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  The CARMENES Search for Exoplanets around M Dwarfs: A Low-mass Planet in the Temperate Zone of the Nearby K2-18

Sarkis, P., Henning, T., Kürster, M., Trifonov, T., Zechmeister, M., Tal-Or, L., et al. (2018). The CARMENES Search for Exoplanets around M Dwarfs: A Low-mass Planet in the Temperate Zone of the Nearby K2-18. The Astronomical Journal, 155.

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 Creators:
Sarkis, Paula1, Author
Henning, Thomas1, Author
Kürster, Martin1, Author
Trifonov, Trifon1, Author
Zechmeister, Mathias1, Author
Tal-Or, Lev1, Author
Anglada-Escudé, Guillem1, Author
Hatzes, Artie P.1, Author
Lafarga, Marina1, Author
Dreizler, Stefan1, Author
Ribas, Ignasi1, Author
Caballero, José A.1, Author
Reiners, Ansgar1, Author
Mallonn, Matthias1, Author
Morales, Juan C.1, Author
Kaminski, Adrian1, Author
Aceituno, Jesús1, Author
Amado, Pedro J.1, Author
Béjar, Victor J. S.1, Author
Hagen, Hans-Jürgen1, Author
Jeffers, Sandra1, AuthorQuirrenbach, Andreas1, AuthorLaunhardt, Ralf1, AuthorMarvin, Christopher1, AuthorMontes, David1, Author more..
Affiliations:
1Max Planck Institute for Astronomy, Max Planck Society and Cooperation Partners, ou_2421692              

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Free keywords: stars: activity stars: individual: K2-18 stars: low-mass Astrophysics - Earth and Planetary Astrophysics
 Abstract: K2-18 is a nearby M2.5 dwarf, located at 34 pc and hosting a transiting planet that was first discovered by the K2 mission and later confirmed with Spitzer Space Telescope observations. With a radius of ̃2 R and an orbital period of ̃33 days, the planet lies in the temperate zone of its host star and receives stellar irradiation similar to that of Earth. Here we perform radial velocity follow-up observations with the visual channel of CARMENES with the goal of determining the mass and density of the planet. We measure a planetary semi-amplitude of K b ̃ 3.5 {{m}} {{{s}}}-1 and a mass of M b ̃ 9 M , yielding a bulk density around {ρ }b̃ 4 {{g}} {cm}}-3. This indicates a low-mass planet with a composition consistent with a solid core and a volatile- rich envelope. A signal at 9 days was recently reported using radial velocity measurements taken with the HARPS spectrograph. This was interpreted as being due to a second planet. We see a weaker, time- and wavelength-dependent signal in the CARMENES data set and thus favor stellar activity for its origin. K2-18 b joins the growing group of low- mass planets detected in the temperate zone of M dwarfs. The brightness of the host star in the near-infrared makes the system a good target for detailed atmospheric studies with the James Webb Space Telescope.

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 Dates: 2018
 Publication Status: Issued
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Title: The Astronomical Journal
Source Genre: Journal
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Pages: - Volume / Issue: 155 Sequence Number: - Start / End Page: - Identifier: -