Eclipse and transit of HD 80606b

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Re: Eclipse and transit of HD 80606b

Post by Sedna on 11th April 2010, 8:31 am

That's right (101.653), but I still can't understand why there's such a high density in brown dwarfs.

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Re: Eclipse and transit of HD 80606b

Post by Sirius_Alpha on 11th April 2010, 9:14 am

High mass, low radius due to gravitational compression of the body.

... until the pressure at the core achieves the requirements for sustained nuclear fusion then the radius of the body sky-rockets and the density plummets.

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Re: Eclipse and transit of HD 80606b

Post by Edasich on 11th April 2010, 10:51 am

Now lame question: from mass and radius how do I get planet exact density in g/cc? I should divide mass by volume but have I got planet's volume?
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Re: Eclipse and transit of HD 80606b

Post by Lazarus on 11th April 2010, 11:01 am

Volume of a sphere?
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Re: Eclipse and transit of HD 80606b

Post by Sirius_Alpha on 11th April 2010, 1:03 pm

Basic high school geometry. Volume of a sphere is 4/3 π r3
And since we know that dp = mp / V

It's pretty easy to see where to go from there.

It should be permissible to use the transit radius as the radius of the planet, and neglect any oblateness effects, since the transit radius will be more-or-less the average radius of the planet.

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Re: Eclipse and transit of HD 80606b

Post by Edasich on 11th April 2010, 1:22 pm

I tried to get,for instance, the density of Corot-3 b:

M=21.66 Mj R=1.01 Rj d=25.6 g/cc

I find the sphere volume being V=4.188x(1.01)^3= 4.31

d= M/V= 21.66/4.31=5.02

Jupiter's density is 1.33 g/cc. Then I find 6.53 g/cc. While actually is 25.6 g/cc

I need some help

*EDIT*

Forget it. I've performed same calculations putting kg and km values and then converting into g/cc.
I roughly get right values.
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Re: Eclipse and transit of HD 80606b

Post by Sedna on 12th April 2010, 1:45 pm

Sirius_Alpha wrote:High mass, low radius due to gravitational compression of the body.

... until the pressure at the core achieves the requirements for sustained nuclear fusion then the radius of the body sky-rockets and the density plummets.

Okay, I understand now. But I always have the not-so-good idea that temperature elevation triggers gas' expansion.

Edasich wrote:I find the sphere volume being V=4.188x(1.01)^3= 4.31
...
Forget it. I've performed same calculations putting kg and km values and then converting into g/cc.
I roughly get right values.

That's why we have SI units...

To come back at the planet, I remember that I took a look at the properties and I found something weird and interesting but I don't know how it's possible. I think I should think of it before telling you.

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Re: Eclipse and transit of HD 80606b

Post by Sirius_Alpha on 12th April 2010, 2:59 pm

Yeah, the gas will want to expand as the temperature increases, but there's also the gravitational compression of the planet, which overcomes the tendency for the gas to expand due to the heat. This is why it takes a lot of matter for the pressure in the core to be high enough for fusion.

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Re: Eclipse and transit of HD 80606b

Post by Sedna on 13th April 2010, 1:17 pm

Thank you for these lines, now I will never get it wrong.

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Re: Eclipse and transit of HD 80606b

Post by tesh90 on 16th May 2010, 10:36 am

Sorry, no news but is there any news on the recent (end of april) transit?

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Re: Eclipse and transit of HD 80606b

Post by lodp on 17th May 2010, 2:52 pm

<tr></tr>

<table cellpadding="0" cellspacing="0"><tr><td>Observation of the full 12-hour-long transit of the
exoplanet HD80606b. Warm-Spitzer photometry and SOPHIE spectroscopy

http://fr.arxiv.org/abs/1004.0790
</td></tr></table>

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Re: Eclipse and transit of HD 80606b

Post by Sirius_Alpha on 17th May 2010, 7:17 pm

That transit is from January.

.... observation of HD80606 that covers the full transit of 13-14 January 2010

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Re: Eclipse and transit of HD 80606b

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