A hybrid envelope-stripping mechanism for massive stars from supernova nebular spectroscopy

The final steps of the evolution of massive stars leading to a supernova explosion, in particular the mass-loss mechanism, is an important open problem in astrophysics. Stripped-envelope supernovae (SESNe) are explosions of massive stars where a large amount of the outer envelope has been stripped away before the explosion: types IIb, Ib and Ic in order of increasing degree of envelope stripping ^1–3 . In this work, an analysis of late-time nebular spectra of SESNe is presented. The results show that the progenitors of SNe IIb and Ib are indistinguishable except for the residual amount of the H-rich envelope. The progenitors of SNe Ic are distinctly different in the nature of the carbon–oxygen (C+O) core, which is interpreted to be more massive than in SNe IIb and Ib. These findings strongly suggest that different mechanisms are responsible for the removal of the outer H-rich envelope and the deeper He-rich layer.