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KIC 8462852 Observations
HSchirmer
post Oct 18 2015, 12:07 PM
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QUOTE (ngunn @ Oct 17 2015, 08:54 PM) *
Accepting the idea of eclipsing objects of some kind, why do they have to be in orbit around the star?
Couldn't they be anywhere in the line of sight?


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

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


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

Second, turns out that there is a nearby (~14 LY) triple star system 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.
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JRehling
post Oct 19 2015, 08:12 PM
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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.
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ngunn
post Oct 19 2015, 09:19 PM
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QUOTE (JRehling @ Oct 19 2015, 09:12 PM) *
It's the second objection that seems thorniest: How can the closer system have so many objects that transit the more distant star? It would require either that the closer system have a dense halo of large objects or that the closer system has a lot of large objects orbiting in the same plane that coincidentally contains the farther star.


I've been thinking about this too. To observe eclipses in a single system you need one coincidence: The plane of the system must be aligned with us. For a nearer system to produce multiple eclipses of a more distant star you need two coincidences. The nearer sustem must be edge on to us as in the ordinary case, but in addition its proper motion relative to the background star must be in the same direction also to carry the whole succession of objects across the star from our viewpoint. If the nearer system is fairly compact, almost like Galilean moons around a brown dwarf for example, that may not be too much to ask. I agree with you it's difficult to call the relative improbability of this versus a single system scenario. It's clearly something improbable or we would be seeing more of them! For the moment, though, I'm noticing a sequence of events that happens only once and a degree of obscuration that suggests to me that the eclipsing objects are much closer than the star.
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HSchirmer
post Oct 19 2015, 09:26 PM
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QUOTE (JRehling @ Oct 19 2015, 09:12 PM) *
I don't know. Something weird is happening.
The closer-and-farther system case seems to handle one weird aspect of the data – the size of the objects – but adds another weird thing – the coincidental perfect alignment – and maintains several of the weird things from the single-system hypothesis.
I don't know which, if either, of those two explanations is more likely.


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

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

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

So, how certain are we about the WTF star? IRC, the classification is F-type, 6k-7k kelvin, located about 1,400 LY away.
Ok, what if it's not a "normal" distant F star, but a variant of procyon, (F star and white dwarf) but with a white dwarf that has a 6k-7k temperature. So, what would a near by white dwarf pulling material from a brown dwarf look like? Could it be something with the temperature and H2 lines that resemble a F class star? The luminous star would be roughly earth sized, and thus the observed occultations could be a result of "standard" rocky planets or dwarf planets.
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Hungry4info
post Oct 20 2015, 12:48 AM
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Look at the light curve. A dark sphere transiting a luminous sphere doesn't fit the data well.


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-- Hungry4info (Sirius_Alpha)
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JRehling
post Oct 20 2015, 02:09 AM
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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.
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JRehling
post Oct 20 2015, 05:46 PM
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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.
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HSchirmer
post Oct 20 2015, 06:50 PM
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QUOTE (JRehling @ Oct 20 2015, 06:46 PM) *
Another thought: A comet seen transiting its star would be, most likely, pointing its tail directly away from the star and directly towards us. This would reduce its size, but increase its opacity. We have never observed a comet in this solar system from that geometry.

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


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

Shoemaker Levy's beads-on-a-string appearance comes to mind.
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Rittmann
post Oct 20 2015, 08:49 PM
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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.
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ngunn
post Oct 20 2015, 09:54 PM
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I'm still not buying the comets idea, sorry.
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silylene
post Oct 21 2015, 03:33 PM
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QUOTE (JRehling @ Oct 16 2015, 05:27 PM) *
.....
And that scenario with rings that we see face-on from Earth would be provided only if the rings were perpendicular to the planet's orbit, which is unlikely to occur by chance; any deviation from that geometry would require a still larger ring system to provide the observed darkening.

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


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

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

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

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

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

I would like to understand better the long-term stability of large ringed systems in a complex solar system with several large planets and their gravitational interactions. I do suspect that one could have several "super-Saturns" and this would be a stable system.
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JRehling
post Oct 21 2015, 04:04 PM
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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.
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Explorer1
post Oct 21 2015, 04:13 PM
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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.
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HSchirmer
post Oct 21 2015, 04:31 PM
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QUOTE (silylene @ Oct 21 2015, 03:33 PM) *
Yes, I am proposing a complicated planetary system with multiple planets with giant ringed systems (at least 3 were observed), plus some planets without ringed systems for the minor occultations, and perhaps even additional exomoons, because if you look closely at the data, there are some shoulder spikes.
...


Actually, that might fit.


Binary Saturns.

Penn State has 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.
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Mongo
post Oct 21 2015, 04:35 PM
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QUOTE (Explorer1 @ Oct 21 2015, 04:13 PM) *
But as long as the parent planet's spin axis is pointed towards us, wouldn't the rings be perpendicular through the entire orbit? Uranus doesn't seem like a good example considering it orbits the sun, and its axis is pointed at us only twice each time.
Here's how I'm imagining it: point a finger at something far away, and then move your arm in a circle in front of you. The finger is the spin axis, the hand is the planet and rings, and the circle is the orbit.


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

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