The CARMENES search for exoplanets around M dwarfs: a low-mass planet in the temperate zone of the nearby K2-18
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...
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| Main Authors: | , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
31 May 2018
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| In: |
The astronomical journal
Year: 2018, Volume: 155, Issue: 6 |
| ISSN: | 1538-3881 |
| DOI: | 10.3847/1538-3881/aac108 |
| Online Access: | Verlag, Volltext: https://doi.org/10.3847/1538-3881/aac108
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| Author Notes: | Paula Sarkis, Thomas Henning, Martin Kürster, Trifon Trifonov, Mathias Zechmeister, Lev Tal-Or, Guillem Anglada-Escudé, Artie P. Hatzes, Marina Lafarga, Stefan Dreizler, Ignasi Ribas, José A. Caballero, Ansgar Reiners, Matthias Mallonn, Juan C. Morales, Adrian Kaminski, Jesús Aceituno, Pedro J. Amado, Victor J.S. Béjar, Hans-Jürgen Hagen, Sandra Jeffers, Andreas Quirrenbach, Ralf Launhardt, Christopher Marvin, and David Montes |
| Summary: | 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. |
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| Item Description: | Gesehen am 20.05.2019 |
| Physical Description: | Online Resource |
| ISSN: | 1538-3881 |
| DOI: | 10.3847/1538-3881/aac108 |