The GAPS Programme at TNG XXVIII -- A pair of hot-Neptunes orbiting the young star TOI-942

TL;DR

This study confirms two Neptune-sized planets orbiting the young star TOI-942, providing valuable data on planetary formation and evolution in a system less than 100 million years old.

Contribution

First validation of two Neptune-sized planets around a young star using combined photometric and spectroscopic data, including discovery of an additional transiting planet.

Findings

Inner planet: 4.3-day orbit, ~4.2 R_earth, mass <16 M_earth

Outer planet: 10.2-day orbit, ~4.8 R_earth, mass <37 M_earth

Star characterized as active K2.5V, age ~50 Myr

Abstract

Both young stars and multi-planet systems are primary objects that allow us to study, understand and constrain planetary formation and evolution theories. We validate the physical nature of two Neptune-type planets transiting TOI-942 (TYC 5909-319-1), a previously unacknowledged young star (50+30-20 Myr) observed by the TESS space mission in Sector 5. Thanks to a comprehensive stellar characterization, TESS light curve modelling and precise radial-velocity measurements, we validated the planetary nature of the TESS candidate and detect an additional transiting planet in the system on a larger orbit. 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 (logR'hk = -4.17+-0.01) with rotation period Prot = 3.39+-0.01 days, a projected rotation velocity vsini=13.8+-0.5 km/s and a radius of ~0.9 Rsun. We found that the inner planet, TOI-942b, has an orbital period Pb=4.3263+-0.0011 days, a radius Rb=4.242-0.313+0.376 Rearth and a mass upper limit of 16 Mearth at 1-sigma confidence level. The outer planet, TOI-942c, has an orbital period Pc=10.1605-0.0053+0.0056 days, a radius Rc=4.793-0.351+0.410 Rearth and a mass upper limit of 37 Mearth at 1-sigma confidence level.