Here we present previously unpublished optical spectra of supernova (SN) 2001ig, a Type IIb SN, from about a week after explosion until nearly one year later. The earliest spectrum consists of only a few broad absorption features, but soon more common Type II SN features including hydrogen P-Cygni profiles and helium absorption become apparent. At later times, as the H features fade and the He I absorption becomes more prominent, we observe the SN to transition from a Type II to a Type Ib. Finally, observations after 250 days past explosion show a nebular-phase SN spectrum with one of the largest magnesium to oxygen intensity ratios ever seen. Additionally, we present models of the late-time spectra which indicate that the inner ejecta consist of ~1.15 M_sun of material, most of which (by mass) is in the form of oxygen, with ~0.13 M_sun of Ni-56 and essentially no hydrogen.
@article{arxiv.0903.4179,
title = {Optical Spectroscopy of the Somewhat Peculiar Type IIb Supernova 2001ig},
author = {Jeffrey M. Silverman and Paolo Mazzali and Ryan Chornock and Alexei V. Filippenko and Alejandro Clocchiatti and Mark M. Phillips and Mohan Ganeshalingam and Ryan J. Foley},
journal= {arXiv preprint arXiv:0903.4179},
year = {2015}
}