Ensemble Asteroseismology for 138 Kepler Metal-poor Red Giants: Stellar Fundamental Parameters

Abstract We present the analysis of solar-like oscillations for 138 metal-poor red giants observed by Kepler. We extracted individual oscillation modes and used them to characterize stars via a detailed modeling approach. Our analysis shows that the mass and age estimates do not strongly depend on input metallicity and the mixing length parameters, differing from stars with solar metallicity. We also noticed a systematic bias in estimated parameters when modeling stars with only p -modes. The systematics can be reduced by using the properly scaled large separation as a prior in the fitting. We finally determine fundamental parameters with a typical precision of 2.3% for mass, 8.5% for age, 0.80% for radius, and 0.003 dex for surface gravity. We found that most stars below Fe/H ∼ −1.0 are older than 10 Gyr, which is consistent with Galactic formation history. However, the age estimates for approximately 10% of our stars exceed the accepted age of the Universe (13.7 Gyr) by a significant margin. This discrepancy may arise from substantial mass loss experienced by these stars or from systematic biases introduced by modeling assumptions and input physics. To assess the robustness of these age determinations, future studies employing different stellar evolution codes and varied model inputs are essential. Stars in this work with the high-precision fundamental parameters can be benchmarks that support future studies of the properties of metal-poor stars and the early history of the Galaxy.