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

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

doi:10.1051/0004-6361/202553719

paper

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

arXiv:2507.15763 · doi:10.1051/0004-6361/202553719

Abstract

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 $\pm$ 0.020 $R_{⊙}$ and a mass of $M_{⋆}$ = 0.577 $\pm$ 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 $\sim$ 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 $e = 0.25 \pm 0.04$ , an orbital period of $P \sim 5$ days, and an equilibrium temperature of $T_{e q} \sim 682 K$ . With a radius of $R_{p} = 1.84 \pm 0.08 R_{\oplus}$ (4% precision), a mass of $M_{p} = 4.5 7_{- 0.93}^{+ 0.89} M_{\oplus}$ (20% precision), and a mean density of $ρ_{p} = 4.0 3_{- 0.81}^{+ 0.49} g c m^{- 3}$ , 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.

arXiv commentAccepted for publication in A&A. 16 pages. 13 figures

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

Abstract

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