since intrinsic causes are considered unikely, as well as large numbers of large comets, but a single unknown cause is supposed in Schaefer's initial paper, I'm wondering whether kind of a http://adsabs.harvard.edu/full/1994A%26A...289..559L moving in front of the star, or interacting with the star, could catch the observations. Interaction might cause some detectable wobble, and is less likely due to lack of an infrared signature.
To explain lack of absorption and emission lines, the presumed globule should have been swept free of gas for some reason.

So, kind of an almost gas-free https://en.wikipedia.org/wiki/Bok_globule moving into the line of sight could be a construct explaining the observation.
Observation of visually close-by background stars might help to discern this kind of scenarios.

Posted by: JRehling Jan 29 2016, 07:37 PM

A Reddit chat about this phenomenon raised, and summarily rejected, the idea of a Bok globule:

https://www.reddit.com/r/IAmA/comments/3set9l/we_are_some_of_the_astrophysicists_and_planet/

The reasoning given is: "we can constrain the position of the globs to be as far as Jupiter is to our Sun, but likely not much farther."

Given the brevity of the response, I'm not sure if all parties understood one another. There is discussion of circumstellar clumps in the Boyajian, et al, paper, but I'm not sure how interstellar clumps are excluded.

Posted by: JRehling Jan 29 2016, 09:39 PM

I've found a statement of the problem with an "interstellar" explanation – that the occulting material/objects are located between Tabby's star and Earth. It's posted here:

http://sites.psu.edu/astrowright/2015/10/15/kic-8462852wheres-the-flux/

"It’s very hard to get an interstellar occulter model to work. In order for the occulter to be physically small, it would have to be much closer to the Solar System than the star. In that case, the parallax from Kepler’s motion around the Sun would enter into things, and you’re back to large mutual velocities, which means short timescales."

Posted by: dvandorn Jan 30 2016, 01:38 AM

A perfectly aligned stream of cometary bodies (or at least bodies of similar size), that was gravitationally liberated from some star system by a passing star or other massive body, could appear dark from Earth if there is no nearby star to light it up, and could be narrow enough that it would not occult other stars in the nearby starfield. It's the latter constraint, the lack of any abnormal dimming in the nearby starfield, that constrains the option of interstellar occulters more than anything else, but a one-in-a-billion configuration might result in such a stream of small bodies that would only occult the one star. Variations in its density along the stream could result in the odd ups and downs we are seeing -- the stream might be passing between us for some time, but only the densest stretches of it are detectable.

It's just not a very likely explanation, I fear.

Posted by: Gerald Jan 30 2016, 03:17 AM

It cannot be anything likely, since otherwise we would see many similar copies elsewhere.

The next idea I could offer would be two or more filters of rotating polarisation due to aligned interstellar dust in magnetic fields to explain the short dimming peaks.
As strange as it sounds, it seems something along these lines has been considered already, although maybe for different reasons.
(Pete Mancini, October 21, 2015 at 3:07 pm, in http://sites.psu.edu/astrowright/2015/10/15/kic-8462852wheres-the-flux/)

Other ideas would be https://en.wikipedia.org/wiki/Bandwidth-limited_pulse similar to a http://mathworld.wolfram.com/SincFunction.html by adding up oscillations of neightbouring frequencies, since we see both, small high-frequency oscillations and sudden peaks of dimming, e.g. by intrinsic infrasound waves,
and https://en.wikipedia.org/wiki/Mitchell_Feigenbaum-ish https://en.wikipedia.org/wiki/Bifurcation_diagram of a dynamical system hinted to by double- or triple dimming peaks, the physical realization unknown as of yet.

So we have the choice between various unlikely scenarios.

Posted by: JRehling Jan 30 2016, 03:55 AM

A problem with comets that are dark and far from any star is that they would therefore be cold and not generating tails, and therefore not producing so large of a cross section.

The same explanation could work if one imagines more material, but one of the appeals of the comet explanation in the first place was that they can generate a lot of cross section when warm.

Posted by: Gerald Jan 30 2016, 11:02 AM

The "it cannot be a young star due to the distance from star formation regions" argument, when thinking at intrinsic reasons, could be overcome by assuming a recent merger of a binary, or swallowing of a brown dwarf companion.
Such a merger may also explain the short rotation period.

When persuing the occultation scenario, the dimming events could be used to reconstruct properties of the structure of the cloud.

Posted by: dudley Jan 30 2016, 05:21 PM

The luminosity class of KIC 8462852 seems to be consistently given as V-IV. Does this indicate a star of considerable age, still on the main sequence, but soon, in the astronomical scale of things, to leave it? If so, the solar system debris associated with young stars, and something similar to our late heavy bombardment seem unlikely to play a part in the solution of this mystery.

Posted by: HSchirmer Jan 30 2016, 07:19 PM

QUOTE (dudley @ Jan 30 2016, 05:21 PM) *
The luminosity class of KIC 8462852 seems to be consistently given as V-IV. Does this indicate a star of considerable age, still on the main sequence, but soon, in the astronomical scale of things, to leave it? If so, the solar system debris associated with young stars, and something similar to our late heavy bombardment seem unlikely to play a part in the solution of this mystery.


Ok, I'm curious now, is there any definite framework or theory to correlate planetary arrangments and how long solar system debris stay around?
For example, IIRC, systems with hot Jupiters are assumed to have shovel everything else into the parent star in relatively short time frame, but is there any theory that predicts stability ranges? E.g. "one gas giant is stable for 2 G yr, but because of resonance issues, two gas giants are only stable for 2 M yr?" Or, " a system with a gas giant should eject planetismals out to stable Oort orbits in 100 M yr, but a system with ice giants will take 900 M yr to 'blenderize' the planetismals into dust."

