THE TYPE IA SUPERNOVA 1986G IN NGC 5128 : OPTICAL PHOTOMETRY AND SPECTRA.

Optical light curves and spectra of the Type Ia supernova 1986G in NGC 5128 (Centaurus A) are presented. Although the spectral evolution closely resembled that of the more common "slower" photometric classes of Type Ia supernovae, subtle differences in the maximum-light spectra were detected. The expansion velocity of the photosphere of SN 1986G decreased rapidly at early phases. SN 1986G appears to have been heavily obscured by the dust lane of NGC 5128. This circumstances accounts for the strong interstellar-absorption lines of Ca II H and K and Na I D observed in the spectra as well as for features that the authors identify with the diffuse interstellar bands. SN 1986G provides graphic confirmation of the existence of intrinsic differences in the optical light curves and spectroscopic properties of Type Ia supernovae. Consequently, these objects must be used with considerable caution as cosmological standard candles. The authors derive a relative distance of DNGC 5128/DNGC 5055 = 0.39±0.04.