Institution(s): 1. Beijing Normal University
Knowledge of the properties of the Galactic halo is of utmost importance because it helps us to describe the image of the early Galaxy. Recently, APOKASC catalog has released spectroscopic and asteroseismic parameters of more than 1600 RGB stars, including 40 Galactic halo stars. We purpose to estimate fundamental properties of these stars, especially the age. Additionally, we hope to present the relationship of stellar age and the value of [alpha/Fe], for the giant halo stars.
The Galactic halo stars are generally with alpha-enhanced metal mixture. With the information of alpha-element abundances presented by SDSS DR12, we divide these stars into two groups, one is alpha-poor group and the other is alpha-rich group. We contribute large amount of stellar evolution models to estimate stellar age, with observed spectroscopic constraints and asteroseismic constraints. It seems that stars with higher alpha abundance have an older age than those with low alpha abundance.