Posted by: Gerald Jan 30 2016, 09:08 PM

I'm still trying to find out some hint to the age of KIC 8462852. There seems to be https://en.wikipedia.org/wiki/Gyrochronology, saying that fast-rotating sun-like stars are more likely to be young than slowly-rotating, more detail e.g. http://www.hcs.harvard.edu/~jus/0303/ing.pdf.
A rotation period of only 0.88 days would be a vague hint, that KIC 8462852 might be relatively young.
A second indicator of age is metallicity. It's estimated to be low for KIC 8462852 (0 +/- 0.1, the '-' doesn't make much sense). Another vague hint to not being too old (less than about half the main sequence lifetime). But data may be inaccurate.
A third indication is the mass. Since KIC 8462852 is assumed to be heavier (by a factor of 1.43, according to Wikipedia), its total lifetime should be shorter than that of the Sun.
More precise: The estimated main sequence lifetime for a 1.43 solar masses star is 10e10 x 1.43^(-2.5) years = 4.1e9 years, hence below the age of our solar system.

The radius of 1.58 solar radii, however, is larger than that of a https://en.wikipedia.org/wiki/Main_sequence#Sample_parameters of 1.43 solar masses , although this might partially be explained by some oblateness due to rapid rotation. But generally, stars leaving the main sequence towards giants are near the end of their lifetime.
Luminosity may be used as another indicator of age. Stars tend to brighten over time. But oblateness needs to be considered, when inferring the luminosity.


... regarding lifetimes of planetary systems, this has been investigated extensively. Roughly speaking it's more stable for very different orbital radii.
So I'd say an instability can be constructed after any given timespan.

Posted by: dudley Jan 31 2016, 12:53 AM

I believe the metallicity figure is compared to that of the Sun, which is set at zero. If so, KIC 8462852 is apparently thought to have the same metallicity as the Sun, plus or minus 10 percent.
I read that the typical rotation velocity of an F0 star is 95 km/sec. and an F5 star 25 km/sec. At 84 km/sec. KIC 8462852 (an F3 star) falls between these two.

Posted by: Gerald Jan 31 2016, 02:40 AM

https://en.wikipedia.org/wiki/Metallicity:

QUOTE
In astronomy and physical cosmology, the metallicity or Z is the fraction of mass of a star or other kind of astronomical object that is not in hydrogen (X) or helium (Y)

http://adsabs.harvard.edu/abs/2006CoAst.147...76A:
QUOTE
...The new solar abundances are lower than previously recommended values and the present solar metallicity, Z, and Z/X, decrease to Z = 0.0122 and Z/X = 0.0165 respectively ...

The 84 km/s is a little faster than average F3 as far as I understand http://assets.cambridge.org/97805217/72181/sample/9780521772181ws.pdf, e.g. fig 1.6:
QUOTE
Note, that the open cluster F dwarfs rotate more rapidly than their older, field counterparts.

The more likely interpretation would then be, that KIC 8462852 is considerably younger than 4.1 Gy.

Posted by: JRehling Feb 1 2016, 05:35 PM

Over the weekend, I downloaded the light curve data and started examining the various dips / dimming events. As noted in v2 (but not v1) of the "Where's the Flux?" paper, there are 10 events that are fairly significant in size (≥0.2%). As the biggest one is about 100x bigger than the smallest, the discussion has focused on the bigger dips, but all 10 are interesting.

What's odd is that the dips show different shapes, but are easily grouped into about four categories – three types that repeat three times each and do not look planetlike, and one that looks more planetlike, but is asymmetrical, and occurs once. I will probably organize my observations into a blog post, but some of the main points are:

1) The ones that appear similar are probably not, for the most part, repeat transits of single objects. They are similar in shape but very different in magnitude, and the triple occurrences are not spaced out evenly in time.

2) The types are:
T1) The single planetlike dimming event, which is very large.
T2) V-shaped dips, a shape which is in other systems indicative of star-star eclipses.
T3) A small peak followed by a brief brightening, then a larger peak. Interestingly, there are none in the opposite direction (large, then small). Two of these are very large.
T4) A symmetrical sequence of three subpeaks, with the largest one in the middle. This is not what you would see if a Saturn-like planet transited the Sun, but might see if a truly massive ring system transited a star. One of these is very large.

By "very large," I mean the maximum decrease in illumination is larger than could be explained by a planet more than twice the diameter of Jupiter.

The (T4) cases make me wonder if we're seeing something like the Jovian or Saturnian systems in a state of formation, with the respective satellite systems still like huge rings/toruses around the protoplanet. To show no IR excess might (my supposition) be explained if these systems are very far out. Perhaps some of the other types could be explained by various geometries. Then, the larger explanation would be that Tabby's star has a lot of giant protoplanet systems that are still evolving, with their Ganymedes, Titans, and Callistos, etc., still in the form of massive dust rings. What would need to be explained, still, is:

E1) Could this be consistent with the lack of IR excess if those systems are very far out? They still would be retransmitting the blocked light as longer-wavelength radiation, but perhaps at longer wavelengths than have yet been observed.

E2) Could one F dwarf star plausibly have so many giant planet systems? If we are witnessing ten of them transit in a span of four years, then the star would seemingly have a huge number of other ones that we didn't happen to observe. Is this plausible?

Fomalhaut has a dust ring at ~130 AU, but it emits a lot of IR, which indicates that Tabby's star is something different than a Fomalhaut system that simply happens to be seen edge-on.

