Probing the cores of RGB Bump stars with asteroseismic l=1 modes

Ning Gai, Department of Physics, Dezhou University, ning_gai@163.com

Abstract
The "bump" is an intrinsic feature of the red giant branch (RGB)luminosity function of globular clusters. The bump originates when the H-burning shell crosses the chemical discontinuity left over by the convective envelope soon after the first dredge-up. During the RGB Bump phase, a low-mass star crosses the same luminosity interval three times. Asteroseismology is a powerful tool to probe the internal structure of stars which have the same luminosity and very similar temperatures. We use the periodicity in the small separations between modes of l = 0, 1 to probe the different positions of the HeII ionisation layer and the base of the convective envelope. The average period spacing of RGB Bump stars are monotonic decrease with evolution, but there is a convoluted variation at the bottom of RGB Bump.