Low-Resolution Spectra of the Supernova 1993J in M81

Abstract

We present the low-resolution optical spectra of supernova 1993J in M81 near to the first maximum light (1993 March 31 and April 1 in UT), near to the second maximum light (April 17–19), and after the second maximum light (May 7 and June 7). The spectra cover wavelengths of λλ4500 (or 5000)–7500 Å with a spectral resolution of 12–36 Å. Near to the first maximum light, the spectra are rather featureless with some absorption lines and bumps. The Hα line with a prominent P Cyg profile and some absorption features caused by Fe II lines and Na I D lines are seen in the spectra near to the second maximum light. We derived the expansion velocities of the supernova from these lines. From the Hα absorption line at the blue edge of the emission, we obtained radial velocities of –12000 to –13000 km s–1 while the Fe II lines show velocities of –7100 to –7600 km s–1. The spectra after the second maximum show the presence of some P Cyg profiles by He I and resemble those of type-Ib supernovae.