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+0.001d period, a mass of
0.17±0.02MJ, and a radius of 0.810±0.005RJ.
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+0.26d and an estimated
mass of 0.28−0.01+0.02MJ. This period places it within
the conservative Habitable Zone.Comment: 33 pages, 23 figures. Accepted for publication in A