Planetary system around LTT 1445A unveiled by ESPRESSO: Multiple planets in a triple M-dwarf system
Bouchy, F.; Rebolo, R.; Allende Prieto, C.; Palle, E.; Poretti, E.; Cristiani, S.; Sozzetti, A.; Mehner, A.; Deline, A.; Adibekyan, V.; Alibert, Y.; Ehrenreich, D.; Lovis, C.; Udry, S.; Pepe, F.; Sousa, S.; Lillo-Box, J.; Micela, G.; D'Odorico, V.; Di Marcantonio, P.; Figueira, P.; González Hernández, J. I.; Lo Curto, G.; Martins, C. J. A. P.; Molaro, P.; Suárez Mascareño, A.; Damasso, M.; Lavie, B.; Santos, N.; Rodrigues, J.; Génova Santos, R.; Zapatero Osorio, M.; Barros, S.; Nunes, N.; Tabrenero, H.
Switzerland, Spain, Portugal, Chile, Italy, Germany
Abstract
We present radial velocity follow-up obtained with ESPRESSO of the M-type star LTT 1445A (TOI-455), for which a transiting planet b with an orbital period of 5.4 days was detected by TESS. We report the discovery of a second transiting planet (LTT 1445A c) and a third non-transiting candidate planet (LTT 1445A d) with orbital periods of 3.12 and 24.30 days, respectively. The host star is the main component of a triple M-dwarf system at a distance of 6.9 pc. We used 84 ESPRESSO high-resolution spectra to determine accurate masses of 2.3 ± 0.3 M⊕ and 1.0 ± 0.2 M⊕ for planets b and c and a minimum mass of 2.7 ± 0.7 M⊕ for planet d. Based on its radius of 1.43 ± 0.09 R⊕ as derived from the TESS observations, LTT 1445A b has a lower density than the Earth and may therefore hold a sizeable atmosphere, which makes it a prime target for the James Webb Space Telescope (JWST). We used a Bayesian inference approach with the nested sampling algorithm and a set of models to test the robustness of the retrieved physical values of the system. There is a probability of 85% that the transit of planet c is grazing, which results in a retrieved radius with large uncertainties at 1.60−0.34+0.67 R⊕. LTT 1445A d orbits the inner boundary of the habitable zone of its host star and could be a prime target for the JWST.
RV and activity indices for ESPRESSO are only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/673/A69