Optical spectrum of supernova 1989 B in NGC 3627

Abstract

Spectra of SN 1989 B in NGC 3627 were recorded photographically on three nights near maximum and two nights near seven weeks from maximum. The spectrum and its evolution bears a close resemblance to a typical type Ia spectrum. The expansion velocity of the envelope decreased with time as observed in other supernovae. The velocity evolution is similar to that of SN 1981 B, but the magnitude is 10 percent smaller. Early velocities are comparable to those of SN 1986 G, but the latter evolved faster. Early spectroscopic evolution was faster than SN 1981 B, but compares well with SN 1986 G. It is proposed that the rate of spectral evolution, as judged from the epoch at which S II 545.4, 546.0 nm lines disappear and NaID, Fe II 492.4, 521.5 nm become prominent, is inversely correlated with the velocity of the envelope: faster envelopes evolve slower.