TOI-199 b: A well-characterized 100-day transiting warm giant planet with TTVs seen from Antarctica

Abstract

We present the spectroscopic confirmation and precise mass measurement of the warm giant planet TOI-199 b. This planet was first identified in TESS photometry and confirmed using ground-based photometry from ASTEP in Antarctica including a full 6.5h long transit, PEST, Hazelwood, and LCO; space photometry from NEOSSat; and radial velocities (RVs) from FEROS, HARPS, CORALIE, and CHIRON. Orbiting a late G-type star, TOI-199\,b has a $104.854_{-0.002}^{+0.001}\mathrm{d}$ period, a mass of $0.17\pm 0.02{\mathrm{M}}_{\mathrm{J}}$, and a radius of $0.810\pm 0.005{\mathrm{R}}_{\mathrm{J}}$. It is the first warm exo-Saturn with a precisely determined mass and radius. The TESS and ASTEP transits show strong transit timing variations, pointing to the existence of a second planet in the system. The joint analysis of the RVs and TTVs provides a unique solution for the non-transiting companion TOI-199 c, which has a period of $273.69_{-0.22}^{+0.26}\mathrm{d}$ and an estimated mass of $0.28_{-0.01}^{+0.02}{\mathrm{M}}_{\mathrm{J}}$. This period places it within the conservative Habitable Zone.

33 pages, 23 figures. Accepted for publication in AJ