Asteroseismology of 19 low-luminosity red giant stars from Kepler

TL;DR

This study uses high-precision Kepler data to analyze 19 low-luminosity red giant stars, deriving stellar parameters through a forward modelling approach that improves accuracy over traditional scaling relations.

Contribution

It introduces a forward modelling technique combining seismic and spectroscopic data to more precisely determine stellar parameters of red giants.

Findings

Seismic-based parameters have lower errors than scaling relations.

Average error in log g is 0.002 dex, and in mass and radius are 2% and 0.5%.

Low-mass stars require higher overshooting parameters in models.

Abstract

Frequencies of acoustic and mixed modes in red giant stars are now determined with high precision thanks to the long continuous observations provided by the NASA Kepler mission. Here we consider the eigenfrequencies of nineteen low-luminosity red giant stars selected by Corsaro et al. (2015) for a detailed peak-bagging analysis. Our objective is to obtain stellar parameters by using individual mode frequencies and spectroscopic information. We use a forward modelling technique based on a minimization procedure combining the frequencies of the p modes, the period spacing of the dipolar modes, and the spectroscopic data. Consistent results between the forward modelling technique and values derived from the seismic scaling relations are found but the errors derived using the former technique are lower. The average error for log g is 0.002 dex, compared to 0.011 dex from the frequency of maximum power and 0.10 dex from the spectroscopic analysis. Relative errors in the masses and radii are on average 2 and 0.5 per cent respectively, compared to 3 and 2 per cent derived from the scaling relations. No reliable determination of the initial helium abundances and the mixing length parameters could be made. Finally, for our grid of models with a given input physics, we found that low-mass stars require higher values of the overshooting parameter.