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trinitree88
2009-Sep-15, 11:12 PM
More and more, astronomers find subtle techniques to search for extrasolar Earths. The authors(Melendez, Asplund, Gustafsson,Yong...) find that the sun's unusual depletion in refractory elements...(read...the stuff that makes up terrestrial planets like Mercury, Venus,Earth, and Mars...) is due to exactly that, the presence of a planetary system around a sun-like star. This could lead to a spectroscopic signature in sun-like "twin" stars, that helps us hunt for another Earth.
They cautiously maintain that the sample is small, about a dozen....but the technique looks promising. pete


SEE:http://arxiv.org/PS_cache/arxiv/pdf/0909/0909.2299v1.pdf

timb
2009-Sep-16, 12:34 AM
More and more, astronomers find subtle techniques to search for extrasolar Earths. The authors(Melendez, Asplund, Gustafsson,Yong...) find that the sun's unusual depletion in refractory elements...(read...the stuff that makes up terrestrial planets like Mercury, Venus,Earth, and Mars...) is due to exactly that, the presence of a planetary system around a sun-like star. This could lead to a spectroscopic signature in sun-like "twin" stars, that helps us hunt for another Earth.
They cautiously maintain that the sample is small, about a dozen....but the technique looks promising. pete


SEE:http://arxiv.org/PS_cache/arxiv/pdf/0909/0909.2299v1.pdf

That's funny because the conclusion didn't make the assertion you attribute to it when I read it.

trinitree88
2009-Sep-16, 10:44 AM
That's funny because the conclusion didn't make the assertion you attribute to it when I read it.

timb. True, they considered several mechanisms for the abundance pattern, but it is quite obvious from their statement that they hope to use the signature...Quote" It is an entralling prospect to be able to identify stars with planetary systems similar to the Solar system by means of their abundance patterns..." end of quote....from the last paragraph of their conclusions.
pete

timb
2009-Sep-17, 06:17 AM
A prospect is not something you have already achieved. Elsewhere they qualify their conclusion. Their work is interesting but I think needs to be tested against many more exoplanets. CoRoT-7 has been confirmed as hosting a rocky planet: what is it's abundance signature?

Hungry4info
2009-Sep-17, 07:57 AM
CoRoT-7 has been confirmed as hosting a rocky planet: what is it's abundance signature?

Slightly above solar, [Fe/H] = +0.03 dex

timb
2009-Sep-17, 10:26 AM
Thanks for looking it up. Is that above or below what would be expected for a star of its age?

Hungry4info
2009-Sep-17, 08:29 PM
Thanks for looking it up.Not a problem, I keep information like that stored away where I can access it at any time. :)


Is that above or below what would be expected for a star of its age?
There doesn't seem to be much of a relationship between age and metallicity, as metallicity of the star is of primordial origin, and set by the metallicity of the parent nebula from which it formed. Here's some values, you can see they're all over the place. So, no, CoRoT-7 doesn't seem to be outside the "norm" as far as metallicity goes.


<table>
<tr><td>Star </td><td>[Fe/H] </td><td>Age(Gyr)</td></tr>
<tr><td>HD 47536 </td><td>-0.68 dex</td><td>9.33 Gyr</td></tr>
<tr><td>HD 139357</td><td>-0.13 dex</td><td>3.07 Gyr</td></tr>
<tr><td>HAT-P-3 </td><td> 0.24 dex</td><td>0.4 Gyr</td></tr>
<tr><td>CoRoT-7 </td><td> 0.03 dex</td><td>1.5 Gyr</td></tr>
<tr><td>Chi Vir </td><td> 0.19 dex</td><td>0.86 Gyr</td></tr>
<tr><td>HAT-P-1 </td><td> 0.13 dex</td><td>3.6 Gyr</td></tr>
</table>

timb
2009-Sep-17, 08:56 PM
Nice HTML. Metallicities should decrease with age because the average metallicity of nebulae is increasing. I've noticed that metallicities seem to vary quite a lot between similar stars, which makes me a little skeptical about plans to infer the presence of terrestrial planets. OTOH, maybe planets are the factor which will explain the hitherto mysterious variations.
Actually CoRoT-7 may not be relevant to testing the theory because the paper suggests that "hot" planets don't count. In fact other papers have suggested that giant planets are correlated with high metallicity. Why hot planets don't count is something I didn't comprehend on my first reading of the paper.

Hungry4info
2009-Sep-18, 12:48 AM
Actually CoRoT-7 may not be relevant to testing the theory because the paper suggests that "hot" planets don't count. In fact other papers have suggested that giant planets are correlated with high metallicity. Why hot planets don't count is something I didn't comprehend on my first reading of the paper.

Interesting. Maybe because hot planets haven't yet made it to contaminating their stars. I read a paper somewhere (http://arxiv.org/abs/0901.2048) that suggests that most short period planets eventually spiral inward.

timb
2009-Sep-18, 03:39 AM
Rereading the paper it is a little more subtle than that. They suggest that some solar analogs are relatively depleted in refractories because they accreted gas that was depleted in refractories after their convective zone had settled down. They suggest that, in at least the case of the Sun, the missing refractories (which mostly form compounds we would call "rock") condensed to form the terrestrial planets (or formed dust that was blown away). The fact that stars with hot jupiters don't show the depletion, can be taken to indicate (my reasoning) that the conditions under which hot jupiters form

prevent the condensation of refactories, or
prevent the accretion of left over refractory depleted gas, or
cause the accretion to happen earlier, before the star's convective zone has settled down.

George
2009-Sep-18, 04:02 AM
Just messin' around. Now that football season is here, here's a quick hail Mary given the data from Hungry4info. :)

timb
2009-Sep-18, 10:21 AM
That's a rather small sample, but it shows the relationship I referred to. The paper says the "twins" were age matched to the Sun, but doesn't say anything about the age of the "analogs". :(

Hungry4info
2009-Sep-18, 11:34 AM
I can provide dozens of points if you really want it. With my rather limited knowledge of Excel, I can produce the following, which does faintly seem to show a trend (other than planet hosts being preferentially above solar metallicity).
http://i159.photobucket.com/albums/t137/CrossingStyx/Age-metallicity.jpg

timb
2009-Sep-18, 11:00 PM
Your scatterplot has two stars that are older than the universe.

George
2009-Sep-19, 03:41 PM
I can provide dozens of points if you really want it. With my rather limited knowledge of Excel, I can produce the following, which does faintly seem to show a trend (other than planet hosts being preferentially above solar metallicity).
I wonder how that compares to non-planetary stars?

Hungry4info
2009-Sep-20, 07:58 AM
Your scatterplot has two stars that are older than the universe.

Yes, those were HD 4203, and XO-5.

I checked the Extrasolar Encyclopaedia Encyclopaedia (which is where I thought I got the information from) and they give more reasonable ages of 9.4 and 8.5 Gyr, respectively.

Deeply concerning that I had two stars in there that were older than the Universe. I'll go double check the ages of all of them later. In the mean time, ignore that whole scatter plot. =|

Thanks for pointing that out.