MOA-2008-BLG-310Lb - planet in the Galactic Bulge

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MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Sirius_Alpha on 5th August 2009, 8:13 pm

Sub-Saturn Planet MOA-2008-BLG-310Lb: Likely To Be In The Galactic Bulge
http://arxiv.org/abs/0908.0529

Abstract wrote:We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and argue that it is the strongest candidate yet for a bulge planet. Deviations from the single-lens fit are smoothed out by finite-source effects and so are not immediately apparent from the light curve. Nevertheless, we find that a model in which the primary has a planetary companion is favored over the single-lens model by \Delta\chi^2 ~ 880 for an additional three degrees of freedom. Detailed analysis yields a planet/star mass ratio q=(3.3+/-0.3)x10^{-4} and an angular separation between the planet and star within 10% of the angular Einstein radius. The small angular Einstein radius, \theta_E=0.155+/-0.011 mas, constrains the distance to the lens to be D_L>6.0 kpc if it is a star (M_L>0.08 M_sun). This is the only microlensing exoplanet host discovered so far that must be in the bulge if it is a star. By analyzing VLT NACO adaptive optics images taken near the baseline of the event, we detect additional blended light that is aligned to within 130 mas of the lensed source. This light is plausibly from the lens, but could also be due to a companion to lens or source, or possibly an unassociated star. If the blended light is indeed due to the lens, we can estimate the mass of the lens, M_L=0.67+/-0.14 M_sun, planet mass m=74+/-17 M_Earth, and projected separation between the planet and host, 1.25+/-0.10 AU, putting it right on the "snow line". If not, then the planet has lower mass, is closer to its host and is colder. To distinguish among these possibilities on reasonable timescales would require obtaining Hubble Space Telescope images almost immediately, before the source-lens relative motion of \mu=5 mas yr^{-1} causes them to separate substantially.

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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Stalker on 6th August 2009, 4:00 am

what is the Galactic Bulge?
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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Sirius_Alpha on 6th August 2009, 4:06 am

Stalker wrote:what is the Galactic Bulge?

It's the "fat part" of the centre of the galaxy. Labeled "Nuclear bulge" here in this picture.


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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Stalker on 6th August 2009, 4:24 am

Have you got a French translation of the word "Bulge"?
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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Lazarus on 6th August 2009, 4:27 am

Bulbe galactique according to the French Wikipedia equivalent of the English page about this concept...
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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Stalker on 6th August 2009, 4:48 am

Thanks
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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Edasich on 6th August 2009, 11:31 am

Interesting the fact that such a sub-saturnian planet would lay within system's snowline. Assuming host star's mass around 0.67 MSun (and a putative radius and luminosity of 0.77 RSun and 0.29 LSun respectively) the habitable zone should be located around 0.54 AUs or less.

If the planet is 1.25 AUs far away from host star, doing the math we get an equivalent separation of 2.3 AUs, just between Mars and Jupiter's orbital zones.
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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

Post by Lazarus on 6th August 2009, 6:51 pm

IIRC the cold super-Earth OGLE-2005-BLG-390Lb is also thought to be located in the bulge, but I guess it is not so well constrained.

Formation of planets in such an environment (old but fairly metal rich stars) has various interesting implications.
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Re: MOA-2008-BLG-310Lb - planet in the Galactic Bulge

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