Posted by: HSchirmer Feb 2 2016, 01:04 AM

QUOTE (JRehling @ Feb 1 2016, 06:35 PM) *
Could one F dwarf star plausibly have so many giant planet systems?
If we are witnessing ten of them transit in a span of four years, then the star would seemingly have a huge number of other ones that we didn't happen to observe. Is this plausible?


Recent papers suggest a family of obscuring objects, perhaps the result of a large disrupted KBO or centaur, would work. Think of Shoemaker Levy 9, beads on a string...



QUOTE
http://www.centauri-dreams.org/?p=34543
a paper from Eva Bodman and Alice Quillen (University of Rochester) titled “KIC 8462852: Transit of a Large Comet Family.” http://arxiv.org/abs/1511.08821

From the paper:
    …if the comet family model is correct, there is likely a planetary companion forming sungrazers. Since the comets are still tightly clustered within each dip, a disruption event likely occurred recently within orbit, like tidal disruption by the star.

From the abstract
    To reach a transit depth of about 0.2, the comets need to be in a close group of about 30 if around 100 km in radius or in a group of about 300 if around 10 km. The total number of comets required to fit all the dips is 73 around 100 km or 731 around 10 km comets. A single comet family from a large completely disrupted progenitor explains the last roughly 60 days of the unusual KIC 8462852 light curve


Another paper
It’s Lisse et al., “IRTF/SPEX Observations of the Unusual Kepler Lightcurve System KIC8462852,” now available
http://arxiv.org/abs/1512.00121
on the arXiv site. From the abstract, this interesting bit:
    Our results are inconsistent with large amounts of static close-in obscuring material or the unusual behavior of a YSO system, but are consistent with the favored episodic models of a Gyr old stellar system favored by Boyajian et al. (2015). We speculate that KIC8462852, like the ~1.4 Gyr old F2V system η Corvi (Wyatt et al. 2005, Chen et al. 2006, Lisse et al. 2012), is undergoing a Late Heavy Bombardment, but is only in its very early stages.

Posted by: Gerald Feb 2 2016, 12:01 PM

A LHB-like scenario, in this case caused by a recent disruption of a planet-like body sounds good in my ears, too.
The T4-type peaks might point towards a progressed re-accretion into ringed structures (think of https://en.wikipedia.org/wiki/Arp_147), while the T3-type peaks might be more similar to the cross section of an early instable kind of spiral arm of an accreting structure near the respective Roche limit (e.g. https://en.wikipedia.org/wiki/Arp_273), or to https://en.wikipedia.org/wiki/Antennae_Galaxies immediately after the collision of two clouds of debris.
(I've used galaxies as examples, since there is abundant material available, in contrast to interacting clouds of debris.)
A tidally disrupted or collided planet would also explain lack of a distinct IR structure, since the amount of freed gas and dust would be far less than in a Fomalhaut-like protoplanetary disc.
The T2-type might describe a cross-section of a cloud of debris with rapidly increasing density at the center (http://heritage.stsci.edu/2007/08/index.html).

Posted by: JRehling Feb 2 2016, 05:54 PM

QUOTE (HSchirmer @ Feb 1 2016, 06:04 PM) *
Recent papers suggest a family of obscuring objects, perhaps the result of a large disrupted KBO or centaur, would work.


That's a different hypothesis, and worth considering.

I note, however, that they are only trying to account for the last ~60 days, when many of the biggest events took place, and they're numbering the sub-dips of the dips as distinct events. I find it problematic for their model that the T4 types occur three times with the same shape. If separate, independent comets are causing all of those, then it's nine comets in 3 groups of 3 that just happen to have similar timing and relative magnitudes. That seems unlikely.

The similarity between the six, smaller, earlier dips and the last three (they call them seven, counting the sub-dips) needs an explanation, and they just don't discuss the earlier dips.

On a more general level, explanations include, but aren't limited to, these two sub-categories:

1) A little bit of occulting material that is close to the star but is on a long, elliptical orbit.
2) A lot of occulting material that is far from the star.

Both of these are problematic in different ways.

Posted by: JRehling Feb 2 2016, 07:08 PM

QUOTE (Gerald @ Feb 2 2016, 05:01 AM) *
(I've used galaxies as examples, since there is abundant material available, in contrast to interacting clouds of debris.)


Galaxies are a potentially useful analogue, since we have countless examples of them visible to a high degree of detail. However, they are only potentially useful – they universally have no single body which is an appreciable total of the sum mass or cross section, and that may or may not be true of Tabby's star's occulting objects.

Posted by: Gerald Feb 3 2016, 02:43 PM

Just checking, whether a cloud of debris can be made to fit with the observations.

Regarding the local behaviour of clouds of debris, I guess, eventually according simulations will be needed. The galaxies just provide some ideas.

Regarding the long-term dimming: Somewhat remotely, but might a ring of debris around an oblate (due to rotation) star precess, and that way gradually obscure the star? If so, can this happen in timescales of centuries?
Otherwise a rather homogenious cloud of gradually increasing optical density would need to be assumed, or some mechansim not immediately related to the debris.

Posted by: JRehling Feb 3 2016, 10:18 PM

Per your galaxy metaphor, Gerald, I wonder if something like the dust ring that surrounds the Sombrero Galaxy might be a useful model for Tabby's star explanations.

I would reiterate that we don't know if the century-long dimming was gradual or not. The data looks to me like the brightness may have dropped in two discrete steps. We'd need more data to know how gradual it was.

I think a dust cloud at long distances certainly can explain Tabby's star – but that doesn't mean it's the right explanation. It seems to me like a "super powerful" explanation – it could potentially explain any light curve, because the amount of and homogeneity of dust could provide arbitrarily many unconstrained variables.

