Modelling a high-mass red giant observed by CoRoT

TL;DR

This study analyzes CoRoT observations of the G6 giant HR 2582, identifying solar-like oscillations and modeling its properties to determine its mass, evolutionary stage, and internal structure.

Contribution

The paper provides the first detailed seismic analysis of HR 2582, estimating its mass, evolutionary stage, and internal mixing parameters through combined observational and modeling approaches.

Findings

HR 2582 is a massive star (3-5 M_sun) above the red clump.

Detected solar-like oscillations with regular frequency spacing.

Models suggest the star is either on the ascending red giant branch or in a later phase.

Abstract

The G6 giant HR\,2582 (HD\,50890) was observed by CoRoT for approximately 55 days. Mode frequencies are extracted from the observed Fourier spectrum of the light curve. Numerical stellar models are then computed to determine the characteristics of the star (mass, age, etc...) from the comparison with observational constraints. We provide evidence for the presence of solar-like oscillations at low frequency, between 10 and 20\,$\mu$Hz, with a regular spacing of $(1.7\pm0.1)\mu$Hz between consecutive radial orders. Only radial modes are clearly visible. From the models compatible with the observational constraints used here, We find that HR\,2582 (HD\,50890) is a massive star with a mass in the range (3--\,5\,$M_{\odot}$), clearly above the red clump. It oscillates with rather low radial order ($n$ = 5\,--\,12) modes. Its evolutionary stage cannot be determined with precision: the star could be on the ascending red giant branch (hydrogen shell burning) with an age of approximately 155 Myr or in a later phase (helium burning). In order to obtain a reasonable helium amount, the metallicity of the star must be quite subsolar. Our best models are obtained with a mixing length significantly smaller than that obtained for the Sun with the same physical description (except overshoot). The amount of core overshoot during the main-sequence phase is found to be mild, of the order of 0.1\,$H_{\rm p}$.