# Eclipse and transit of HD 80606b

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## Re: Eclipse and transit of HD 80606b

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

Sedna
Planetary Embryo

Number of posts : 83
Registration date : 2008-08-21

## Re: Eclipse and transit of HD 80606b

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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Sirius_Alpha

Number of posts : 3655
Location : Earth
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## Re: Eclipse and transit of HD 80606b

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?

Edasich
dM star

Number of posts : 1545
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## Re: Eclipse and transit of HD 80606b

Volume of a sphere?

Lazarus
dF star

Number of posts : 2978
Registration date : 2008-06-12

## Re: Eclipse and transit of HD 80606b

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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Sirius_Alpha

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## Re: Eclipse and transit of HD 80606b

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.

Edasich
dM star

Number of posts : 1545
Location : Tau Ceti g - Mid Latitudes
Registration date : 2008-06-02

## Re: Eclipse and transit of HD 80606b

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.

Sedna
Planetary Embryo

Number of posts : 83
Registration date : 2008-08-21

## Re: Eclipse and transit of HD 80606b

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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Sirius_Alpha

Number of posts : 3655
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## Re: Eclipse and transit of HD 80606b

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

Sedna
Planetary Embryo

Number of posts : 83
Registration date : 2008-08-21

## Re: Eclipse and transit of HD 80606b

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

tesh90
Meteor

Number of posts : 29
Registration date : 2008-06-16

## Re: Eclipse and transit of HD 80606b

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Observation of the full 12-hour-long transit of the exoplanet HD80606b. Warm-Spitzer photometry and SOPHIE spectroscopyhttp://fr.arxiv.org/abs/1004.0790

lodp
Asteroid

Number of posts : 57
Location : Leeds, UK
Registration date : 2009-08-11

## Re: Eclipse and transit of HD 80606b

That transit is from January.

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

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Sirius_Alpha

Number of posts : 3655
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