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 12,000 km/s or the spectrum contained features caused by lines of Ne I. Light curve modelling suggests that the progenitor probably had a very large radius (~10^14 cm) and that a considerable amount of 56Ni was synthesized during the explosion (~0.7 Msolar). We suggest a progenitor model of SN 1991D that involves a binary system.
@article{arxiv.astro-ph/0205453,
title = {Exceptionally Bright Type Ib Supernova 1991D},
author = {S. Benetti and D. Branch and M. Turatto and E. Cappellaro and E. Baron and L. Zampieri and M. Della Valle and A. Pastorello},
journal= {arXiv preprint arXiv:astro-ph/0205453},
year = {2009}
}