Author Topic: Boyajians Star Updates And Discussion  (Read 295834 times)

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #320 on: 05/23/2017 06:23 am »
Glad he posted this considering the public interest in the topic.

Quote
Jason Wright @Astro_Wright
Replying to @zero132132 and 3 others
Right. We will make the data truly public eventually, somehow. Right now it's not mine to give away, and it's not in a final form we trust.

https://mobile.twitter.com/Astro_Wright/status/866826117071728643

Quote
Tabetha Boyajian @tsboyajian
Looking forward to what happens tonight with #tabbysstar . @kickstarter backers expect a full update tomorrow!

https://mobile.twitter.com/tsboyajian/status/866835203456724994
« Last Edit: 05/23/2017 06:26 am by Star One »

Offline sghill

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Re: Boyajians Star Updates And Discussion
« Reply #321 on: 05/23/2017 11:14 am »
Since we're speculating,  what would it look like if an icy giant gas planet regularly gets too close to a larger gas giant in orbit? Would it shed gas towards the larger body in a predictable spiral in a manner that we are now witnessing? Like two binary stars where one is parasitic, but much smaller and cooler, and the gas is replenished on a regular cycle, so you'd get a "hole", and then a "screen" pattern like in the previous "Synestia" image here: http://forum.nasaspaceflight.com/index.php?topic=41704.msg1681766#msg1681766

.

« Last Edit: 05/23/2017 03:43 pm by sghill »
Bring the thunder!

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #322 on: 05/23/2017 02:05 pm »
Can anyone estimate why Jason Wright would be after this info?

Quote
1h
Jason Wright @Astro_Wright
Astro hive-mind:
How do I get an ephemeris for @NASAKepler from @NASAJPL Horizons? I want x,y,z in barycentric frame.

Jason Wright @Astro_Wright

Replying to @Astro_Wright and 2 others
I tried getting distance, RA, DEC from vantage of SSB (site @0) but I get "Barycentric OBSERVER table disallowed -- consider body-center 10"

https://mobile.twitter.com/Astro_Wright/status/866995929236287488
« Last Edit: 05/23/2017 02:05 pm by Star One »

Offline jgoldader

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Re: Boyajians Star Updates And Discussion
« Reply #323 on: 05/23/2017 02:41 pm »
Can anyone estimate why Jason Wright would be after this info?

Quote
1h
Jason Wright @Astro_Wright
Astro hive-mind:
How do I get an ephemeris for @NASAKepler from @NASAJPL Horizons? I want x,y,z in barycentric frame.

Jason Wright @Astro_Wright

Replying to @Astro_Wright and 2 others
I tried getting distance, RA, DEC from vantage of SSB (site @0) but I get "Barycentric OBSERVER table disallowed -- consider body-center 10"

https://mobile.twitter.com/Astro_Wright/status/866995929236287488

When you're looking at transits/occultations/etc., the time the observer sees the event depends on the location of the observer, because the light travel time from the event itself to the observer depends on the position of the observer.  Suppose one observer on Earth was looking at, oh, say an extrasolar planet transiting its star.  That observer would probably measure different ingress/egress times than would, say, the Kepler satellite, because the Earth and Kepler are most likely at different distances from the event.

For occultations/transits/etc., I believe the general practice is to correct times to heliocentric julian date, though perhaps they're using the solar system barycenter (which is what I suspect the "SSB" means).  So it would seem somebody's looking to transform the time of an observation made by Kepler, to the time the light would have been seen by an observer at the solar system barycenter, or perhaps vice versa.
Recovering astronomer

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #324 on: 05/23/2017 02:43 pm »
Can anyone estimate why Jason Wright would be after this info?

Quote
1h
Jason Wright @Astro_Wright
Astro hive-mind:
How do I get an ephemeris for @NASAKepler from @NASAJPL Horizons? I want x,y,z in barycentric frame.

Jason Wright @Astro_Wright

Replying to @Astro_Wright and 2 others
I tried getting distance, RA, DEC from vantage of SSB (site @0) but I get "Barycentric OBSERVER table disallowed -- consider body-center 10"

https://mobile.twitter.com/Astro_Wright/status/866995929236287488

When you're looking at transits/occultations/etc., the time the observer sees the event depends on the location of the observer, because the light travel time from the event itself to the observer depends on the position of the observer.  Suppose one observer on Earth was looking at, oh, say an extrasolar planet transiting its star.  That observer would probably measure different ingress/egress times than would, say, the Kepler satellite, because the Earth and Kepler are most likely at different distances from the event.

