Radiative-transfer models for supernovae IIb/Ib/Ic from binary-star progenitors

We present 1D non-local thermodynamic equilibrium time-dependent radiative-transfer simulations for supernovae (SNe) of Type IIb, Ib, and Ic that result from the terminal explosion of themass donor in a close-binary system. Here, we select three ejecta with a total kinetic energy of ≈1.2 × 10⁵¹ erg, but characterized by different ejecta masses (2-5 M⊙), composition, and chemical mixing. The Type IIb/Ib models correspond to the progenitors that have retained their He-rich shell at the time of explosion. The Type Ic model arises from a progenitor that has lost its helium shell, but retains 0.32 M⊙ of helium in a CO-rich core of 5.11 M⊙.We discuss their photometric and spectroscopic properties during the first 2-3 months after explosion, and connect these to their progenitor and ejecta properties including chemical stratification. For these three models, Arnett's rule overestimates the ⁵⁶Ni mass by ≈ 50 per cent while the procedure of Katz et al., based on an energy argument, yields a more reliable estimate. The presence of strong C I lines around 9000Å prior to maximum is an indicator that the pre-SN star was underabundant in helium. As noted by others, the 1.08Μm feature is a complex blend of C I, MgII, and He I lines, which makes the identification of He uncertain in SNe Ibc unless other He I lines can be identified. Our models show little scatter in (V - R) colour 10 d after R-band maximum. We also address a number of radiative transfer properties of SNe Ibc, including the notion of a photosphere, the inference of a representative ejecta expansion rate, spectrum formation, blackbody fits and 'correction factors'.