Observational Properties of Type Ib/c Supernova Progenitors in Binary Systems

TL;DR

This study models binary star progenitors of Type Ib/c supernovae, showing that low-mass helium stars with enhanced mass loss can explain observed supernova properties and progenitor brightness.

Contribution

It provides detailed atmospheric models of binary helium star progenitors, linking their properties to observed supernova ejecta masses and brightness.

Findings

Helium stars with high mass-loss rates show narrow helium emission lines.

Progenitor brightness increases with wind strength for masses above 4.4 M_sun.

Progenitor brightness is higher for less massive SN Ib/c progenitors.

Abstract

In several recent observational studies on Type Ib/c supernovae (SNe Ib/c), the inferred ejecta masses have a peak value of 2.0 -- 4.0 $M_\odot$, 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 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 $M \gtrsim 4.4 M_\odot$, but hardly affected or slightly weakened for relatively low-mass of $\sim 3.0 M_\odot$, 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 $M_\odot$.