SN-1987A IN THE LMC .3. UBVRI PHOTOMETRY AT CERRO-TOLOLO

We present UBVRI photometry of supernova 1987A in the Large Magellanic Cloud for 813 days since outburst This photometry is based on an improved calibration of the photometry of the local standard stars and a careful analysis of the transformation from the natural system to the standard photometric system. Compared to the uniform exponential decline seen in UBVRI between days 125 and 400, SN 1987A began to fade more rapidly in all colors starting around day 500, at the time a strong thermal component appeared. Comparison with photometry of SN 1987A taken at other observatories shows that while the internal accuracy of any measurement approaches 0.01 mag, the systematic differences between UBVRI photometry obtained at different sites can be as large as 0.4 mag, due to the nonstellar nature of the spectral energy distribution of SN 1987A.