We thank Massimo Turatto for sending spectra of SN 1997D. We are grateful to Ken Nomoto, Bruno Leibundgut, Peter Lundqvist, and Wolfgang Hillebrandt for discussions and comments. N.Ch. thanks Bruno Leibundgut for hospitality at ESO and V.U. thanks Wolfgang Hillebrandt and Ewald Müller for hospitality at MPA. This work was supported in part by the RFBR (project 98-02-16404), the INTAS-RFBR (project 95-0832), and the ISTC (project 97-370).
© European Southern Observatory (ESO) 2000
Online publication: February 9, 2000