USING SN-1987A LIGHT ECHOES TO DETERMINE MASS-LOSS FROM THE PROGENITOR

We have monitored the many light echoes seen near SN 1987A to find how the SN progenitor influenced its preexplosion environment. There is a smooth distribution of light dimming from radii 3"-10", consistent with an echo from the mass lost at a constant rate from a red supergiant atmosphere. This flow terminates in two shocks (the smaller, bow-shaped echo and the oval-shaped echo described herein), the larger containing 12 times the mass of the flow. The total mass in all these structures (assuming spherical symmetry) is 4.5 M., assuming Mgas/Mdust = 1000 and a grain model favored by our data (50 nm radius graphite spheres). The progenitor needed almost-equal-to 10(6) yr to create these structures, assuming a constant mass loss at velocity 15 km s-1. The dust in this region is small-grained (mostly radii < 70 nm) and isotropically scattering (g < 0.2). Interaction between the progenitor blue supergiant and red supergiant winds is complex, but are likely contained within a 1.5 pc diameter, roughly spherical structure. We have also discovered a fourth star in the Sanduleak -69-degrees-202 system, 2" southwest of the SN (P. A. = 243-degrees).