2021A&A...645A..71C

Context. Young stars and multi-planet systems are two types of primary objects that allow us to study, understand, and constrain planetary formation and evolution theories.
Aims. We validate the physical nature of two Neptune-sized planets transiting TOI-942 (TYC 5909-319-1), a previously unacknowledged young star (50_–20^+30Myr) observed by the TESS space mission in Sector 5.
Methods. Thanks to a comprehensive stellar characterization, TESS light curve modeling and precise radial-velocity measurements, we validated the planetary nature of the TESS candidate and detected an additional transiting planet in the system on a larger orbit.
Results. From photometric and spectroscopic observations we performed an exhaustive stellar characterization and derived the main stellar parameters. TOI-942 is a relatively active K2.5V star (log R'_HK=-4.17±0.01) with rotation period P_rot=3.39±0.01 days, a projected rotation velocity vsini_*=13.8±0.5km/s, and a radius of ∼0.9R_☉. We found that the inner planet, TOI-942 b, has an orbital period P_b=4.3263±0.0011 days, a radius R_b=4.242_–0.313^+0.376R_⊕, and a mass upper limit of 16M_⊕ at 1σ confidence level. The outer planet, TOI-942 c, has an orbital period P_c=10.1605_–0.0053^+0.0056-days, a radius R_c=4.793_–0.351^+0.410R_⊕, and a mass upper limit of 37M_⊕ at 1σ confidence level.