Barragán, O.O.BarragánAigrain, S.S.AigrainKubyshkina, D.D.KubyshkinaGandolfi, D.D.GandolfiLivingston, J.J.LivingstonFridlund, M. C. V.M. C. V.FridlundFossati, L.L.FossatiKorth, J.J.KorthParviainen, H.H.ParviainenMalavolta, LucaLucaMalavoltaPalle, E.E.PalleDeeg, H. J.H. J.DeegNowak, G.G.NowakRajpaul, V. M.V. M.RajpaulZicher, N.N.ZicherAntoniciello, G.G.AntonicielloNarita, N.N.NaritaAlbrecht, S.S.AlbrechtBEDIN, LuigiLuigiBEDINCabrera, J.J.CabreraCochran, W. D.W. D.Cochrande Leon, J.J.de LeonEigmüller, PhPhEigmüllerFukui, A.A.FukuiGranata, V.V.GranataGrziwa, S.S.GrziwaGuenther, E.E.GuentherHatzes, A. P.A. P.HatzesKusakabe, N.N.KusakabeLatham, D. W.D. W.LathamLibralato, M.M.LibralatoLuque, R.R.LuqueMontañés-Rodríguez, P.P.Montañés-RodríguezMurgas, F.F.MurgasNardiello, D.D.NardielloPAGANO, IsabellaIsabellaPAGANOPiotto, G.G.PiottoPersson, C. M.C. M.PerssonRedfield, S.S.RedfieldTamura, M.M.Tamura2021-02-222021-02-2220190035-8711http://hdl.handle.net/20.500.12386/30530We present a detailed analysis of HARPS-N radial velocity observations of K2-100, a young and active star in the Praesepe cluster, which hosts a transiting planet with a period of 1.7 d. We model the activity-induced radial velocity variations of the host star with a multidimensional Gaussian Process framework and detect a planetary signal of 10.6 ± 3.0 {m s^{-1}}, which matches the transit ephemeris, and translates to a planet mass of 21.8 ± 6.2 M<SUB>⊕</SUB>. We perform a suite of validation tests to confirm that our detected signal is genuine. This is the first mass measurement for a transiting planet in a young open cluster. The relatively low density of the planet, 2.04 _{ - 0.61 } ^ { + 0.66 } {g cm^{-3}}, implies that K2-100b retains a significant volatile envelope. We estimate that the planet is losing its atmosphere at a rate of 10^{11}-10^{12} {g s^{-1}} due to the high level of radiation it receives from its host star.STAMPAenArticle10.1093/mnras/stz25692-s2.0-85075236110000496922300051http://arxiv.org/abs/1909.05252v1https://academic.oup.com/mnras/article/490/1/698/55696692019MNRAS.490..698BFIS/05 - ASTRONOMIA E ASTROFISICA