For occultations/transits/etc., I believe the general practice is to correct times to heliocentric julian date, though perhaps they're using the solar system barycenter (which is what I suspect the "SSB" means).  So it would seem somebody's looking to transform the time of an observation made by Kepler, to the time the light would have been seen by an observer at the solar system barycenter, or perhaps vice versa.

Thank you.

You'd think JPL might have software that can work this out for investigators/researchers.

Offline jebbo

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Re: Boyajians Star Updates And Discussion
« Reply #325 on: 05/23/2017 03:28 pm »
For occultations/transits/etc., I believe the general practice is to correct times to heliocentric julian date, though perhaps they're using the solar system barycenter (which is what I suspect the "SSB" means).  So it would seem somebody's looking to transform the time of an observation made by Kepler, to the time the light would have been seen by an observer at the solar system barycenter, or perhaps vice versa.

Kepler uses Barycentric Julian Date

--- Tony

Online JasonAW3

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Re: Boyajians Star Updates And Discussion
« Reply #326 on: 05/23/2017 06:07 pm »
I may have missed it, but has the star started brightening again yet?
My God!  It's full of universes!

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #327 on: 05/23/2017 06:44 pm »
I may have missed it, but has the star started brightening again yet?

It's back to normal at the moment.

Quote
Tabetha Boyajian @tsboyajian

Replying to @Apnoespock and @kickstarter
we have a few holes, and of course weather gets in the way too, but we have been fortunate over that

https://mobile.twitter.com/tsboyajian/status/867060889056403456

Online JasonAW3

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Re: Boyajians Star Updates And Discussion
« Reply #328 on: 05/23/2017 08:07 pm »
I may have missed it, but has the star started brightening again yet?

It's back to normal at the moment.

Quote
Tabetha Boyajian @tsboyajian

Replying to @Apnoespock and @kickstarter
we have a few holes, and of course weather gets in the way too, but we have been fortunate over that

https://mobile.twitter.com/tsboyajian/status/867060889056403456

So I guesx that they don't hve the light curve and duration figures compiled just yet.
My God!  It's full of universes!

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #329 on: 05/23/2017 08:08 pm »
I may have missed it, but has the star started brightening again yet?

It's back to normal at the moment.

Quote
Tabetha Boyajian @tsboyajian

Replying to @Apnoespock and @kickstarter
we have a few holes, and of course weather gets in the way too, but we have been fortunate over that

https://mobile.twitter.com/tsboyajian/status/867060889056403456

So I guesx that they don't hve the light curve and duration figures compiled just yet.

Sounds like they are working on it with the Kickstart supporters first in line for an update.

Offline hop

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Re: Boyajians Star Updates And Discussion
« Reply #330 on: 05/24/2017 02:41 am »
New paper KIC 8462852: Will the Trojans return in 2021? Fernando J. Ballesteros, Pablo Arnalte-Mur, Alberto Fernandez-Soto, Vicent J. Martinez (submitted, not yet reviewed / accepted)

Quote
KIC 8462852 stood out among more than 100,000 stars in the Kepler catalogue because of the strange features of its light curve: a wide and asymmetric dimming taking up to 15 per cent of the total light, together with a period of multiple, narrow dimmings happening approximately 700 days later. Several models have been proposed to account for this abnormal behaviour, most of which require either unlikely causes or a finely-tuned timing. 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.

Trojans are a clever way to get a ~700 day period without having the dust warm enough to exceed observational limits, but the trojan clouds need to be extremely massive and/or dusty. The larger orbit also greatly relaxes constraints from radial velocity. The authors specifically note that it doesn't address the long term dimming. They suggest the most recent dip is compatible with a secondary eclipse of the planet.

My overall impression is interesting and not totally implausible, but not really satisfying.

Offline launchwatcher

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Re: Boyajians Star Updates And Discussion
« Reply #331 on: 05/24/2017 04:43 am »
Since we're speculating,  what would it look like if an icy giant gas planet regularly gets too close to a larger gas giant in orbit?

I would assume a close pass would perturb the orbits of both bodies so it wouldn't keep happening.   It might even eject the smaller planet entirely...

