Po-Sheng Ou (ASIAA/NTU); Ke-Jung Chen (ASIAA); You-Hua Chu (ASIAA)
We present a systematic study of the mass loss of massive stars. Mass loss plays a vital role in the evolution of massive stars, and it is suggested to depend on metallicity. However, the total mass loss during the lifetimes of massive stars with different metallicities is still unclear. In this paper, we use 1D stellar evolution models to understand the physics of mass loss and its dependence on stellar metallicity. We consider different stellar masses and metallicities to build up a grid of ~2000 models. Stellar winds, containing hot main-sequence wind and cool supergiant wind, are the main drivers to the mass loss of massive stars in our models. Our results demonstrate the existence of a critical metallicity Zc at the absolute metallicity Z~10^-3, around which the mass loss shows dramatic behaviors. With a Z>Zc, massive stars tend to evolve into the red supergiants, then trigger a robust cold wind through dust formation. On the other hand, if Z is lower than Zc, massive stars would remain compact and evolve into the blue supergiants, in which cold wind is not active, and the mass loss is generally weak. We also propose a mechanism of red supergiant formation based on our simulations to explain the critical metallicity. We found that the iron opacity bump at the temperature of 30,000 K can trigger the inflation of supergiant envelopes. The lowest metallicity value that can drive the Ledoux instability at the iron opacity bump is defined as the critical metallicity. Besides, we also calculate feedback of mass loss, which yields momentum and energy for a 10^5 Msun star cluster with the Salpeter IMF. Our results provide realistic stellar wind feedback models, which are useful for the galaxy and ISM simulations.