A possibly inflated planet around the bright young star DS Tucanae A

Abstract

Context. The origin of the observed diversity of planetary system architectures is one of the main topics of exoplanetary research. The detection of a statistically significant sample of planets around young stars allows us to study the early stages of planet formation and evolution, but only a handful are known so far. In this regard a considerable contribution is expected from the NASA TESS satellite, which is now performing a survey of 85% of the sky to search for short-period transiting planets. <BR /> Aims: In its first month of operation TESS found a planet candidate with an orbital period of 8.14 days around a member of the Tuc-Hor young association ( 40 Myr), the G6V main component of the binary system DS Tuc. If confirmed, it would be the first transiting planet around a young star suitable for radial velocity and/or atmospheric characterisation. Our aim is to validate the planetary nature of this companion and to measure its orbital and physical parameters. <BR /> Methods: We obtained accurate planet parameters by coupling an independent reprocessing of the TESS light curve with improved stellar parameters and the dilution caused by the binary companion; we analysed high-precision archival radial velocities to impose an upper limit of about 0.1 M<SUB>Jup</SUB> on the planet mass; we finally ruled out the presence of external companions beyond 40 au with adaptive optics images. <BR /> Results: We confirm the presence of a young giant (R = 0.50 R<SUB>Jup</SUB>) planet having a non-negligible possibility to be inflated (theoretical mass ≲ 20 M<SUB>⊕</SUB>) around DS Tuc A. We discuss the feasibility of mass determination, Rossiter-McLaughlin analysis, and atmosphere characterisation allowed by the brightness of the star. <P />Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 075.C-0202(A), 0102.C-0618(A), 0103.C-0759(A), 075.A-9010(A), 076.A-9006(A), 073.C-0834(A), 083.C-0150(B).This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST).