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B. E. K. Sugerman (Space Telescope Science Institute), A. P. S. Crotts (Columbia University), S. S. Lawerence (Hofstra University), S. R. Heathcote (CTIO), W. E. Kunkel (Carnegie Inst. of Washington)
Surrounding SN 1987A is a three-ring nebula attributed to interacting stellar winds, yet no model has successfully reproduced this system. Fortunately, the supernova (SN) has provided an ideal opportunity to reconstruct the progenitor's mass-loss history through scattered-light echoes, which trace the three-dimensional (3-D) morphology of the circumstellar dust. Using PSF-matched difference imaging to study both phenomena, we have built the most complete map to date of the circumstellar environment (CSE).
The CSE is a richly-structured bipolar nebula. An outer, double-lobed ``peanut'' is a prolate shell extending 28 ly along the poles and 11 ly near the equator, but is pinched to 6 ly at the waist. Interior, a cylindrical hourglass, 1 ly in radius and 4 ly long, connects to the peanut by a thick equatorial disk. The nebulae are inclined 40\degr south and 8\degr east of the line of sight, slightly elliptical in cross section, and marginally offset west of the SN.
Echo fluxes suggest that between the hourglass and bipolar lobes: the gas density drops from 1--3 cm-3 to \gtrsim 0.03 cm-3; the maximum dust-grain size increases from ~0.2\micron to 2\micron; and the silicate:carbonaceous dust ratio decreases. The nebulae have a total mass of ~ 1.7 M\sun, suggesting a red-supergiant mass loss of 5\times10-6 M\sun yr-1.
We compare these results to current formation models, and propose the progenitor evolved through two ``blue-loops,'' during which a fast, low-density blue supergiant wind interacted with previously-ejected, slow, high-density red supergiant material. We study the 3-D geometry of the three rings, suggesting the northern and southern rings are located 1.3 and 1.0 ly from the SN, while the equatorial ring is elliptical (b/a\lesssim 0.98), and spatially offset in the same direction as the hourglass.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.