Two warm sub-Saturn mass planets identified from the TESS Full Frame Images

TL;DR

The study reports the discovery and detailed characterization of two transiting warm sub-Saturn planets, TOI-883 b and TOI-899 b, using TESS FFIs complemented by extensive ground-based follow-up. A joint photometry–RV analysis with juliet, including a GP treatment of TESS long-cadence data, yields precise masses (0.123 ± 0.012 M_J and 0.213 ± 0.024 M_J) and radii (0.604 ± 0.028 R_J and 0.991 ± 0.044 R_J) with orbital periods of 10.06 and 12.85 days, and equilibrium temperatures around 1040–1086 K. Despite similar host stars and orbital configurations, the planets display different internal compositions, suggesting distinct formation histories and enriching the sub-Saturn population that informs core accretion theories. Both planets are promising targets for atmospheric characterization and RM measurements to further elucidate their formation pathways and the physics of Neptune–Saturn-mass planets in moderate irradiation environments.

Abstract

Context. Characterization of warm giants is crucial to constrain giant planet formation and evolution. Measuring the mass and radius of these planets, combined with their moderated irradiation, allows us to estimate their planetary bulk composition, which is a key quantity to comprehend giant planet formation and structure. Aims. We present the discovery of two transiting warm giant planets orbiting solar-type stars from the Transiting Exoplanet Survey Satellite (TESS), which were characterized by further spectroscopic and photometric ground-based observations. Methods. We performed a joint analysis of photometric data with radial velocities to confirm and characterize TOI-883 b and TOI-899 b, two sub-Saturns orbiting solar-like stars. Results. TOI-883 b and TOI-899 b have masses of $0.123 \pm 0.012$ $M_J$ and $0.213 \pm 0.024$ $M_J$, radius of $0.604 \pm 0.028$ $R_J$ and $0.991 \pm 0.044$ $R_J$, periods of $10.06$ d and $12.85$ d and equilibrium temperature of $1086 \pm 19$ K and $1040 \pm 19$ K, respectively. Conclusions. While having similar masses, orbital periods and stellar host properties, these planets seem to have different internal compositions, which could point to distinct formation histories. Both planets are suitable targets for atmospheric studies to further constrain formation scenarios of planets in the Neptune-Saturn mass range

Figures (15)

• Figure 1: Speckle images for TOI-883 and TOI-899 obtained with the Southern Astrophysical Research (SOAR). Both observations show no evidence for close companions.
• Figure 2: Postage stamps for TOI-883 and TOI-899 (Sector 2), respectively, taken from the TESS FFIs. Orange dots correspond to nearby Gaia sources, with marker size proportional to their magnitude. Target location and aperture used to generate the light curve are plotted in red.
• Figure 3: Observed minus calculated diagram of all the transits observed for TOI-899b. No significant periodic signal was found in the data, ruling out an additional companion found via TTVs.
• Figure 4: TOI-899 as seen on TESS Sectors 1 to 8, which are only available in Long Cadence. As the field of view rotates, the star falls on different CCD, showing different shapes and neighborhoods, which can affect the noise of the light curve. The aperture chosen for each sector is highlighted in red.
• Figure 5: TESS Light curve for TOI-883. Top panel corresponds to long cadence data from Sector 6 and bottom panel short cadence from Sector 33.