THE SUPERNOVA RING REVISITED .2. DISTANCE TO THE LARGE MAGELLANIC CLOUD

I derive an upper limit to the distance to SN 1987A of D-SN < 46.77 +/- 0.76 kpc, or a distance modulus mu(SN) < 18.350 +/- 0.035. If SN 1987A lies in the plane of the Large Magellanic Cloud (LMC) and hence 500 pc in front of the LMC center, this implies mu(LMC) < 18.37 +/- 0.04. The determination rests on a new measurement of the caustics in the ionized-emission light curves of t(-) = 75.0 +/- 2.6 days and t(+) = 390.0 +/- 1.8 days combined with a recent remeasurement of the angular size of the ring by Plait et al. (1995). The new distance estimate is 11% lower than the one made using old values for the caustic times and angular size. More than half of the change is due to the new, lower values of t(+). The estimate assumes that the ring is circular. This assumption is shown to be consistent with the available data and can be subjected to a future precise test. Moreover, I have previously shown that modest deviations from circularity (eccentricities e < 0.4) affect the result by less than 1%. The upper limit to the distance modulus to M31 is mu(M31) < 24.43 +/- 0.06. If the response function of the supernova ring gas is prompt, then these upper limits become equalities.