The trio of three-peaked dimming events strikes me as a terribly important clue. That could happen by chance, but isn't very likely. So any hypothesis has to explain why those three-peaked events would occur frequently.

Posted by: Gerald Feb 4 2016, 01:07 PM

Yes, the Sombrero galaxy comes very close to a global ring system which, applied to Tabby's star, may partially obscure the central star.

The most advanced theoretical work I'm aware of is that of Eriguchi, e.g. http://adsabs.harvard.edu/full/1978PASJ...30..507E (1978), Fig. 7 on p.515, showing the transition between spheroid, concave hamburger to toroid figure of equilibrium for a differetially rotating polytrope, and Hachisu, with contributions of Miyama (1985): http://adsabs.harvard.edu/full/1985A%26A...143..355H, p.355ff, and http://articles.adsabs.harvard.edu//full/1985A%26A...147...13H/0000021.000.html, p13ff.
The latter paper mentions, that "probably these ring-like structures in the rotation dominant phase are dynamically unstable against fragmentation." Fig. 2 shows density profiles, including those of systems of rings.

Rotating polytropes aren't necessarily perfect approximations of clouds of debris, but they should be close to it.

Fragmentation leads to multiple systems. The fragments should behave somehow. I'd assume, that they should show features similar to the global system.
So we may again get local spheroids and rings, if undisturbed, or complex structures like for the collided galaxies, if two cloud fragments interact.

Ring(ed) systems should show up e.g. as triple (or higher-order) peaks when occulting a star.

Higher-order nesting might cause repeated triple peaks by the same ring system orbiting a larger body, or a multiple system the components orbiting each other, but due to the small Hill sphere of a "ringed moon" such structures are probably rather unstable.
About nested ring fragmentation, see e.g. http://articles.adsabs.harvard.edu/full/seri/ApJ../0224//0000497.000.html (1978), p.497ff.

For multiple system formation, see e.g. Figures 4 and 5 of http://adsabs.harvard.edu/full/1984A%26A...140..259H. p.262.

Assuming a moon rotating too rapidly to accrete all of its mass into its central body might work temporarily.
Another option for the repeated peak triples would be several local ringed systems of a similar size orbiting around the star, the similar size justified by symmetric fragmentation of a roughly symmetric (global) ring.

... so an explanations by occultations of some circumstellar disc may be able to find a theoretical basis, but only further observation can eventually decide...

Posted by: HSchirmer Feb 4 2016, 02:14 PM

QUOTE (Gerald @ Feb 4 2016, 02:07 PM) *
Another option for the repeated peak triples would be several local ringed systems of a similar size orbiting around the star, the similar size justified by symmetric fragmentation of a roughly symmetric (global) ring.


Or, could they be large moons around a gas giant?

Here's a quick thought experiment- what would our solar system look like under a LHB comet barrage?
There is some discussion that Ganymede and Callisto evolved differently because of LHB comet impacts-
http://www.planetary.org/blogs/emily-lakdawalla/2010/2363.html
Ok, if Jupiter's moons had multiple comet impacts, then wouldn't they have had transient rings? (eh, millions of years)

So, consider Jupiter during LHB, with a Saturn-sized ring 480k km, actually likely stop at Io's orbit (422k km).
But the other three Galilean moons orbit far enough apart, Europa at 6741k km, Ganymede at 1,070k km, and Callisto at 1,883K KM that they each might sport rings as wide as Saturn's main rings (about 300k km diameter)?

Posted by: Gerald Feb 4 2016, 02:44 PM

When taking Ganymede with a mass of about m=14.8e22 kg, and Jupiter with about M=1.9e27 kg, Ganymede orbital radius/semimajor axis a of about 1 million km, I get a https://en.wikipedia.org/wiki/Hill_sphere of r = a (m/3M)^{1/3}=30,000 km.
We'd need either much heavier moons, or the 10-fold distance from Jupiter to allow for a 300,000 km ring.
The ring would be well outside the Roche limit of the moon(s), hence probably unstable, unless sufficiently dilute. But stability isn't necessarily a requirement.

Posted by: HSchirmer Feb 4 2016, 03:04 PM

QUOTE (Gerald @ Feb 4 2016, 03:44 PM) *
When taking Ganymede with a mass of about m=14.8e22 kg, and Jupiter with about M=1.9e27 kg, Ganymede orbital radius/semimajor axis a of about 1 million km, I get a https://en.wikipedia.org/wiki/Hill_sphere of r = a (m/3M)^{1/3}=30,000 km.


Good point, more likely to be a big ring around Jupiter that has local lumps around the Galilean moons.
Then might see Jupiter with a Saturn-like ring, and the outer Galilean moons holding rings that are
eh, roughly the size (diameter) of Uranus or Neptune.

Well, that would create a rather wierd light curve...

Posted by: JRehling Feb 4 2016, 05:24 PM

The only way a large moon such as Ganymede could block a non-trivial amount of starlight for an F dwarf would be if a torus/ring in its orbit was made into a considerably opaque ring of impressive width. If Saturn, for example, transited Tabby's star, even if it were seen face-on, its ring system would hardly alter the light curve at all, as opposed to one large planet making a transit.

For the light curve to increase between the hypothesized ring and planet, the ring system would have to be very large. Note that the separation between Ganymede and Jupiter is only about half the diameter of Tabby's star. Callisto, Titan, and (especially) Iapetus would provide enough separation for the star to be seen un-obscured between the planet and the star. Meanwhile, Saturn itself is nowhere near big enough to create the maximum dips that we see, so they would have to be caused by a planet + ring combination that was very impressive itself.

