Why is it so hard to model red clump stars?
Lea Schimak (University of Sydney, Australia)
Asteroseismology has long been proven to be a powerful tool for probing the interior of stars and testing stellar models. For red clump (RC) stars, which experienced a He-flash in their past, these tests show limited success compared to main-sequence or red giant branch (RGB) stars of a similar mass range. The models are confronted with various discrepancies and numerical issues. For example, RC stars in clusters often provide inconsistent ages compared to their RGB counterparts; the observed period spacing suggests enhanced core overshooting; and at the convective core boundary, the models often predict a split convection zone due to the sharp changes in the composition gradient.
In this talk, I will present how standard models fail, what has been done to improve them and discuss different asteroseismic constraints to further investigate the discrepancies. I will explore standard models using the asteroseismic binary system KIC 1081730, consisting of an RC and RGB star and measure the frequency-dependent coupling strength of mixed modes as a surface-independent parameter to probe the inside of red giants and discuss how this parameter is an excellent probe, especially for the structure of RC stars.