An ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685

TL;DR

This paper reports the discovery and characterization of TOI-1685 b, an ultra-short-period super-Earth orbiting an M3 dwarf, with precise mass, radius, and temperature measurements, and discusses its significance for planetary system evolution.

Contribution

The study provides the first precise dynamical mass and radius measurements of an ultra-short-period super-Earth around an M dwarf, highlighting its unique density and temperature properties.

Findings

TOI-1685 b has a mass of 3.78 Earth masses and radius of 1.70 Earth radii.

It has the lowest density among known ultra-short-period planets around M dwarfs.

The planet's high temperature makes it suitable for thermal emission spectroscopy.

Abstract

Dynamical histories of planetary systems, as well as atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of P_b=0.6691403+0.0000023-0.0000021 d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of M_b=3.78+/-0.63 M_Earth, a radius of R_b=1.70+/-0.07 R_Earth, which together result in a bulk density of rho_b=4.21+0.95-0.82 g/cm3, and an equilibrium temperature of Teq_b=1069+/-16 K. TOI-1685 b is the least dense ultra-short period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting Earth-size planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report a further non-transiting planet candidate in the system, TOI-1685[c], with an orbital period of P_[c]=9.02+0.10-0.12 d.