2002MNRAS.336...91B

Photometric and spectroscopic observations of the peculiar Type Ib supernova 1991D are presented. SN 1991D was exceptionally bright for a Type Ib supernova. The He i lines were rather weak and the velocity at the photosphere as a function of time was unusually low. Comparison of the observed and synthetic spectra indicates that either hydrogen was ejected with a minimum velocity of 12000 km s ^–1 or the spectrum contained features caused by lines of Nei. Light curve modelling suggests that the progenitor probably had a very large radius (∼10¹⁴ cm) and that a considerable amount of ⁵⁶ Ni was synthesized during the explosion (∼0.7 M_☉). We suggest a progenitor model of SN 1991D that involves a binary system.