HADES RV Programme with HARPS-N at TNG. VI. GJ 3942 b behind dominant activity signals
Rebolo, R.; Ribas, I.; Morales, J. C.; Scandariato, G.; Pagano, I.; Lafarga, M.; Poretti, E.; Rainer, M.; Sozzetti, A.; Maldonado, J.; Esposito, M.; Nascimbeni, V.; Borsa, F.; Micela, G.; González Hernández, J. I.; Suárez Mascareño, A.; Leto, G.; Zanmar Sanchez, R.; Toledo-Padrón, B.; Damasso, M.; Affer, L.; Benatti, S.; Claudi, R.; Desidera, S.; Martinez Fiorenzano, A. F.; Molinari, E.; Pedani, M.; Herrero, E.; Bignamini, A.; Perger, M.; Carbognani, A.; Rosich, A.
Spain, Italy, Switzerland, France
Abstract
Context. Short- to mid-term magnetic phenomena on the stellar surface of M-type stars can resemble the effects of planets in radial velocity data, and may also hide them.
Aims: We analyze 145 spectroscopic HARPS-N observations of GJ 3942 taken over the past five years and additional photometry in order to disentangle stellar activity effects from genuine Doppler signals as a result of the orbital motion of the star around the common barycenter with its planet.
Methods: To achieve this, we use the common methods of pre-whitening, and treat the correlated red noise by a first-order moving average term and by Gaussian-process regression following an MCMC analysis.
Results: We identify the rotational period of the star at 16.3 days and discover a new super-Earth, GJ 3942 b, with an orbital period of 6.9 days and a minimum mass of 7.1 M⊕. An additional signal in the periodogram of the residuals is present, but at this point we cannot claim with sufficient significance that it is related to a second planet. If confirmed, this planet candidate would have a minimum mass of 6.3 M⊕ and a period of 10.4 days, which might indicate a 3:2 mean-motion resonance with the inner planet.