I think if the Saturn system were pulverized, and it transited a star, we could get something very similar to Dip 9. But the devil's in the details – how many rings, what size, what optical depth?

Posted by: alan Feb 4 2016, 05:53 PM

Some articles that may be relevant

Iapetus's ridge from impact that led to the formation of a ring and a satellite:

http://adsabs.harvard.edu/abs/2011Icar..214..773L
http://adsabs.harvard.edu/abs/2012JGRE..117.3002D
http://adsabs.harvard.edu/abs/2012AGUFM.P21H..03K

Catastrophic impacts on the inner satellites of Saturn

http://adsabs.harvard.edu/abs/2015GeoRL..42..256M

Ring formation during the Late Heavy Bombardment:

http://adsabs.harvard.edu/abs/2009Icar..199..413C

Posted by: HSchirmer Feb 4 2016, 06:55 PM

QUOTE (JRehling @ Feb 4 2016, 05:24 PM) *
For the light curve to increase between the hypothesized ring and planet, the ring system would have to be very large. Note that the separation between Ganymede and Jupiter is only about half the diameter of Tabby's star. Callisto, Titan, and (especially) Iapetus would provide enough separation for the star to be seen un-obscured between the planet and the star. Meanwhile, Saturn itself is nowhere near big enough to create the maximum dips that we see, so they would have to be caused by a planet + ring combination that was very impressive itself.


Ever wake up just before dawn in early spring and walk around your lawn? The dew condensing on spiderwebs in the pre-dawn twilight reveals a topography of normally invisible spiderweb funnels and cones.


Is Tabby's Star is an example of "morning dew" where the movement of comet ice and dust reveals a spiderweb of gravity funnels and cones spun by planets and large moons? A flux of dust and grit revealing the invisible topography of gravity?

Until somebody gets, and (long pause) publishes spectra to figure out what exactly is blocking / absorbing / scattering the light from Tabby's star, then we're basically working backwards to figure out a mechanism that gets the most occultation out of the least amount material. E.g. circumstellar clouds, but more likely planetary rings, as a mass of material that is organized into rings has a better chance of getting the opacity and sharp-edged curves that are observed.

Let's see, Saturn's rings are the result of roughly one centaur's (250 km) mass of ice, 10^20 Kg. Tabby's star might have five earth masses of ice and dust to work with, that's, eh, 10^25 Kg. Estimates for our solar system are that roughly 5 earth masses of comets we pitched out to the far Oort cloud by our gas giants, Jupiter and Saturn. What if Tabby's star doesn't have a major league bullpen? What if they only have AAA pitching staff (ice giant)? Then, five eath masses worth of small comets fall back into the system. That's more than enough material to create those Kepler dips. With eh, one-hundred thousand times the mass of saturns' rings available to occult the star, it seems that there should be enough stuff to create those impressive dips that Kelper saw.

Consider a stately Copernican solar system of planets waltzing around the sun; then consider that it turns into a pachinko-pinball mosh pit. If a non-negligible portion of the system's mass is bouncing around and slamming into things, we can expect disruption, dust clouds and rings that create big dips in starlight.

Posted by: dudley Feb 8 2016, 07:42 PM

The scientific paper that first brought discussion of this star to the fore (Boyajian, et al. Where's the Flux?) contains an interesting, though little-remarked-upon observation. In section 2.1, The authors observe that the dips in light output seem to occur on multiples of periods of about 48 & 1/2 days.
In fact, there appear to be two groups of such dips, offset from one another by one half of the above period.
This might be taken to suggest a planet, comet, or compact debris cloud with an orbital period of ~ 24 days, except for the fact that most multiples of 24 days show no dips in brightness at all.
Any astrophysical explanation for the dimming of KIC 8462852 might be a better one, if it could explain how matter became arrayed in multiples of about 48 days, in an orbit around this star.

Posted by: Mongo Feb 9 2016, 03:27 PM

A http://www.wowsignalpodcast.com/2016/02/burst-11-dasch-photometry-with-dr-josh.html?m=1 with Dr. Josh Grindley of DASCH, about the reported long-term dimming of KIC 8462852.

Grindley is working on a paper about DASCH photometry of the star. In the podcast he destroys Hippke's criticism of Schaefer's paper, describing just how the methodology Hippke used was totally inadequate and inevitably produces incorrect results.

But he is also critical of Schaefer's methodology and results too. In fact, he looks at KIC 84628852 himself, using only the highest-quality data points with no warning flags attached, and finds a flat line -- no secular changes over the century of observations at all! So the observed long-term dimming would be an artifact caused by including doubtful observations.

If the erroneous observations at issue indicate a greater brightness than the correct level on average, and are more frequent the further back you go, then you would see a gradual dimming over time if they are included in the binned averages. But in reality the star's long-term brightness could be unchanged.

Posted by: dudley Feb 9 2016, 03:58 PM

Judging by Dr. Grindlay's own remarks, some of the 'flagged' images may have nothing seriously wrong with them, or at least nothing that would invalidate Dr. Schaefer's original findings. It would be well if we could hear from Dr. Schaefer, about the rationale he used in deciding to use, or not use certain 'flagged' images. It's already been established that he took some care to exclude certain problem images, which he believed would affect his results.

Posted by: beduino Mar 13 2016, 09:48 PM

I never really agreed that comets can block as much as 22% of a F-type star, so for the past few months I have been studying the possibility of KIC 8462852 being a long period binary, which as far as I can tell wasn't been ruled out by the original kic paper.
Here are some intriguing images.
http://imgur.com/a/6335i


Just for the record, this is my first post here on this site.

