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KIC 8462852 Observations
HSchirmer
post May 23 2017, 05:39 AM
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QUOTE (HSchirmer @ May 23 2017, 03:36 AM) *
Well, on the other hand, the recent 3% dip MIGHT indicate that the pattern with the 22% dip is repeating.
If so, then this is VERY interesting for 2 reasons.

First, we actually get to analyze the dips as they happen, with spectra.
Second, this would place whatever-is-causing-the-dips roughly within the goldilocks zone of the star


Oh, wow... a third point...
https://twitter.com/david_kipping/status/866127740776456192
These dips last for days.
If this is something with a 750 day circular orbit, then each day of occultation represents an arc 700,000km long.
Then the recent 3% dip over 2.5 days requires something opaque that is
roughly 5 sun (sol) diameters in length, and perhaps 2 Jupiters wide,
moving between Tabby's Star and us. If it's not completely opaque, then it's got to be even bigger.

Wow, that's big.
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alan
post May 24 2017, 07:12 PM
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KIC 8462852: Will the Trojans return in 2021?

QUOTE
We aim at offering a relatively natural solution, invoking only phenomena that have been previously observed, although perhaps in larger or more massive versions. We model the system using a large, ringed body whose transit produces the first dimming and a swarm of Trojan objects sharing its orbit that causes the second period of multiple dimmings. The resulting orbital period is T≈12 years, with a semi-major axis a≈6 au. In this context the recent observation of a minor dimming can be explained as a secondary eclipse produced by the passage of the planet behind the star. Our model allows us to make two straightforward predictions: we expect the passage of a new swarm of Trojans in front of the star starting during the early months of 2021, and a new transit of the main object during the first half of 2023.


https://arxiv.org/abs/1705.08427
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HSchirmer
post May 24 2017, 11:56 PM
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QUOTE (alan @ May 24 2017, 07:12 PM) *
KIC 8462852: Will the Trojans return in 2021?

https://arxiv.org/abs/1705.08427


Good paper, great graphics.

They're proposing a mega-saturn, with rings that reflect 3% of the starlight back at us as it transits in 3 days.
At 6AU, [edit] not sure that a 3 day transit fits with the orbital velocity or ring size.

[revised the calculations..]
The area of Tabby's Star that we can see is basically a circle.
The star is listed as being about 1.5 solar radii across, (radius of sun is ~700,000 km)
Consider the area of a circle is r^2 so 1.5 radius =~7 area in srs (sol radii squared)

To reflect 3% more light, you need at minimum, 3% more surface area for the rings,
And 3% of 7 gives 0.21 srs in area. Divide by gives .067, take square root gives .25 as radius, or 180,000 km.
That's workable, Saturn's rings go to eh, 80,000 km, so it's a bigger version of something we've seen.
[edit] and it's within observed J1407 "super saturn" with rings 90,000,000 km in radius.

Main question for that, is whether the planet and rings that size would transit the star in 3 days.
Orbiting at 6AU, distance around the orbit would be x diameter or 12AU traveled over 12 years.
[edited to add the correct number of zeros]
Each year it travels AU, or 3.14 x 150,000,000 km or 471,000,000 km.
Over 365 days, that's 1,290,000 km per day, over the 3 days of the transit,
the planet moves 3,870,000 km.

So, at 6AU, you need rings almost 3,870,000 km across to cause a 3 day event.
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hendric
post Yesterday, 04:56 PM
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1 AU is 150,000,000 km, not 150,000.


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HSchirmer
post Yesterday, 05:33 PM
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QUOTE (hendric @ May 25 2017, 04:56 PM) *
1 AU is 150,000,000 km, not 150,000.


Sorry about that, went back and added the correct number of 000s.


Actually, this proposal is rather similar to J1407, the "super saturn".
That's a planet with rings 90,000,000 km in radius, orbit of 4-14 years, and a 56 day transit.
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