TOI-1736 and TOI-2141: two systems including sub-Neptunes around solar analogs revealed by TESS and SOPHIE

Abstract

Planetary systems around solar analogs inform us about how planets form and evolve in Solar System-like environments. We report the detection and characterization of two planetary systems around the solar analogs TOI-1736 and TOI-2141 using TESS photometry data and spectroscopic data obtained with the SOPHIE instrument on the 1.93 m telescope at the Observatoire de Haute-Provence (OHP). We performed a detailed spectroscopic analysis of these systems to obtain the precise radial velocities (RV) and physical properties of their host stars. TOI-1736 and TOI-2141 each host a transiting sub-Neptune with radii of $2.44\pm 0.18$ R${}_{\oplus }$ and $3.05\pm 0.23$ R${}_{\oplus }$, orbital periods of $7.073088(7)$ d and $18.26157(6)$ d, and masses of $12.8\pm 1.8$ M${}_{\oplus }$ and $24\pm 4$ M${}_{\oplus }$, respectively. TOI-1736 shows long-term RV variations that are consistent with a two-planet solution plus a linear trend of $-0.177$ ms${}^{-1}$d${}^{-1}$. We measured an RV semi-amplitude of $201.1\pm 0.7$ ms${}^{-1}$ for the outer companion, TOI-1736 c, implying a projected mass of $m_c\sin i=8.09\pm 0.20$ M${}_{\mathrm{Jup}}$. From the GAIA DR3 astrometric excess noise, we constrained the mass of TOI-1736 c at $8.7_{-0.6}^{+1.5}$ M${}_{\mathrm{Jup}}$. This planet is in an orbit of $570.2\pm 0.6$ d with an eccentricity of $0.362\pm 0.003$ and a semi-major axis of $1.381\pm 0.017$ au, where it receives a flux of $0.71\pm 0.08$ times the bolometric flux incident on Earth, making it an interesting case of a supergiant planet that has settled into an eccentric orbit in the habitable zone of a solar analog. Our analysis of the mass-radius relation for the transiting sub-Neptunes shows that both TOI-1736 b and TOI-2141 b likely have an Earth-like dense rocky core and a water-rich envelope.

Accepted for publication in A&A on October 6, 2023