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KIC 8462852 Observations
HSchirmer
post Oct 21 2015, 05:30 PM
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QUOTE (Mongo @ Oct 21 2015, 04:35 PM) *
But the planet transits the star


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

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


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

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

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

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


Well, as I speculated above, what about a binary gas giant, both with rings.
That would naturally create mulitple occulting objects in the same plane.
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Explorer1
post Oct 21 2015, 05:43 PM
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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
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silylene
post Oct 21 2015, 06:57 PM
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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.
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alan
post Oct 21 2015, 07:33 PM
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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.
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JRehling
post Oct 22 2015, 12:40 AM
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QUOTE (silylene @ Oct 21 2015, 11:57 AM) *
Yes this star would require 3 super-Saturns with the ring planes titled at high angles to the ecliptic. Agreed. Unlikely? Yes. But then we have Uranus and Pluto-Charon. For the sun, 25% of the large planets have a highly inclined orientation.


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

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

If we see five of these coincidences in one system, we ought to be seeing two or three of them in orders of magnitudes more systems, and we aren't.
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AndyG
post Oct 22 2015, 08:37 AM
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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
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JRehling
post Oct 22 2015, 08:54 AM
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QUOTE (AndyG @ Oct 22 2015, 01:37 AM) *
Huge, dense and opaque ring systems that are tilted during a transit: wouldn't there be a noticeable slight rise in apparent stellar brightness when this planet was near the star, half a year later?


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

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

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

Explanations that would not produce a surge – if the clouds of occluding material were of low albedo, or quite far from the star, such as in another star system which is coincidentally aligned.
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HSchirmer
post Oct 23 2015, 12:33 PM
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QUOTE (JRehling @ Oct 22 2015, 12:40 AM) *
If we see five of these coincidences in one system, we ought to be seeing two or three of them in orders of magnitudes more systems, and we aren't.



Something just occurred to me

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

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


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...
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Hungry4info
post Oct 23 2015, 01:10 PM
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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.


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-- Hungry4info (Sirius_Alpha)
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Explorer1
post Oct 31 2015, 02:17 AM
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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
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Hungry4info
post Oct 31 2015, 04:27 AM
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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.


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Explorer1
post Oct 31 2015, 06:52 AM
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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.
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JRehling
post Nov 2 2015, 05:01 PM
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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.
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HSchirmer
post Nov 3 2015, 03:44 AM
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QUOTE (JRehling @ Nov 2 2015, 05:01 PM) *
...I can't think of many processes that would discard iron and keep the heavier stuff.
... I think the absolute maximum for any extrasolar planets would be around that level or less.


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

So, is there an inverse of the Chandrashekar limit, that requires small pieces of electron degenerate matter revert to "ordinary" matter below a specific mass? I recall theories about chunks of material made with charmed or strange quark properties remaining stable once formed
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JRehling
post Nov 3 2015, 04:20 PM
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QUOTE (HSchirmer @ Nov 2 2015, 08:44 PM) *
Well, what about a white dwarf that hits something and goes splat.


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