A Cold and Super-Puffy Planet on a Prograde Orbit

Abstract

We report the discovery of TOI-4507 b, a transiting sub-Saturn with a density $<$ 0.2 g/cm${}^3$ on a 105-day prograde orbit around a 700 Myr old F star. The transits were detected using data from TESS as well as the Antarctic telescope ASTEP. A joint analysis of the light curves and radial velocities from HARPS, FEROS, and CORALIE confirmed the planetary nature of the signal by limiting the mass to be below 20 $M_{\oplus }$ at 95% confidence. The radial velocities also exhibit the Rossiter-McLaughlin effect and imply that the planet orbits the star in a prograde orbit with a sky-projected obliquity $\hat{I}»=-15_{-44}^{+50}$ deg ($|\hat{I}»|<80$ deg at $3\ddot{I}ƒ$). With these characteristics, TOI-4507 is one of the longest-period systems for which the stellar obliquity has been measured, and the planet is among the longest-period and youngest ''super-puff'' planets yet discovered.

15 pages, 4 figures. Accepted for publication in ApJL