The masses of retired A stars with asteroseismology: Kepler and K2 observations of exoplanet hosts

TL;DR

This study uses asteroseismology to measure the masses of retired A stars, comparing them with spectroscopic estimates, and finds no strong systematic bias but highlights the importance of input uncertainties.

Contribution

It provides a detailed comparison of asteroseismic and spectroscopic mass estimates for retired A stars, addressing potential biases and the impact of input uncertainties.

Findings

Most spectroscopic masses exceed asteroseismic estimates but without systematic bias.

Differences depend on the reference literature and recovery constraints.

Underestimated uncertainties can bias stellar mass measurements.

Abstract

We investigate the masses of "retired A stars" using asteroseismic detections on seven low-luminosity red-giant and sub-giant stars observed by the NASA Kepler and K2 Missions. Our aim is to explore whether masses derived from spectroscopy and isochrone fitting may have been systematically overestimated. Our targets have all previously been subject to long term radial velocity observations to detect orbiting bodies, and satisfy the criteria used by Johnson et al. (2006) to select survey stars that may have had A-type (or early F-type) main-sequence progenitors. The sample actually spans a somewhat wider range in mass, from $\approx 1\,\rm M_{\odot}$ up to $\approx 1.7\,\rm M_{\odot}$. Whilst for five of the seven stars the reported discovery mass from spectroscopy exceeds the mass estimated using asteroseismology, there is no strong evidence for a significant, systematic bias across the sample. Moreover, comparisons with other masses from the literature show that the absolute scale of any differences is highly sensitive to the chosen reference literature mass, with the scatter between different literature masses significantly larger than reported error bars. We find that any mass difference can be explained through use of differing constraints during the recovery process. We also conclude that underestimated uncertainties on the input parameters can significantly bias the recovered stellar masses, which may have contributed to the controversy on the mass scale for retired A stars.