OPTICAL-SPECTRA OF SN 1993J DURING THE FIRST 500 DAYS

Low-dispersion optical spectra of SN 1993J taken at the MDM Observatory during the first 500 days are presented. These data include nightly spectra during the first week and individual spectra taken at 1, 6, 10, 11, 12, and 16 months after explosion. The spectra document the supernova's transformation from a SN II to SN Ib and the transition into the nebular phase. Spectra taken 1993 March 31-April 7 resolve some discrepancies in reported spectral features through a comparison of MDM data with other published datasets. Early-time expansion velocities for Hα, Hβ, and He I using absorption minima of P-Cygni features are reported along with photospheric temperatures determined through the fitting of reddened blackbody curves. Spectra covering the time period of 300 to 500 days after explosion show the reemergence of broad Hα emission (FWZI=2×104 km s-1) with a peak flux level of 3.3×10-16 erg s-1 cm-2 Å-1 in 1994 June. Late-time spectra also reveal the reappearance of narrow Hα emission after day 300. This emission is likely due to faint H II region emission near the SN 1993J site. © 1995 American Astronomical Society.