Optical Spectroscopy of the Somewhat Peculiar Type IIb Supernova 2001ig

Here we present previously unpublished optical spectra of supernova (SN) 2001ig, a Type IIb SN, from about a week after explosion until nearly one year later.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 similar to 1.15 M(circle dot) of material, most of which (by mass) is in the form of oxygen, with similar to 0.13 M(circle dot) of (56)Ni and essentially no hydrogen.