Near field cosmology with binary, high mass IMF, and hierarchical galaxy formation

Abstract

Extremely metal‐poor (EMP) stars in the Galactic halo are the remaining survivors of the early generations of stars. Their surface element abundances are signature of the nucleosynthesis in the first and second generation of stars. From comparison between the observationsof EMP stars and calculations of stellar evolution, it is suggested that typical mass of EMP stars are much higher than more metal‐rich one and the majority of observed EMP stars are formed in binary systems. I review the effect of binarity and difference of initial mass function on the EMP stars and chemical evolution of galaxy. We calculate chemical enrichment history in the context of hierarchical Galaxy formation with high mass IMF and binary contribution. We compare resultant abundance distributions with observations. Additionally, I discuss the origin of the most metal‐deficient stars known to date.