The interstellar medium towards SN 1993J in M81

Summary

Introduction

Supernovae are important for the study of several astrophysical problems – nuclear processing in stellar interiors, distance scale determinations, and the chemical enrichment of the interstellar medium have all been explored. Additionally, they may be used as background probes of interstellar gas by studying, for example, NaI and CaII lines, sampling the gas in the host galaxy, the Milky Way halo gas, and any intervening intergalactic gas. SN 1987A allowed the detailed study of gas towards and within the LMC to a distance D ≃ 0.05 Mpc (Vidal-Madjar et al. 1987, de Boer et al. 1987). With the unusually bright SN 1993J in M81 it is now possible to extend the search for interstellar/intergalactic absorptions beyond the local group of galaxies, out to the distance of the M81 group at a distance of D~3.25 Mpc. In this paper we present a preliminary study of high resolution optical interstellar spectra towards SN 1993J. The observations are described in section 2. The origin of the absorption lines, which fall into three distinct groups are discussed in section 3.

Observations

The observations of SN 1993J were obtained during the nights 1993 April 4–8, using the Utrecht Echelle Spectrograph on the William Herschel Telescope at the Observatorio del Roque de los Muchachos, La Palma.