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

Abstract

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. <BR /> Aims: We validate the physical nature of two Neptune-sized planets transiting TOI-942 (TYC 5909-319-1), a previously unacknowledged young star (50<SUB>-20</SUB><SUP>+30</SUP> Myr) observed by the TESS space mission in Sector 5. <BR /> 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. <BR /> 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'<SUB>HK</SUB> = -4.17 ± 0.01) with rotation period P<SUB>rot</SUB> = 3.39 ± 0.01 days, a projected rotation velocity v sin i<SUB>⋆</SUB> = 13.8 ± 0.5 km s<SUP>-1</SUP>, and a radius of ~0.9 R<SUB>⊙</SUB>. We found that the inner planet, TOI-942 b, has an orbital period P<SUB>b</SUB> = 4.3263 ± 0.0011 days, a radius R<SUB>b</SUB> = 4.242<SUB>-0.313</SUB><SUP>+0.376</SUP> R<SUB>⊕</SUB>, and a mass upper limit of 16 M<SUB>⊕</SUB> at 1σ confidence level. The outer planet, TOI-942 c, has an orbital period P<SUB>c</SUB> = 10.1605<SUB>-0.0053</SUB><SUP>+0.0056</SUP> days, a radius R<SUB>c</SUB> = 4.793<SUB>-0.351</SUB><SUP>+0.410</SUP> R<SUB>⊕</SUB>, and a mass upper limit of 37 M<SUB>⊕</SUB> at 1σ confidence level. <P />Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain). <P />The authors became aware of a parallel effort on the characterization of TOI-942 by Zhou et al. (2021) in the late stages of the manuscript preparations. The submissions are coordinated, and no analyses or results were shared prior to submission.