Characterizing two solar-type Kepler subgiants with asteroseismology: KIC10920273 and KIC11395018

TL;DR

This study uses Kepler asteroseismology data combined with ground-based spectroscopy to precisely determine the fundamental properties of two evolved solar-type subgiants, revealing their distinct masses and ages and confirming their evolutionary status.

Contribution

The paper provides detailed asteroseismic modeling of two Kepler subgiants, improving the precision of their fundamental parameters and clarifying their evolutionary stages compared to previous estimates.

Findings

KIC10920273 is a 1.00 solar mass, 7.12 Gyr old subgiant.

KIC11395018 is a 1.27 solar mass, 4.57 Gyr old subgiant.

Both stars are evolved subgiants with high lithium abundance, not young stars.

Abstract

Determining fundamental properties of stars through stellar modeling has improved substantially due to recent advances in asteroseismology. Thanks to the unprecedented data quality obtained by space missions, particularly CoRoT and Kepler, invaluable information is extracted from the high-precision stellar oscillation frequencies, which provide very strong constraints on possible stellar models for a given set of classical observations. In this work, we have characterized two relatively faint stars, KIC10920273 and KIC11395018, using oscillation data from Kepler photometry and atmospheric constraints from ground-based spectroscopy. Both stars have very similar atmospheric properties; however, using the individual frequencies extracted from the Kepler data, we have determined quite distinct global properties, with increased precision compared to that of earlier results. We found that both stars have left the main sequence and characterized them as follows: KIC10920273 is a one-solar-mass star (M=1.00 +/- 0.04 M_sun), but much older than our Sun (t=7.12 +/- 0.47 Gyr), while KIC11395018 is significantly more massive than the Sun (M=1.27 +/- 0.04 M_sun) with an age close to that of the Sun (t=4.57 +/- 0.23 Gyr). We confirm that the high lithium abundance reported for these stars should not be considered to represent young ages, as we precisely determined them to be evolved subgiants. We discuss the use of surface lithium abundance, rotation and activity relations as potential age diagnostics.