Recently, ZHANG Qiansheng, Christensen-Dalsgaard and LI Yan from Yunnan Observatories and Aarhus University have found a constraint of the convective core overshoot in low-mass stars and a correlation between the strength of overshoot and the stellar mass. The results were published in Monthly Notices of the Royal Astronomical Society.

The convective overshoot mixing refreshes fuel in the stellar core and then prolongs the lifetime of stars. However, it is the largest uncertainty in the current theory of the stellar evolution. It is crucial for the stellar structure and evolution and the age determination of star clusters.

For the solar-mass stars, it is generally believed that there is no convective core. However, near the zero-age main sequence, the He3 fusion is efficient enough to drive a convective core in solar-mass stars. In the standard stellar evolutionary scenario, since the overshoot is not taken into account, the convective core will vanish in a short timescale, i.e., the He3 burning timescale about 1-10 Myr. When the overshoot is taken into account, the He3 in the core is refueled by the convective transport from the surround layer, which prolongs the lifetime of the convective core. This affects the structure of the core of stars. Therefore the observations sensitive to the core, e.g., helioseismic/asteroseismic data and the neutrino fluxes caused by nuclear fusion, can be used to probe the convective overshoot mixing in stellar interior.

Based on this idea, ZHANG, Christensen-Dalsgaard & LI have modeled the Sun and some Kepler solar-like stars with varied strength of the convective core overshoot mixing, and compared the helioseismic/asteroseismic properties and the solar neutrino fluxed of the stellar models with the observations. They have found that the range of the parameters of the overshoot mixing can be estimated. The results show that the strength of the convective core overshoot mixing increases with the stellar mass.

Contact:
ZHANG Qian-Sheng, Yunnan Observatories, Chinese Academy of Sciences
zqs@ynao.ac.cn