Coralie radial-velocity search for companions around evolved stars (CASCADES) III. A new Jupiter host-star: in-depth analysis of HD 29399 using TESS data

TL;DR

This study reports the discovery and detailed analysis of a long-period giant planet orbiting the evolved star HD 29399, combining radial-velocity data, TESS photometry, and stellar modeling to understand the system's properties and orbital history.

Contribution

It provides a comprehensive characterization of HD 29399 and its planet, including stellar and planetary masses, age, and orbital evolution, using combined observational and modeling techniques.

Findings

Detected a long-period giant planet around HD 29399.

Derived stellar and planetary masses of 1.17 M_sun and 1.59 M_Jup.

Found no significant orbital evolution due to tides or future engulfment.

Abstract

Context. Increasing the number of detected exoplanets is far from anecdotal, especially for long-period planets that require a long duration of observation. More detections imply a better understanding of the statistical properties of exoplanet populations, and detailed modelling of their host stars also enables thorough discussions of star-planet interactions and orbital evolution of planetary systems. Aims. In the context of the discovery of a new planetary system, we aim to perform a complete study of HD 29399 and its companion by means of radial-velocity measurements, seismic characterisation of the host-star, and modelling of the orbital evolution of the system. Methods. High-resolution spectra of HD 29399 were acquired with the CORALIE spectrograph mounted on the 1.2- m Swiss telescope located at La Silla Observatory (Chile) as part of the CASCADES survey. We used the moments of the cross-correlation function profile as well as the photometric variability of the star as diagnostics to distinguish between stellar and planetary-induced signals. To model the host star we combined forward modelling with global and local minimisation approaches and inversion techniques. We also studied the orbital history of the system under the effects of both dynamical and equilibrium tides. Results. We present the detection of a long-period giant planet. Combining these measurements with photometric observations by TESS, we are able to thoroughly model the host star and study the orbital evolution of the system. We derive stellar and planetary masses of $1.17 \pm 0.10~ M_{\odot}$ and $1.59 \pm 0.08 ~M_{Jup}$, respectively, and an age for the system of 6.2 Gyr. We show that neither dynamical nor equilibrium tides have been able to affect the orbital evolution of the planet. Moreover, no engulfment is predicted for the future evolution of the system.