THE TYPE-IA SUPERNOVA 1989B IN NGC-3627 (M66)

We report extensive optical photometry and spectroscopy of the Type Ia supernova 1989B. Maximum light in B occurred approximately seven days after discovery on JD 2447565.3 +/- 1.0 (1989 February 7.8 +/- 1.0) a t a magnitude of 12.34 +/- 0.05. The UBV light curves of this supernov a were very similar to those of other well observed Type Ia events suc h as SN 1981B and SN 1980N. From a comparison of the UBVRIJHK photomet ry, we derive an extinction for SN 1989B of E(B-V) = 0.37 +/- 0.03 mag s relative to the unobscured Type Ia SN 1980N. The properties of the d ust responsible for the reddening of SN 19898 appear to have been simi lar to those of normal dust in the Milky Way. In particular, we find n o evidence for an unusually low value of the ratio of the total to sel ective absorption. We derive a distance modulus of Delta mu(0) = -1.62 +/- 0.03 mag relative to the Type Ia SN 1980N. We present optical spe ctra which provide essentially continuous coverage of the spectral evo lution of SN 1989B over the first month following B maximum. These dat a show the transition from the maximum-light spectrum, in which lines of elements such as Ca, Si, S, Mg, and O are most prominent, to the Fe -dominated spectrum observed a few weeks after maximum. This transitio n occurred quite smoothly over a two-week period following B maximum. Comparison of the spectra of SN 1989B with data for two other well. ob served Type Ia supernovae-1981B and 1986G-reveals subtle differences i n the relative strengths of the S II and Si II absorption lines at max imum light. However, these differences disappeared within a week or so after maximum with the onset of the Fe-dominated phase.