Posted by: HSchirmer May 5 2016, 05:15 PM

Well, it looks like there's another wierd long term eclipsing, err, something...

The newly discovered whatzit is TYC 2505-672-1, reported by astronomers at Vanderbilt.

Takes 69 years to orbit, and blocks out the star for about 3.5 years.


Posted by: Mongo May 24 2016, 09:09 PM

Bradley Schaefer comes out swinging: http://www.centauri-dreams.org/?p=35666

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

I recently received an email from Dr. Boyajian stating “I met with colleague Ben Montet, and he showed me his analysis of the Kepler Full Frame Images for KIC 846. It shows a pretty convincing dimming over the 4 yr time period (!!). He also shows that the dimming in our star is unique.” In a subsequent email, she stated “His method was pretty convincing, catching many things I wouldn’t have thought about. Doing this for a couple hundred other Kepler stars shows that the slope distribution is a Gaussian, and KIC 846 is an outlier.”

That is, in the 4.5 years of Kepler data, with a detailed analysis of the Full-Frame data, various known effects on the long-term light curves can be calibrated out, so a small amplitude overall fading can be recognized. 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.

http://www.centauri-dreams.org/wp-content/HippkeAnalysis.pdf

Posted by: Mongo Aug 5 2016, 03:46 PM

A new paper on arXiv supports the long-term dimming of this star: https://arxiv.org/abs/1608.01316

ABSTRACT

KIC 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ~1000 days, KIC 8462852 faded approximately linearly at a rate of 0.341 +/- 0.041 percent per year, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 yr. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, 0.6% change brightness at a rate as fast as 0.341 +/- 0.041 percent per year, and none exhibit either the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding while such a cloud could evade detection in sub-mm observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.

5.1. Comparison to DASCH Photometry

As mentioned in Section 1, Schaefer (2016) used 99 years of photometry from the DASCH project to analyze the behavior of KIC 8462852, finding a decrease in brightness of 14% from 1890 to 1989. Hippke et al. (2016) performed an independent analysis of the DASCH photometry, confirming that the photographic data yield a fainter magnitude for KIC 8462852 in the late 20th century compared to the end of the 19th century. However, Hippke et al. argue that the DASCH measurements from 1890 to 1952 are best described by a constant brightness and measurements from 1967 to 1989 are best described by a different (fainter) constant brightness, with systematic errors accounting for the offset.

We attempt to reproduce both results (for KIC 8462852 only, not the comparison stars). We find that either a linear decline in brightness with time or a constant brightness with a systematic offset between pre-1952 and post-1967 observations is a reasonable description of the DASCH measurements. The unfortunate gap of 15 years with very few observations in the middle of the century makes it difficult to distinguish between the two models. Which explanation to prefer then depends on one’s assessment of whether a star steadily fading for a century or a change in the photometric calibration of the Harvard plates around 1962 is more likely (or less unlikely). The fading that we detect from 2009 to 2013 with the Kepler FFI images does not necessarily represent a confirmation that KIC 8462852 also dimmed over the preceding 129 yr, but could make that interpretation of the DASCH data more plausible.

Posted by: JRehling Aug 14 2016, 04:26 AM

I'm a neophyte in studying deep space astrophysics, but I recently learned of something that reminds me – but maybe no one else – of Tabby's Star. This is Hubble's Variable Nebula (NGC 2261). As the nickname implies, this nebula varies in brightness (by 2 magnitudes, a factor of ~6), on a time scale of days, which is particularly interesting given that it is about 1 light year in radius, which would – one might think – cause variations in the central star's brightness to spread out across the nebula and average out. What is seen is, fascinatingly, superluminal motion, as the patterns of illuminated areas spread outward faster than the speed of light. It seems apparent that the variation in illumination from the central star is direction-specific, so that patterns of light and dark move through/across the nebula as those radial variations take place. A suggestive possible analogue is someone holding a flashlight surrounded by sheets of gauze, making patterns move at a distance across the gauze as they turn the flashlight.

Undoubtedly, Tabby's Star and NGC 2261 have some things in common, but whether those things are superficial or meaningfully related is another matter. I haven't seen anyone suggest a relationship between them, and NGC 2261 is itself mysterious in nature, although some plausible guesses as to its nature exist. What's interesting about using NGC 2261 as a starting point is that we can resolve the nebula pretty well, whereas Tabby's Star has only been amenable to photometry.

Some facts and rather fascinating animations of NGC 2261 are here:
http://www.floch5.com/ds99/ngc2261.htm

Posted by: HSchirmer Oct 7 2016, 04:12 PM

QUOTE (JRehling @ Aug 14 2016, 04:26 AM) *
Undoubtedly, Tabby's Star and NGC 2261 have some things in common, but whether those things are superficial or meaningfully related is another matter. I haven't seen anyone suggest a relationship between them, and NGC 2261 is itself mysterious in nature, although some plausible guesses as to its nature exist. What's interesting about using NGC 2261 as a starting point is that we can resolve the nebula pretty well, whereas Tabby's Star has only been amenable to photometry.


Another superficial, but related idea- close encounters between centaurs (minor planets) and gas giants result in centaurs with rings.

http://aasnova.org/2016/09/02/rings-from-close-encounters/
"In these cases the icy mantle and even some of the centaur’s core can be ripped away and scattered,
becoming gravitationally bound to the largest remaining clump of the core.
The particles travel in highly eccentric orbits, gradually damping as they collide with each other
and forming a disk around the remaining core. "


Interesting, generally when you think Nice model and planets, you think of comets bombarding planets,
hadn't thought of 40,000 minor planets developing ice-grain rings.

