THE ASTRONOMICAL JOURNAL    VOLUME 107, NUMBER 3, PAGE 1022          MARCH 1994

            UBVRI PHOTOMETRY OF SN 1993J IN M81: THE FIRST 120 DAYS

                              MICHAEL W. RICHMOND

          Department of Astrophysical Sciences, Princeton University,
                          Princeton, New Jersey 08544
                 Electronic mail: richmond@astro.princeton.edu
 
           RICHARD R. TREFFERS, ALEXEI V. FILIPPENKO, AND YOUNG PAIK

 Department of Astronomy, University of California, Berkeley, California 94720
    Electronic mail: treffer@bkyast.berkeley.edu, alex@bkyast.berkeley.edu,
                           ypaik@goofy.berkeley.edu

                               BRUNO LEIBUNDGUT

         European Southern Observatory, Karl-Schwarzschild-Strasse 2,
                     D-8046 Garching bei Muenchen, Germany
                       Electronic mail: bleibund@eso.org

                       ERIC SCHULMAN AND CAROLINE V. COX

Department of Astronomy, University of Michigan, Ann Arbor, Michigan 48109-1090
     Electronic mail: eric@astro.lsa.umich.edu, cvcox@astro.lsa.umich.edu

                                   ABSTRACT

    We present photometry of SN 1993J in M81 (NGC 3031) in the
    Johnson-Cousins UBVRI system, starting within three days of the
    probable time of explosion and ending 120 days later.  The reddening
    along the line of sight to this supernova is uncertain -- there is
    evidence for small [E(B-V) ~ 0.08 mag] and moderate [E(B-V) ~ 0.32 mag]
    values.  For each value, we correct the observed fluxes for extinction
    and calculate the evolution of the sum of all optical flux, which
    contains roughly half of the supernova's total flux during the period
    of observation.  We also fit the colors to a Planck function, and
    determine the temperature and total luminosity of the supernova for each
    value of reddening.  A peculiar Type II supernova, SN 1993J gradually
    evolved spectroscopically to resemble a Type Ib in some respects. We
    compare its bolometric evolution with that of the prototypical Type Ib
    SN 1983N, and find the two to be similar.