The unusual supernova SN1993J in the galaxy M81

SUPERNOVA 1993J in the galaxy M81 is the second-brightest type II supernova observed this century, surpassed only by SN1987A in the Large Magellanic Cloud. Here we report the evolution of the photometric and spectral properties of SN1993J for the first 50 days following its discovery. The behaviour of this supernova is unusual, showing features typical of type II supernovae near the initial maximum, but with the strong helium lines characteristic of type Ib supernovae at later times. This implies that the progenitor star had an unusually thin hydrogen envelope (compared to normal type II progenitors), suggesting that significant mass loss had taken place before the explosion. Application of an expanding photosphere model1 to our data provides an estimate of the distance to the supernova of 2.6 +/- 0.4 Mpc, broadly consistent with the distance to M81 determined using Cepheid variable stars2. Supernova models that more closely match the atypical spectral features of SN1993J may change the inferred distance, and should provide better constraints on the structure of the progenitor

THE EXPANDING PHOTOSPHERE METHOD APPLIED TO SN-1992AM AT CZ=14600KM-S

Artículo de publicación ISIWe present photometry and spectroscopy of SN 1992am for five months following its discovery by the Calan/CTIO SN search. These data show SN 1992am to be type II-P, displaying hydrogen in its spectrum and the typical shoulder in its light curve. The photometric data and the distance from our own analysis are used to construct the supernova's bolometric light curve. Using the bolometric light curve, we estimate SN 1992am ejected approximately 0.30. M. of Ni-56, an amount four times larger than that of other well studied SNe II. SN 1992am's; host galaxy lies at a redshift of cz = 14 600 km s-1, making it one of the most distant SNe II discovered, and an important application of the Expanding Photosphere Method. Since z = 0.05 is large enough for redshift-dependent effects to matter, we develop the technique to derive luminosity distances with the Expanding Photosphere Method at any redshift. and apply this method to SN 1992am. The derived distance, D = 180(+30/-25) Mpc, is independent of all other rungs in the extragalactic distance ladder. The redshift of SN 1992am's host galaxy is sufficiently large that uncertainties due to perturbations in the smooth Hubble flow should be smaller than 10%. The Hubble ratio derived from the distance and redshift of this single object is H-0 = 81(+17/-15) km s-1 Mpc-1. In the future, with more of these distant objects, we hope to establish an independent and statistically robust estimate of H-0 based solely on type II supernovae