KIC 8462852 Observations Options

[HSchirmer]

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 comet storms in other star systems that result in big hits on inner solar system planets.

That system, 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.

[JRehling]

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.

[HSchirmer]

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 Did Saturn's rings form during the Late Heavy Bombardment ? 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.

[stevesliva]

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.

[Gerald]

...
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 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.

[Gerald]

... 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 variable stars, caused by several kinds of oscillations.
Some variable stars show intrinsic variability which doesn't follow a regular pattern.
Superposition of several oscillations might look chaotic.

[HSchirmer]

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 prior thread post about mega rings 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.

Gigantic ring system around J1407b much larger, heavier than Saturn’s
http://www.rochester.edu/newscenter/gigant...m-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 Crashing comets make rings ripple 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.

[dudley]

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.

[JRehling]

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.

[stevesliva]

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?

[Hungry4info]

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

[Explorer1]

So the modern dimming is just comets after all?

[silylene]

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.

[dudley]

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.

[JRehling]

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.