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KIC 8462852 Observations
JRehling
post Oct 15 2015, 04:45 PM
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Kepler found one very, very strange case:

http://www.theatlantic.com/science/archive...-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.
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ZLD
post Oct 15 2015, 08:42 PM
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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!


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scalbers
post Oct 15 2015, 10:08 PM
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Could this be like some of the dense clouds that eclipse Epsilon Aurigae on occasion?


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ngunn
post Oct 15 2015, 10:09 PM
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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.
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JRehling
post Oct 15 2015, 10:29 PM
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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
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ZLD
post Oct 16 2015, 12:26 AM
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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.


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JRehling
post Oct 16 2015, 04:27 AM
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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.
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nprev
post Oct 16 2015, 04:44 AM
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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...?


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ZLD
post Oct 16 2015, 05:28 AM
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@JReling: Thanks for the correction. I skimmed it earlier and thought I understood differently.


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silylene
post Oct 16 2015, 02:43 PM
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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.
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JRehling
post Oct 16 2015, 04:10 PM
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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.
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JRehling
post Oct 16 2015, 04:27 PM
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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.
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HSchirmer
post Oct 17 2015, 12:41 PM
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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?
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scalbers
post Oct 17 2015, 01:17 PM
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Here's a web page that helps explain Epsilon Aurigae that might have some parallels as suggested earlier:

http://www.daviddarling.info/encyclopedia/...on_Aurigae.html


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ngunn
post Oct 17 2015, 08:54 PM
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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.
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