upsilon And b is an oddball ?

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upsilon And b is an oddball ?

Post by exoplanet on 27th November 2008, 7:57 pm

Hi,

I have been trying to find some more info on upsilon And b regarding the supposed large temperature gradients between the day and night sides of the planet observed by Spitzer a few years ago.This seems to be atypical (unique as far as I know) of other hot Jupiters, which apparently are very efficient at redistributing heat in the atmosphere.

Have these observations been confirmed ? The fit to the data points seemed like a bit of a stretch to me:

http://www.centauri-dreams.org/wp-content/uploads/2006/10/upsilon_andromedae_b.jpg

Any new info on this ? Is there any proposed mechanism that might explain this apparent unique behavior ?

Cheers

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Re: upsilon And b is an oddball ?

Post by Sirius_Alpha on 27th November 2008, 9:02 pm

If I remember, it was pretty much confirmed when they announced it a few years ago.

As far as I know, only HD 189733 b, HD 149026 b, Ups And b and HD 209458 b have been studied really indepth (and I think a TrES planet, too, but not to this level of detail). In all honesty, each of them seem unique in their own right.

I'm not sure if Ups And b is truly an oddball. You're right in that it's unique about being the only known planet that is poor at heat redistribution. Maybe this happens in 25% of hot Jupiters? Maybe 1%? We need more information, really.

As for proposed mechanisms, I really don't know. I haven't been keeping up with hot Jupiter atmospheric modelling over the past year. Sad

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Re: upsilon And b is an oddball ?

Post by exoplanet on 27th November 2008, 9:22 pm

This article mentions also 51 Peg b and HD179949b also with apparent small gradients:

http://uwnews.washington.edu/ni/article.asp?articleID=29397

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Re: upsilon And b is an oddball ?

Post by Sirius_Alpha on 27th November 2008, 9:56 pm

51 Pegasi b and HD 179949 b have never been directly detected, but there was a hint of detecting a transit of a possible tail from 51 Pegasi b (similar to HD 209458 b), and HD 179949 b is known to induce some X-ray activity on its host star. Outside of models, we know nothing about their atmospheres.

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Re: upsilon And b is an oddball ?

Post by Lazarus on 2nd December 2008, 12:45 pm

In fact the paper associated with the press release about 51 Peg, HD 179949 and HD 209458 actually mentions that phase variations were detected for HD 179949b, so it seems to have little redistribution over the surface. Also the very high temperatures observed on HD 149026b may indicate that very little redistribution is going on.

In fact, using the stellar parameters from this paper for the transiting planets and this paper for the nontransiting planets, it turns out that the planets go in decreasing order of effective temperature:

HD 149026 b
ups And b
HD 179949 b
HD 209458 b
51 Peg b
HD 189733 b

So it looks like the planets which have had large temperature variations detected are hotter than the ones which seem to have uniform temperatures. This also fits in nicely with the proposed pM/pL classification system: HD 189733 b is in the cooler pL class, while HD 209458 b is in the pM/pL transition region. Among several properties expected for these classes, pM class planets are expected to be poor at redistributing heat to the dark side, while more efficient redistribution is expected in pL class planets. See this paper.
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Re: upsilon And b is an oddball ?

Post by Sirius_Alpha on 2nd December 2008, 8:53 pm

Ahh... I was completely unaware that HD 179949 b was directly detected. Thank-you for that paper!

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Re: upsilon And b is an oddball ?

Post by exoplanet on 3rd December 2008, 10:02 am

Thanks Lazarus for that link and for your explanation. Interesting stuff as usual Smile

Cheers,

Luis

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