TY - JOUR
T1 - The CARMENES Search for Exoplanets around M Dwarfs
T2 - A Low-mass Planet in the Temperate Zone of the Nearby K2-18
AU - Sarkis, Paula
AU - Henning, Thomas
AU - Kürster, Martin
AU - Trifonov, Trifon
AU - Zechmeister, Mathias
AU - Tal-Or, Lev
AU - Anglada-Escudé, Guillem
AU - Hatzes, Artie P.
AU - Lafarga, Marina
AU - Dreizler, Stefan
AU - Ribas, Ignasi
AU - Caballero, José A.
AU - Reiners, Ansgar
AU - Mallonn, Matthias
AU - Morales, Juan C.
AU - Kaminski, Adrian
AU - Aceituno, Jesús
AU - Amado, Pedro J.
AU - Béjar, Victor J.S.
AU - Hagen, Hans Jürgen
AU - Jeffers, Sandra
AU - Quirrenbach, Andreas
AU - Launhardt, Ralf
AU - Marvin, Christopher
AU - Montes, David
N1 - Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/6
Y1 - 2018/6
N2 - 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 and a mass of M b ∼ 9 M ⊕, yielding a bulk density around . 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.
AB - 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 and a mass of M b ∼ 9 M ⊕, yielding a bulk density around . 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.
KW - stars: activity
KW - stars: individual (K2-18)
KW - stars: low-mass
UR - https://www.scopus.com/pages/publications/85048230588
U2 - 10.3847/1538-3881/aac108
DO - 10.3847/1538-3881/aac108
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AN - SCOPUS:85048230588
SN - 0004-6256
VL - 155
JO - Astronomical Journal
JF - Astronomical Journal
IS - 6
M1 - 257
ER -