Paper

Discovery of a transiting hot water-world candidate orbiting Ross 176 with TESS and CARMENES

Calatayud-Borras, Y, Lacedelli, G, Montes, D, Parviainen, H, Fernández-Rodríguez, G, Nagel, E, Ribas, I, Vanaverbeke, S, Lodieu, N, Murgas, F, Pallé, E, Trifonov, T, Geraldía-González, S, Orell-Miquel, J, Fukui, A, Mori, M, Béjar, V J S, Luque, R, Cifuentes, C, Caballero, J A, de Leon, J, Winn, J N, Schlecker, M, Schweitzer, A, Tabernero, H M, Narita, N, Seager, S, Duque-Arribas, C, Lillo-Box, J, Poultourtzidis, E, Morello, G, Stassun, K G, Reiners, A

2025

Overview

The case of Ross 176 is a late K-type star that hosts a promising water-world candidate planet. The star has a radius of \\(R_*\\)=0.569\\(\\)0.020\\(R_\\) and a mass of \\(M_\\) = 0.577 \\(\\) 0.024 \\(M_\\). We constrained the planetary mass using spectroscopic data from CARMENES, an instrument that has already played a major role in confirming the planetary nature of the transit signal detected by TESS. We used Gaussian Processes (GP) to improve the analysis because the host star has a relatively strong activity that affects the radial velocity dataset. In addition, we applied a GP to the TESS light curves to reduce the correlated noise in the detrended dataset. The stellar activity indicators show a strong signal that is related to the stellar rotation period of \\(\\) 32 days. This stellar activity signal was also confirmed on the TESS light curves. Ross 176b is an inner hot transiting planet with a low-eccentricity orbit of \\(e = 0.25 0.04\\), an orbital period of \\(P 5\\) days, and an equilibrium temperature of \\(T_eq 682K\\). With a radius of \\(R_p = 1.840.08R_\\) (4% precision), a mass of \\(M_p = 4.57^+0.89_-0.93 M_\\) (20% precision), and a mean density of \\(_p = 4.03^+0.49_-0.81 g cm^-3\\), the composition of Ross 176b might be consistent with a water-world scenario. Moreover, Ross 176b is a promising target for atmospheric characterization, which might lead to more information on the existence, formation and composition of water worlds. This detection increases the sample of planets orbiting K-type stars. This sample is valuable for investigating the valley of planets with small radii around this type of star. This study also shows that the dual detection of space- and ground-based telescopes is efficient for confirm new planets.

• Publisher: Cornell University Library, arXiv.org
• Subject: Composition / Datasets / Extrasolar planets / Gaussian process / K stars / Light curve / Planetary mass / Planetary orbits / Radial velocity / Stellar activity / Stellar rotation / Telescopes / Transit