First Stars -- Type Ib Supernovae Connection

The very peculiar abundance patterns observed in extremely metal-poor (EMP) stars can not be explained by ordinary supernova nucleosynthesis but can be well-reproduced by nucleosynthesis in hyper-energetic and hyper-aspherical explosions, i.e., Hypernovae (HNe). Previously, such HNe have been observed only as Type Ic supernovae. Here, we examine the properties of recent Type Ib supernovae (SNe Ib). In particular, SN Ib 2008D associated with the luminous X-ray transient 080109 is found to be a more energetic explosion than normal core-collapse supernovae. We estimate that the progenitor's main sequence mass is 20--25 M_sun and a kinetic energy of explosion is ~ 6 x 10^{51} erg. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. Such energetic SNe Ib can make important contribution to the chemical enrichment in the early Universe.