CORALIE radial-velocity search for companions around evolved stars (CASCADES)

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 ± 0.10 M⊙ and 1.59 ± 0.08 MJup, 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.

Constraints on planetary tidal dissipation from a detailed study of Kepler 91b

“…of the tidal dissipation by orders of magnitude are obtained as a result of the evolution of the internal stellar structure (Rao et al 2018). This illustrates the need to correctly follow the internal structure of the star during these evolutionary phases, which can either be done by computing full models of the star as in the present study or in our previous works (Pezzotti et al 2021b(Pezzotti et al ,a, 2022Bétrisey et al 2022), or by using pre-calculated grids of stellar models that provide the needed quantities M env and R env, as done for instance by Bolmont & Mathis (2016).…”

CORALIE radial-velocity search for companions around evolved stars (CASCADES)

“…For reasons of consistency and reliability of the data post-processing (mainly correction of saturation and camera focus stability due to instrumental issues), we have to consider this data with caution when using it to check for variability due to intrinsic stellar processes or surface rotational modulation. We discuss this matter in more detail in Pezzotti et al (2022). No periodicities linked to the ones detected in the radial-velocity data have been found for any of the three stars presented in this paper.…”

“…Asteroseismologic analysis can provide precious information concerning the past and future evolution of such systems. Among the highly interesting related questions is the one of the impact of stellar evolution on the planet orbits and of the potential engulfment of planets by the star (Pezzotti et al 2022), for instance to explain the apparent lack of close-in, short-period planets (P 100 days, a 0.5 au). The second and third publications of the CAS-CADES series will focus on the asteroseimic analysis of the three stellar hosts presented in this paper (Buldgen et al 2022) and the analysis of a new planet-host star (Pezzotti et al 2022), for which the full evolution of the system can be modeled.…”