Towards Accurate Asteroseismic Masses for Luminous Giants

TL;DR

This paper improves the accuracy of asteroseismic mass measurements for luminous red giants by refining correction schemes, reducing systematic offsets, and enhancing agreement with Gaia data and stellar evolution models.

Contribution

It introduces an alternative correction formulation that minimizes sensitivity to density inference methods, significantly reducing mass and age discrepancies in luminous giants.

Findings

Reduced median mass discrepancy from 6.65% to 1.72%.

Lowered age discrepancy from -21.81% to -9.55%.

Improved agreement with surface C/N ratios in alpha-poor stars.

Abstract

Asteroseismology, the study of stellar oscillations, provides high-precision measurements of masses and ages for red giants. Scaling relations are a powerful tool for measuring fundamental stellar parameters, and the derived radii are in good agreement with fundamental data for low-luminosity giants. However, for luminous red giant branch (RGB) stars, there are clear systematic offsets. In APOKASC-3, the third joint spectroscopic and asteroseismic catalog for evolved stars in the Kepler fields, we tied asteroseismic radii to a reference system based on Gaia astrometry by introducing correction factors. This work proposes an alternative formulation of the correction scheme, which substantially reduces the sensitivity of the results to the technique used to infer mean density from frequency spacings. Compared to APOKASC-3, our adjusted correction scheme also reduces fractional discrepancies in median masses and ages of lower RGB and upper RGB within the $\alpha$-rich population from $6.65\%$ to $1.72\%$ and from $-21.81\%$ to $-9.55\%$, respectively. For the $\alpha$-poor population, the corrected mass scale leads to an improved agreement between theory and observation of the surface carbon-to-nitrogen abundance ratio, a significant diagnostic of the first dredge-up.