Offline as58

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Re: Boyajians Star Updates And Discussion
« Reply #332 on: 05/24/2017 06:04 am »
New paper KIC 8462852: Will the Trojans return in 2021? Fernando J. Ballesteros, Pablo Arnalte-Mur, Alberto Fernandez-Soto, Vicent J. Martinez (submitted, not yet reviewed / accepted)

Quote
KIC 8462852 stood out among more than 100,000 stars in the Kepler catalogue because of the strange features of its light curve: a wide and asymmetric dimming taking up to 15 per cent of the total light, together with a period of multiple, narrow dimmings happening approximately 700 days later. Several models have been proposed to account for this abnormal behaviour, most of which require either unlikely causes or a finely-tuned timing. 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.

Trojans are a clever way to get a ~700 day period without having the dust warm enough to exceed observational limits, but the trojan clouds need to be extremely massive and/or dusty. The larger orbit also greatly relaxes constraints from radial velocity. The authors specifically note that it doesn't address the long term dimming. They suggest the most recent dip is compatible with a secondary eclipse of the planet.

My overall impression is interesting and not totally implausible, but not really satisfying.

The secondary eclipse explanation feels a bit suspect. I don't see why the light curve would be so flat right until the secondary eclipse happens while the phase angle keeps changing.

edit: What I mean is that if a non-negligible fraction of observed flux in 'normal' state is scattered off planet/rings, I think there should be more modulation throughout the Kepler lightcurve as the planet moves around its orbit.
« Last Edit: 05/24/2017 06:07 am by as58 »

Offline high road

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Re: Boyajians Star Updates And Discussion
« Reply #333 on: 05/24/2017 07:04 am »
I may have missed it, but has the star started brightening again yet?

It's back to normal at the moment.


Well, for this particular star, 'normal' means it's back to dimming slowly rather than dipping fast.  ;)

Offline jebbo

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Re: Boyajians Star Updates And Discussion
« Reply #334 on: 05/24/2017 07:27 am »
My overall impression is interesting and not totally implausible, but not really satisfying.

Yes, interesting but I think it has some serious issues:
- the proposed planet has a radius ~5RJ.  That makes is a star which we'd see in IR at minimum
- the asymmetry of the supposed primary transit worries me. Impact parameter b = ~0.6 I understand, but I don't think rings really explain the smooth but asymmetric ingress and egress.
- others have mentioned ring stability. These are huge, covering most of the Hill sphere I think; hard to see how they're stable
- as stated in the paper, it does not explain the secular decline
- as as58 above, I'm dubious about the secondary as well

Edit: more on the secondary. For it to be a 3% dip says there is a LOT of reflected light, so yes, I'd expect phase modulation.

Edit2: perhaps we *are* seeing phase modulation.  See  figure 3 of Ben Montet's paper (https://arxiv.org/abs/1608.01316).

But nevertheless, it is still interesting ...

--- Tony
« Last Edit: 05/24/2017 07:48 am by jebbo »

Offline jebbo

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Re: Boyajians Star Updates And Discussion
« Reply #335 on: 05/24/2017 07:28 am »
Sounds like they are working on it with the Kickstart supporters first in line for an update.

Sadly, I won't see the update until tomorrow as I don't have access to the right email until I get home :-/

--- Tony

Offline Alpha_Centauri

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Re: Boyajians Star Updates And Discussion
« Reply #336 on: 05/24/2017 07:44 am »
Not a lot of new info yet. Just the data showing the event is pretty much over and a photo of the whiteboard showing many of the facilities that got data, which is a bit more than has been already stated. Tabby does say there should be short but regular updates in due course.
« Last Edit: 05/24/2017 07:44 am by Alpha_Centauri »

Offline Star One

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Re: Boyajians Star Updates And Discussion
« Reply #337 on: 05/24/2017 07:50 am »
Be interesting to see if it now goes into a vast dip because the best fit that Jason Wright was suggesting for this dip, last time I saw from the Kepler data was just before one of these.

Offline jebbo

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Re: Boyajians Star Updates And Discussion
« Reply #338 on: 05/24/2017 07:52 am »
Be interesting to see if it now goes into a vast dip because the best fit that Jason Wright was suggesting for this dip, last time I saw from the Kepler data was just before one of these.

Yes indeed. That is the good thing about the rings + trojans idea: it is eminently testable!

--- Tony

Offline as58

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Re: Boyajians Star Updates And Discussion
« Reply #339 on: 05/24/2017 08:14 am »
Edit2: perhaps we *are* seeing phase modulation.  See  figure 3 of Ben Montet's paper (https://arxiv.org/abs/1608.01316).

I'm not seeing phase modulation in that figure, or at least nothing consistent with a ~700 day period orbit...

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