A super-Earth on a close-in orbit around the M1V star GJ 740. A HADES and CARMENES collaboration
Rebolo, R.; Amado, P. J.; Caballero, J. A.; Reiners, A.; Ribas, I.; Quirrenbach, A.; Morales, J. C.; Zechmeister, M.; Scandariato, G.; Pagano, I.; Sozzetti, A.; Giacobbe, P.; Maldonado, J.; Micela, G.; González Hernández, J. I.; Suárez Mascareño, A.; Leto, G.; Toledo-Padrón, B.; Damasso, M.; Affer, L.; Desidera, S.; Pinamonti, M.; Herrero, E.; Perger, M.; Zanmar Sánchez, R.; González-Alvarez, E.
Spain, Italy, Germany
Abstract
Context. M-dwarfs have proven to be ideal targets for planetary radial velocity (RV) searches due to their higher planet-star mass contrast, which favors the detection of low-mass planets. The abundance of super-Earth and Earth-like planets detected around this type of star motivates further such research on hosts without reported planetary companions.
Aims: The HADES and CARMENES programs are aimed at carrying out extensive searches of exoplanetary systems around M-type stars in the northern hemisphere, allowing us to address, in a statistical sense, the properties of the planets orbiting these objects. In this work, we perform a spectroscopic and photometric study of one of the program stars (GJ 740), which exhibits a short-period RV signal that is compatible with a planetary companion.
Methods: We carried out a spectroscopic analysis based on 129 HARPS-N spectra taken over a time span of 6 yr combined with 57 HARPS spectra taken over 4 yr, as well as 32 CARMENES spectra taken during more than 1 yr, resulting in a dataset with a time coverage of 10 yr. We also relied on 459 measurements from the public ASAS survey with a time-coverage of 8 yr, along with 5 yr of photometric magnitudes from the EXORAP project taken in the V, B, R, and I filters to carry out a photometric study. Both analyses were made using Markov chain Monte Carlo simulations and Gaussian process regression to model the activity of the star.
Results: We present the discovery of a short-period super-Earth with an orbital period of 2.37756−0.00011+0.00013 d and a minimum mass of 2.96−0.48+0.50 M⊕. We offer an update to the previously reported characterization of the magnetic cycle and rotation period of the star, obtaining values of Prot = 35.563 ± 0.071 d and Pcycle = 2800 ± 150 d. Furthermore, the RV time series exhibits a possibly periodic long-term signal, which might be related to a Saturn-mass planet of ~100 M⊕.