TESS Asteroseismic Analysis of HD 76920: The Giant Star Hosting An Extremely Eccentric Exoplanet

TL;DR

This study uses TESS data to perform a detailed asteroseismic analysis of the giant star HD 76920, refining its stellar parameters and updating the characteristics of its highly eccentric exoplanet, predicting its eventual engulfment.

Contribution

First detection of solar-like oscillations in HD 76920 with TESS, leading to improved stellar and planetary parameter estimates and insights into the planet's future evolution.

Findings

Detected solar-like oscillations at 52 μHz in HD 76920.

Refined stellar mass to 1.22 M_sun and radius to 8.68 R_sun.

Updated planetary semi-major axis to 1.165 au and mass to 3.57 M_Jup.

Abstract

The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing for detailed asteroseismic studies of individual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet ($e = 0.878$) with an orbital period of 415 days, using 5 sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around $52 \, \mu$Hz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass ($1.22 \pm 0.11\, M_\odot$), radius ($8.68 \pm 0.34\,R_\odot$), and age ($5.2 \pm 1.4\,$Gyr). With the updated parameters of the host star, we update the semi-major axis and mass of the planet as $a=1.165 \pm 0.035$ au and $M_{\rm p}\sin{i} = 3.57 \pm 0.22\,M_{\rm Jup}$. With an orbital pericenter of $0.142 \pm 0.005$ au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100\,Myr, depending on the stellar model used.