A Super-Earth at Gliese 15

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A Super-Earth at Gliese 15

Post by Sirius_Alpha on 25th August 2014, 8:55 pm

The NASA-UC-UH Eta-Earth Program: IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth
http://arxiv.org/abs/1408.5645

We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab is a planet with minimum mass Msini = 5.35 0.75 M ⊕ , orbital period P = 11.4433 0.0016 days, and an orbit that is consistent with circular. We characterize the host star using a variety of techniques. Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of ~0.1 mmag, thus supporting the existence of the planet. We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features, as confirmed by optical photometry and the Ca II H & K activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we measure an M2 V spectral type and a sub-solar metallicity ([M/H] = -0.22, [Fe/H] = -0.32). We measure a stellar radius of 0.3863 0.0021 R ⊙ based on interferometry from CHARA.

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Re: A Super-Earth at Gliese 15

Post by Edasich on 26th August 2014, 3:56 am

Also known as Groombridge 34 A (or GX Andromedae). We're knowing always better our own "neighbours". Very Happy
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Re: A Super-Earth at Gliese 15

Post by Shellface on 26th August 2014, 10:38 am

Boy, that paper has a painfully mundane title.

But it's good to see the Eta-Earth survey is still doing things, considering they haven't published anything for a few years. I hope they've worked on their candidates from back then!

This planetary system is one more in a relatively close (~100 AU) binary. It is encouraging to see that the planet does not have a high eccentricity, which argues for either alignment between the stellar orbit and the protoplanetary disk, or that the planet formed close-in enough so that it could not be reached by Kozai oscillations to a high degree. Both circumstances are interesting, particularly the latter considering that the star is so late type that the ice line should be rather close-in, too.

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Re: A Super-Earth at Gliese 15

Post by Lazarus on 26th August 2014, 3:43 pm

Minimum mass is very close to or exceeding the value for an Earth-composition planet at the rocky/gaseous transition (which appears to occur at 1.5--1.6 Earth radii). I'd guess this one is likely a gas dwarf/sub-Neptune.
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