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

TL;DR

This paper confirms and characterizes the warm giant exoplanet TOI-199 b using multi-source photometry and spectroscopy, revealing transit timing variations indicative of a second planet near the habitable zone.

Contribution

It provides the first precise mass and radius measurement of a warm exo-Saturn and detects a non-transiting companion through combined TTV and RV analysis.

Findings

TOI-199 b has a 104.85-day orbit, mass of 0.17 M_J, and radius of 0.81 R_J.

Transit timing variations suggest a second planet, TOI-199 c, with a 273.69-day period.

TOI-199 c's orbit lies within the conservative Habitable Zone.

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 6.5$\,$h 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 $\mathrm{104.854_{-0.002}^{+0.001} \, d}$ period, a mass of $\mathrm{0.17\pm0.02 \, M_J}$, and a radius of $\mathrm{0.810\pm0.005 \, R_J}$. 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 $\mathrm{273.69_{-0.22}^{+0.26} \, d}$ and an estimated mass of $\mathrm{0.28_{-0.01}^{+0.02} \, M_J}$. This period places it within the conservative Habitable Zone.