2012MNRAS.422.1552Y

We calculated the populations of core-helium-burning (CHeB) stars and found that secondary red-clump (SRC) stars can form a SRC peak in the distributions of the frequency of maximum seismic amplitude (ν_max) and mean large-frequency separation (Δν) of CHeB stars when metallicity Z > 0.02. The ν_max and Δν of CHeB stars are dependent not only on He-core mass but also on H-shell burning. The SRC peak is composed of CHeB stars with mass roughly between the critical mass M_HeF and M_HeF+ 0.2, while He-core mass is between about 0.33 and 0.36 M_☉. The location of the SRC peak can be affected by the mixing-length parameter α, metallicity Z and overshooting parameter δ_ov. A decrease in α or increase in Z or δ_ov leads to a movement of the SRC peak towards a lower frequency. The change in Z and α only slightly affects the value of M_HeF, but the variation in δ_ov can affect the value of M_HeFsignificantly. Thus the SRC peak might aid in determining the value of M_HeF and calibrating δ_ov. In addition, the effects of convective acceleration of SRC stars and the decrease in the ν_max of `semidegenerate' stars with mass result in the appearance of a shoulder between about 40 and 50 µHz in the ν_maxdistribution. However, the convective acceleration of stars with M < M_HeF leads to a deficit in the ν_max distribution between about 9 and 20 µHz. Moreover, the value of the parameter b of the relation between ν_max and Δν for populations with M > M_HeF is obviously larger than that for populations with M < M_HeF. On the sodium overabundance of giants in open clusters: the case of the Hyades