Mixed-mode Ensemble Asteroseismology of Low-luminosity Kepler Red Giants

Abstract

We present measurements of the dipole mode asymptotic period spacing (ΔΠ _1 ), the coupling factor between the p - and g -modes ( q ), the g -mode phase offset ( ϵ _g ), and the mixed-mode frequency rotational splitting ( δ ν _rot ) for 1074 low-luminosity red giants from the Kepler mission. Using oscillation mode frequencies extracted from each star, we apply Bayesian optimization to estimate ΔΠ _1 from the power spectrum of the stretched-period spectrum and to perform the subsequent forward modeling of the mixed-mode frequencies. With our measurements, we show that the mode coupling factor q shows significant anticorrelation with both the stellar mass and metallicity, and can reveal highly metal-poor stars. We present the evolution of ϵ _g up the lower giant branch up to before the luminosity bump, and find no significant trends in ϵ _g or δ ν _rot with the stellar mass and metallicity in our sample. Additionally, we identify six new red giants showing anomalous distortions in their g -mode pattern. Our data products, code, and results are provided in a public repository.

Keywords

• Asteroseismology
• Stellar properties
• Stellar oscillations
• Astronomy data analysis