KIC 8462852 Observations Options

[JRehling]

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.

[ZLD]

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!

[scalbers]

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

[ngunn]

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.

[JRehling]

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

[ZLD]

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.

[JRehling]

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.

[nprev]

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...?

[ZLD]

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

[silylene]

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.

[JRehling]

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.

[JRehling]

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.

[HSchirmer]

...
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?

[scalbers]

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

[ngunn]

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.

[HSchirmer]

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 V1581 Cygni 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.

[JRehling]

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.

[ngunn]

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.

[HSchirmer]

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.

[Hungry4info]

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

[JRehling]

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.

[JRehling]

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.

[HSchirmer]

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.

[Rittmann]

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-...er-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.

[ngunn]

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

[silylene]

.....
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.

[JRehling]

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.

[Explorer1]

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.

[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.
...

Actually, that might fit.


Binary Saturns.

Penn State has some good discussion
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.

[Mongo]

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.

[HSchirmer]

But the planet transits the star

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

, 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.

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.

[Explorer1]

And now a star getting 40% of its light blocked: http://www.cbc.ca/news/technology/white-dw...eroid-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/...ature15527.html

[silylene]

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.

[alan]

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 Jupiter trojans 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.

[JRehling]

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.

[AndyG]

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

[JRehling]

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.

[HSchirmer]

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


After two small dips in 2009, which had attracted the notice of the Planet Hunters, there was another major dip of about 15 percent in 2011, and it lasted nearly a week. Finally, there was a whole series of dips in 2013, one of them managing to dim the star’s light by 22 percent.

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...

[Hungry4info]

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.

[Explorer1]

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/c...ONFIRMED_PLANET

[Hungry4info]

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.

[Explorer1]

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.

[JRehling]

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.

[HSchirmer]

...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

[JRehling]

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.

[HSchirmer]

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.

[JRehling]

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.

[Hungry4info]

Besides, we know of numerous pulsar+WD binaries.

[nprev]

JRehling is correct. Please stay on topic.

[ZLD]

JPL posted a short article yesterday further suggesting the comet swarm hypothesis for the strange occurrence with KIC 8462852. The referenced paper is here 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.

[Mongo]

Paper is up on ARXIV now:

KIC 8462852 - The Infrared Flux

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.

[Mongo]

KIC 8462852 Faded at an Average Rate of 0.165+-0.013 Magnitudes Per Century From 1890 To 1989

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%!

[nprev]

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.

[Mongo]

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 IRTF/SPEX Observations of the Unusual Kepler LightcurveSystem KIC8462852:

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.

[nprev]

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

[ZLD]

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.

[Gerald]

Black holes (besides hypothesized primordial ones) have a minimum mass a few (1.5 to 3) solar masses, since they form by overcoming the Chandrasekhar mass limit for neutron stars (Tolman–Oppenheimer–Volkoff 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.

[JRehling]

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.

[Mongo]

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

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 suffering 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 this podcast 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.

[Mongo]

Okay, I've decided to download the full archive of Harvard Observatory observations of this object. I went to the DASCH Lightcurve Access 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.

[Mongo]

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.

Attached thumbnail(s)

 

[dudley]

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.

[nprev]

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.

[HSchirmer]

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?

[JRehling]

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.

[HSchirmer]

...
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....

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.

[dudley]

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.

[JRehling]

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.

[JRehling]

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.

[HSchirmer]

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.

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.

[dudley]

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?

[JRehling]

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.

[JRehling]

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.

[HSchirmer]

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.

The dip at D1500 is then interpreted as the same material seen one orbit later,
with the 750 day period implying an orbit at 1.6 AU.
...
A more robust prediction is that future dimming events should occur roughly every 750 days,
with one in 2015 April and another in 2017 May.
..,.
Thus, while this scenario is attractive because it is predictive, the periodicity argument may be inconsistent, and the probability of witnessing such an event may be very low
...

Likewise, if the two deep dipping events at D800 and D1500 are from the same orbiting body (or bodies), a
period of 700 – 800 days remains a possibility.
...

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

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-

A broad range of scenarios for the dipping behavior that involve occultation by circumstellar dust clumps was considered. Among these, we find that the break-up of one or more massive exocomets (or planetesimals on comet-like orbits) provides the most compelling explanation consistent with the data in hand.
The required mass of the original body may have been in excess of 3×10^21 grams (only 0.3% the mass of Ceres, and perhaps 100 km in diameter).

It's not that hard to conceptualize an area where several 100 km objects orbit, we call it the asteroid belt. 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

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 Oort cloud is estimated to have about 5 earth masses worth of comets, divided into trillions of bodies, with several billion 20km or larger. 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 "Kessler catastrophe" solar system?

[dudley]

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.

[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.

[Hungry4info]

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

[JRehling]

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.

[Gerald]

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 Bok globule 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 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.

[JRehling]

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

https://www.reddit.com/r/IAmA/comments/3set...sts_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.

[JRehling]

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/2015/10/1...heres-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."

[dvandorn]

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.

[Gerald]

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 AstroWright)

Other ideas would be bandwidth-limited pulses similar to a sinc pulse 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 Feigenbaum-ish bifurcation 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.

[JRehling]

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.

[Gerald]

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.

[dudley]

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.