Characteristics of solar-like oscillations of secondary red-clump stars

Author： Yang Wuming Meng Xiangcun Bi Shaolan Tian Zhijia Liu Kang Li Tanda Li Zhongmu

ISSN： 0035-8711

Source： Monthly Notices of the Royal Astronomical Society, Vol.422, Iss.2, 2012-05, pp. : 1552-1561

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Abstract

ABSTRACTWe 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 (∆ν) of CHeB stars when metallicity Z≥ 0.02. The ν_max and ∆ν 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_HeF significantly. 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_max distribution. 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 ∆ν for populations with M > M_HeF is obviously larger than that for populations with M < M_HeF.