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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Re: A Super-Earth at Gliese 15

Post by Led_Zep on 5th October 2017, 2:34 pm

https://arxiv.org/abs/1710.01595

The CARMENES search for exoplanets around M dwarfs. First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems

Context: The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M-dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ15A, GJ176, GJ436, GJ536 and GJ1148) or are multiple planetary systems (GJ581 and GJ876).
Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES.
Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems are fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability.
Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ15A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ15Ab, we show evidence for a possible long-period (P c = 7025 +972 −629 d) Saturn-mass (m c sini = 51.8 +5.5 −5.8 M ⊕ ) planet around GJ15A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ1148, for which we estimate a period P c = 532.6 +4.1 −2.5 d, eccentricity e c = 0.34 +0.05 −0.06 and minimum mass m c sini = 68.1 +4.9 −2.2 M ⊕ .
Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars
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Re: A Super-Earth at Gliese 15

Post by Lazarus on 5th October 2017, 3:34 pm

Also worth noting that the eccentricity of Gliese 876 d comes out as a far lower value than previous solutions, which puts it in line with the prediction that tidal circularisation should be fast.
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Re: A Super-Earth at Gliese 15

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