Using SN 1987A light echoes to determine mass loss from the progenitor

Abstract

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_sun_, assuming M_gas_/M_dust_ = 1000 and a grain model favored by our data (50 nm radius graphite spheres). The progenitor needed ~ 10^6^ yr to create these structures, assuming a constant mass loss at velocity I5 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^deg^202 system, 2" southwest of the SN (P.A. = 243^deg^).