Posted by: Holder of the Two Leashes Dec 22 2016, 02:05 PM

A new theory about the star, the irregular dimmings might be intrinsic to the star itself:

http://phys.org/news/2016-12-avalanche-statistics-tabby-star-phase.html

Posted by: HSchirmer May 19 2017, 07:56 PM

LOOK NOW...

Star is dimming NOW.

If you've got a telescope, point it ASAP.

Posted by: JRehling May 19 2017, 10:03 PM

I took a picture of it a few months ago, and I could take another picture now with the same camera parameters and compare the difference. That'd make for a nice blink GIF. It will have to be a pretty big dimming event to be noticeable, though, and to exceed differences in seeing conditions, etc.

Posted by: Xcalibrator May 21 2017, 12:09 AM

http://www.wherestheflux.com/single-post/2017/05/19/WTF-Has-Gone-Into-a-Dip, although it's not updated very often--latest was May 19 with the announcement and a plot of photometry showing 2.5% dip so far. There's a bit more chatter on https://twitter.com/boyajiansstar?lang=en with some APO (Apache Point Obs?) spectra; I'm not sure how to interpret it. Optical spectra experts care to comment?

Posted by: JRehling May 21 2017, 06:17 PM

By the way, at the same time and almost the same part of the sky, there is, coincidentally, a supernova currently visible in galaxy NGC 6946, and it's very convenient to see both of these episodes in one session.

The spectral analysis of this dimming event may likely resolve the nature of the mystery, if any thermal/compositional signatures are seen – or aren't. I'd place my wager on material in the interstellar medium coincidentally between us and the star, but the endogenous explanations (or lack of explanation… this would seem to be a never-before seen phenomenon) make a good case, too.

Posted by: HSchirmer May 23 2017, 01:11 AM

QUOTE (JRehling @ May 21 2017, 06:17 PM) *
this would seem to be a never-before seen phenomenon


Synestia, a New Type of Planetary Object

Well, here's an interesting new idea - smack two planets together, you get a gravitationally bound
collision remnant, which is roughly an order of magnitude larger than the initial planet(s).

https://www.ucdavis.edu/news/synestia-new-type-planetary-object

http://onlinelibrary.wiley.com/doi/10.1002/2016JE005239/abstract

So, two Jovian size planets collide, the resulting Synestia might be big enough to cause a 20% occultation.
That form could last for several centuries if the energy and angular momentum are high enough

 

Posted by: HSchirmer May 23 2017, 01:43 AM

QUOTE (JRehling @ May 21 2017, 06:17 PM) *
The spectral analysis of this dimming event may likely resolve the nature of the mystery, if any thermal/compositional signatures are seen – or aren't.


Looks like "aren't" at least initially...

QUOTE (http://www.astronomerstelegram.org/?read=10406)
We report medium resolution spectroscopy (R=2500) taken with the FRODOSpec fibre fed integral field spectrograph of the 2.0 meter Liverpool Telescope, La Palma obtained on 20th May 2017 starting at 01:20UT. Three 600 second exposures were obtained, giving a total integration time of 1800 seconds. The wavelength range was 5800 - 9400 Angstroms.
...
In an initial analysis we find no difference between the two spectra...



 

Posted by: HSchirmer May 23 2017, 03:36 AM

QUOTE (Holder of the Two Leashes @ Dec 22 2016, 02:05 PM) *
A new theory about the star, the irregular dimmings might be intrinsic to the star itself:


Well, on the other hand, the recent 3% dip MIGHT indicate that the pattern with the 22% dip is repeating.
If so, then this is VERY interesting for 2 reasons.

First, we actually get to analyze the dips as they happen, with spectra.
Second, this would place whatever-is-causing-the-dips roughly within the goldilocks zone of the star

 

Posted by: HSchirmer May 23 2017, 05:39 AM

QUOTE (HSchirmer @ May 23 2017, 03:36 AM) *
Well, on the other hand, the recent 3% dip MIGHT indicate that the pattern with the 22% dip is repeating.
If so, then this is VERY interesting for 2 reasons.

First, we actually get to analyze the dips as they happen, with spectra.
Second, this would place whatever-is-causing-the-dips roughly within the goldilocks zone of the star


Oh, wow... a third point...
https://twitter.com/david_kipping/status/866127740776456192
These dips last for days.
If this is something with a 750 day circular orbit, then each day of occultation represents an arc 700,000km long.
Then the recent 3% dip over 2.5 days requires something opaque that is
roughly 5 sun (sol) diameters in length, and perhaps 2 Jupiters wide,
moving between Tabby's Star and us. If it's not completely opaque, then it's got to be even bigger.

Wow, that's big.

Posted by: alan May 24 2017, 07:12 PM

KIC 8462852: Will the Trojans return in 2021?

QUOTE
We aim at offering a relatively natural solution, invoking only phenomena that have been previously observed, although perhaps in larger or more massive versions. We model the system using a large, ringed body whose transit produces the first dimming and a swarm of Trojan objects sharing its orbit that causes the second period of multiple dimmings. The resulting orbital period is T≈12 years, with a semi-major axis a≈6 au. In this context the recent observation of a minor dimming can be explained as a secondary eclipse produced by the passage of the planet behind the star. Our model allows us to make two straightforward predictions: we expect the passage of a new swarm of Trojans in front of the star starting during the early months of 2021, and a new transit of the main object during the first half of 2023.


https://arxiv.org/abs/1705.08427

Posted by: HSchirmer May 24 2017, 11:56 PM

QUOTE (alan @ May 24 2017, 07:12 PM) *
KIC 8462852: Will the Trojans return in 2021?

https://arxiv.org/abs/1705.08427


Good paper, great graphics.

