Determination of Primordial Metallicity and Mixing in the Type II‐P Supernova 1993W

We present the results of a large grid of synthetic spectra and compare themto early spectroscopic observations of SN 1993W. This supernova was discoveredclose to its explosion date and at a recession velocity of 5400 km/s is locatedin the Hubble flow. We focus here on two early spectra that were obtainedapproximately 5 and 9 days after explosion. We parameterize the outer supernovaenvelope as a power-law density profile in homologous expansion. In order toextract information on the value of the parameters a large number of models wasrequired. We show that very early spectra combined with detailed models canprovide constraints on the value of the power law index, the ratio of hydrogento helium in the surface of the progenitor, the progenitor metallicity and theamount of radioactive nickel mixed into the outer envelope of the supernova.The spectral fits reproduce the observed spectra exceedingly well. The spectralresults combined with the early photometry predict that the explosion date was4.7 \pm 0.7 days before the first spectrum was obtained. The ability to obtainthe metallicity from early spectra make SN IIP attractive probes of chemicalevolution in the universe and by showing that we have the ability to pin downthe parameters of the progenitor and mixing during the supernova explosion, itis likely to make SN IIP useful cosmological distance indicators which are atthe same time complementary to SNe Ia.Comment: 30 pages, 4 Tables, 16 Figures (some color), submitted to Ap