The CARMENES search for exoplanets around M dwarfs Detection of a mini-Neptune around LSPM J2116+0234 and refinement of orbital parameters of a super-Earth around GJ 686 (BD+18 3421)

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S. Lalitha, D. Baroch, J. C. Morales, V. M. Passegger, F. F. Bauer, C. Cardona Guillén, S. Dreizler, M. Oshagh, A. Reiners, I. Ribas, J. A. Caballero, A. Quirrenbach, P. J. Amado, V. J. S. Béjar, J. Colomé, M. Cortés-Contreras, D. Galadí-Enríquez, L. González-Cuesta, E. W. Guenther, H.-J. Hagen, T. Henning, E. Herrero, T.-O. Husser, S. V. Jeffers, A. Kaminski, M. Kürster, M. Lafarga, N. Lodieu, M. J. López-González, D. Montes, M. Perger, A. Rosich, E. Rodríguez, C. Rodríguez-López, J. H. M. M. Schmitt, L. Tal-Or and M. Zechmeister. 2019. The CARMENES search for exoplanets around M dwarfs Detection of a mini-Neptune around LSPM J2116+0234 and refinement of orbital parameters of a super-Earth around GJ 686 (BD+18 3421). Astronomy and Astrophysics 627, DOI: 10.1051/0004-6361/201935534

Although M dwarfs are known for high levels of stellar activity, they are ideal targets for the search of low-mass exoplanets with the radial velocity (RV) method. We report the discovery of a planetary-mass companion around LSPM J2116+0234 (M3.0 V) and confirm the existence of a planet orbiting GJ 686 (BD+18 3421; M1.0 V). The discovery of the planet around LSPM J2116+0234 is based on CARMENES RV observations in the visual and near-infrared channels. We confirm the planet orbiting around GJ 686 by analyzing the RV data spanning over two decades of observations from CARMENES VIS, HARPS-N, HARPS, and HIRES. We find planetary signals at 14.44 and 15.53 d in the RV data for LSPM J2116+0234 and GJ 686, respectively. Additionally, the RV, photometric time series, and various spectroscopic indicators show hints of variations of 42 d for LSPM J2116+0234 and 37 d for GJ 686, which we attribute to the stellar rotation periods. The orbital parameters of the planets are modeled with Keplerian fits together with correlated noise from the stellar activity. A mini-Neptune with a minimum mass of 11.8 M-circle plus orbits LSPM J2116+0234 producing a RV semiamplitude of 6.19 m s(-1), while a super-Earth of mass 6.6 M-circle plus orbits GJ 686 and produces a RV semi-amplitude of 3.0 m s(-1). Both LSPM J2116+0234 and GJ 686 have planetary companions populating the regime of exoplanets with masses lower than 15 M-circle plus and orbital periods < 20 d.

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