大样本恒星演化研究组知识库

Hot subdwarf stars, known as extreme horizontal branch stars in globular clusters, are important objects in many aspects, e.g., stellar evolution, distance indicators, Galactic Structure, and the long-standing problem of far-ultraviolet (far-UV) excess in early-type galaxies. In this talk, we review the current formation scenarios for hot subdwarf stars and discuss related problems, and then propose two new formation channels. The first channel is tidally enhanced stellar wind channel, in which a first giant branch (FGB) star experiences an enhanced stellar wind mass loss due to the proximity of its companion star and becomes a hot subdwarf if most of the envelope is lost. Such a channel can produce extreme horizontal branch stars, blue horizontal branch stars and red horizontal branch stars. The second channel is envelope ejection channel, in which a star ejects its envelope near the tip of FGB if the binding energy of the envelope becomes positive, and the remnant star becomes a hot subdwarf. Hot subdwarf stars may form in metal-rich old stellar populations from the envelope ejection channel and contribute to the far-UV excess in early-type galaxies.