TOI-1296b and TOI-1298b observed with TESS and SOPHIE: Two hot Saturn-mass exoplanets with different densities around metal-rich stars

TL;DR

This study reports the discovery and characterization of two Saturn-mass exoplanets around metal-rich stars, highlighting differences in their densities likely due to varying stellar irradiation levels, using TESS and SOPHIE data.

Contribution

First detailed characterization of two Saturn-mass exoplanets with differing densities around metal-rich stars using combined TESS photometry and SOPHIE radial velocity measurements.

Findings

TOI-1296b is a low-density planet with 1.2 RJup radius and 0.198 g/cm3 density.

TOI-1298b is a denser planet with 0.84 RJup radius and 0.743 g/cm3 density.

Both planets have similar masses (~0.3-0.36 MJup) and short orbital periods (~4 days).

Abstract

We present the discovery of two new transiting extrasolar planet candidates identified as TOI-1296.01 and TOI-1298.01 by the Transiting Exoplanet Survey Satellite (TESS). The planetary nature of these candidates has been secured with the SOPHIE high-precision spectrograph through the measurement of the companion's mass with the radial velocity method. Both planets are similar to Saturn in mass and have similar orbital periods of a few days. They, however, show discrepant radii and therefore different densities. The radius discrepancy might be explained by the different levels of irradiation by the host stars. The subgiant star TOI-1296 hosts a low-density planet with 1.2 RJup while the less luminous, lower-size star TOI-1298 hosts a much denser planet with a 0.84 RJup radius, resulting in bulk densities of 0.198 and 0.743 g/cm3, respectively. In addition, both stars are strongly enriched in heavy elements, having metallicities of 0.44 and 0.49 dex, respectively. The planet masses and orbital periods are 0.298 (0.039) MJup and 3.9443715 days for TOI-1296b, and 0.356 (0.032) MJup and 4.537164 days for TOI-1298b.