L 363-38 b: A planet newly discovered with ESPRESSO orbiting a nearby M dwarf star

Abstract

Context. Planets around stars in the solar neighbourhood will be prime targets for characterisation with upcoming large space- and ground-based facilities. Since large-scale exoplanet searches will not be feasible with such telescopes, it is crucial to use currently available data and instruments to find possible target planets before next-generation facilities come online.
Aims: We aim to detect new extrasolar planets around stars in the solar neighbourhood via blind radial velocity (RV) searching with ESPRESSO. Our target sample consists of nearby stars (d < 11 pc) with few (<10) or no previous RV measurements.
Methods: We used 31 radial velocity measurements obtained with ESPRESSO at the VLT between December 2020 and February 2022 of the nearby M dwarf star (M_★ = 0.21 M_⊙, d = 10.23 pc) L 363-38 to derive the orbital parameters of the newly discovered planet. In addition, we used TESS photometry and archival VLT/NaCo high-contrast imaging data to put further constraints on the orbit inclination and the possible planetary system architecture around L 363-38.
Results: We present the detection of a new extrasolar planet orbiting the nearby M dwarf star L 363-38. L 363-38 b is a planet with a minimum mass of m_p sin(i) = 4.67 ± 0.43 M_⊕ orbiting its star with a period of P = 8.781 ± 0.007 days, corresponding to a semi-major axis of a = 0.048 ± 0.006 AU, which is smaller than the inner edge of the habitable zone. We further estimate a minimum radius of r_p sin(i) ≈ 1.55-2.75 R_⊕ and an equilibrium temperature of T_eq ≈ 330 K.
Conclusions: With this study, we further demonstrate the potential of the state-of-the-art spectrograph ESPRESSO in detecting and investigating planetary systems around nearby M dwarf stars, which were inaccessible to previous instruments such HARPS.