Optical Spectroscopy of the Somewhat Peculiar Type IIb Supernova 2001ig

Silverman, Jeffrey M.
Mazzali, Paolo
Chornock, Ryan
Filippenko, Alexei V.
Clocchiatti, Alejandro
Phillips, Mark M.
Ganeshalingam, Mohan
Foley, Ryan J.
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Here we present previously unpublished optical spectra of supernova (SN) 2001ig, a Type IIb SN, from about a week after explosion until nearly one year later.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.
Comment: 11 pages, 5 figures, 3 tables, submitted to PASP
Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics