The First chemical enrichment in the universe and the formation of hyper metal-poor stars

Iwamoto, Nobuyuki  ; Umeda, Hideyuki*; Tominaga, Nozomu*; Nomoto, Kenichi*; Maeda, Keiichi*

The recent discovery of a hyper-metal-poor (HMP) star, with a metallicity Fe/H smaller than 1/100,000 of the solar ratio, together with one earlier HMP star, has raised a challenging question whether these HMP stars are the actual first-generation, low-mass stars of the universe. We argue that these HMP stars are the second-generation stars formed from gases that were chemically enriched by the first-generation supernovae. The key to this solution is the very unusual abundance patterns of these HMP stars and the similarities and differences between them. We can reproduce these abundance features with core-collapse "faint" supernova models that include extensive matter mixing and fallback during explosions.