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)

• Published in: Astronomy and astrophysics (Berlin) 2019-07, Vol.627, p.A116
• Main Authors: Lalitha, S., Baroch, D., Morales, J. C., Passegger, V. M., Bauer, F. F., Cardona Guillén, C., Dreizler, S., Oshagh, M., Reiners, A., Ribas, I., Caballero, J. A., Quirrenbach, A., Amado, P. J., Béjar, V. J. S., Colomé, J., Cortés-Contreras, M., Galadí-Enríquez, D., González-Cuesta, L., Guenther, E. W., Hagen, H.-J., Henning, T., Herrero, E., Husser, T.-O., Jeffers, S. V., Kaminski, A., Kürster, M., Lafarga, M., Lodieu, N., López-González, M. J., Montes, D., Perger, M., Rosich, A., Rodríguez, E., Rodríguez-López, C., Schmitt, J. H. M. M., Tal-Or, L., Zechmeister, M.
• Format: Article
• Language: English
• ISSN: 0004-6361; 1432-0746
• 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 observationsfrom 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 ⊕ orbits LSPM J2116+0234 producing a RV semi-amplitude of 6.19 m s −1 , while a super-Earth of mass 6.6 M ⊕ 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 ⊕ and orbital periods