They're proposing a mega-saturn, with rings that reflect 3% of the starlight back at us as it transits in 3 days.
At 6AU, [edit] not sure that a 3 day transit fits with the orbital velocity or ring size.

[revised the calculations..]
The area of Tabby's Star that we can see is basically a circle.
The star is listed as being about 1.5 solar radii across, (radius of sun is ~700,000 km)
Consider the area of a circle is ¶r^2 so 1.5 radius =~7 area in srs (sol radii squared)

To reflect 3% more light, you need at minimum, 3% more surface area for the rings,
And 3% of 7 gives 0.21 srs in area. Divide by ¶ gives .067, take square root gives .25 as radius, or 180,000 km.
That's workable, Saturn's rings go to eh, 80,000 km, so it's a bigger version of something we've seen.
[edit] and it's within observed J1407 "super saturn" with rings 90,000,000 km in radius.

Main question for that, is whether the planet and rings that size would transit the star in 3 days.
Orbiting at 6AU, distance around the orbit would be ¶ x diameter or 12¶AU traveled over 12 years.
[edited to add the correct number of zeros]
Each year it travels ¶AU, or 3.14 x 150,000,000 km or 471,000,000 km.
Over 365 days, that's 1,290,000 km per day, over the 3 days of the transit,
the planet moves 3,870,000 km.

So, at 6AU, you need rings almost 3,870,000 km across to cause a 3 day event.

Posted by: hendric May 25 2017, 04:56 PM

1 AU is 150,000,000 km, not 150,000.

Posted by: HSchirmer May 25 2017, 05:33 PM

QUOTE (hendric @ May 25 2017, 04:56 PM) *
1 AU is 150,000,000 km, not 150,000.


Sorry about that, went back and added the correct number of 000s.


Actually, this proposal is rather similar to J1407, the "super saturn".
That's a planet with rings 90,000,000 km in radius, orbit of 4-14 years, and a 56 day transit.

Posted by: dudley May 26 2017, 04:15 PM

This new hypothesis calls for a planet about 30 percent the size of KIC 8462852, exclusive of the rings, so much larger than Jupiter. Isn't it thought that planets don't grow much larger than Jupiter, but merely become denser, compressed by their own gravity?
Then, too, an object on this scale would fuse hydrogen at its core, wouldn't it? That would make for a conspicuous second star in the Boyajian's Star system. Such a star has not been reported.

Posted by: HSchirmer May 26 2017, 10:34 PM

QUOTE (dudley @ May 26 2017, 05:15 PM) *
This new hypothesis calls for a planet about 30 percent the size of KIC 8462852, exclusive of the rings, so much larger than Jupiter. Isn't it thought that planets don't grow much larger than Jupiter, but merely become denser, compressed by their own gravity?
Then, too, an object on this scale would fuse hydrogen at its core, wouldn't it? That would make for a conspicuous second star in the Boyajian's Star system. Such a star has not been reported.


Here's an interesting theory - good attempts to combine explanation of long term dimming AND mega transits.

What if Tabby's star is slowly dimming because it ate a Jovian sized planet about a thousand years ago?
What if Tabby's star is obscured by the Jovian icy moons which are now short period mega comets?

System appears to have a distant companion star, which could pull gas giants into elliptical orbits.
Models suggest that a Jovian size planet forced into an elliptical orbit will end up stripped of it's large icy moons.
The moons go into short period comet style orbits, i.e. imagine Europa, Ganymede, Callisto as sun grazing comets.
Those icy moons would produce massive outgassing and massive dips in brightness.
The Jovian planet ends up disrupted and digested, the star's brightness peaks due to a dump of gravitational energy.
You get a slow dimming as the star returns to normal brightness over hundreds or thousands of years.

QUOTE (https://www.youtube.com/watch?v=risNfZxz6DQ)
Cool Worlds video by Brian Metzger and Nick Stone on their hypothesis for Tabby's Star behaviour

Posted by: ngunn May 27 2017, 09:26 AM

For me that's the first suggestion that sounds really plausible. In their video they mention that a possible argument against is the issue of frequency, in other words that the presumed rarity and short-lived nature of such an event makes it very unlikely that one would have been observed. I don't see that as much of a problem given the uncertainties involved and the fact that this is (so far) a unique example.

They consider also in the video the likely effects of a star swallowing anything ranging from Moon-sized to Jupiter-sized, but why stop there? How about Trappist-1-sized? That recent discovery, though also unique so far, must be upping our estimates of the prevalence of very compact systems available for disruption by stellar companions.

Posted by: HSchirmer May 27 2017, 10:27 AM

QUOTE (ngunn @ May 27 2017, 10:26 AM) *
They consider also in the video the likely effects of a star swallowing anything ranging from Moon-sized to Jupiter-sized, but why stop there? How about Trappist-1-sized?


Yep, that could happen.
I think the emphasis is more about a gas-giant that forms at the snowline, and ends up eccentric,
which isn't uncommon, e.g. https://arxiv.org/ftp/arxiv/papers/1205/1205.2429.pdf

because you'd also expect exo-Galilean moons (e.g. icy bodies which would otherwise qualify as dwarf planets)
which remain after the planet is gone, but end up on short period comet style orbits,
so the 3% and 20% dips result from truly giant comets. (Giant as in a nucleus the size of Mars)

Think of an orbit something like HD 80606b
e.g. http://www.space.com/6364-exoplanet-sees-extreme-heat-waves.html
but an ice-ball might have a freeze-thaw water atmosphere, and perhaps a freeze-thaw ocean...

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