Evolutionary Models for Helium Giant Stars as Type Ibn Supernova Progenitors.

Among Type I supernovae, which show no evidence for hydrogen lines in spectra, Type Ib/c supernovae lack of strong Si absorption lines and are involved with massive progenitors. While strong helium absorption lines are present in Type Ib supernovae, narrow helium emission lines also can appear in some Type Ib that are often called Type Ibn supernovae (SNe Ibn). We consider helium giant stars as a promising progenitor candidate for SN Ibn and suggest the evolutionary scenario through binary systems using MESA code. In our models the range of primary mass is 11 - 20 solar mass, mass ratio is 0.5 - 0.9, and initial period is 1.5 / 1.7 / 2.0 / 2.5 / 3.0 day. In particular, we find that the evolution of the secondary star can overtake the primary through mass transfer from the secondary to the primary, which is so-called 'reverse case B' mass transfer. In such systems the secondary star may undergo a supernova explosion earlier than the primary star. In this case, the primary star evolves towards a single helium giant to become a SN Ibn progenitor. These cases are more frequent in relatively low initial primary mass.