2015ApJ...809..131K

In several recent observational studies of Type Ib/c supernovae (SNe Ib/c), the inferred ejecta masses have a peak value of 2.0-4.0, in favor of the binary scenario for their progenitors rather than the Wolf-Rayet star scenario. To investigate the observational properties of relatively low-mass helium stars in binary systems as possible SN Ib/c progenitors, we constructed atmospheric models with the non-LTE radiative transfer code CMFGEN, using binary star evolution models. We find that these helium stars can be characterized by relatively narrow helium emission lines if the mass-loss rate during the final evolutionary phase is significantly enhanced as implied by many SN Ib/c observations. The optical brightness of helium star progenitors can be meaningfully enhanced with a strong wind for stars with, but is hardly affected or slightly weakened for relatively low-mass stars with, compared to the simple estimate using blackbody approximation. We further confirm the previous suggestion that the optical brightness would be generally higher for a less massive SN Ib/c progenitor. In good agreement with previous studies, our results indicate that the optical magnitudes and colors of the recently detected progenitor of the SN Ib iPTF13bvn can be well explained by a binary progenitor with a final helium star mass of about 3.0-4.4.