SN-1993J IN M81 - OPTICAL PHOTOMETRY AND SPECTROPHOTOMETRY DURING THEFIRST 2 MONTHS

CCD photometric and spectrophotometric data on the type IIb supernova 1993J in M 81 (NGC 3031) obtained from Vainu Bappu Observatory, Kavalu r, during the first two months since the outburst are reported. The ev olution of the spectrum is described. The evolution of the velocity of P-Cygni absorption dips due to different lines is presented. The phot ospheric temperature and radius are determined using blackbody fits to BV RI JHK photometry after correcting for interstellar extinction and contribution to the band by the net line emission. The evolution of p hotospheric radius implies a density variation in the progenitor rho p roportional to r(-n) With n = 5 - 6 during the rise to the second maxi mum reducing to n = 2 soon after. These values are comparable to the c orresponding values for SN1987A. An application of the expanding photo sphere method yields a distance of 2.2 - 5.1 Mpc for the range of E(B - V) = 0.08 - 0.32, and the atmospheric dilution factor zeta = 0 - 0.4 . The distance estimates with the assumption of low reddening and low dilution as well as moderate reddening and moderate dilution are both consistent with the HST Cepheid distance to M 81 (3.6 +/- 0.3 Mpc).