SULFUR CHEMISTRY IN THE ENVELOPE OF VY CANIS MAJORIS: DETAILED ANALYSIS OF SO AND SO2 EMISSION

Detailed radiative transfer modeling has been carried out for SO2 and SO originating in the envelope of the O-rich supergiant star VY Canis Majoris (VY CMa). A total of 27 transitions of SO2 and 7 transitions of SO lying in the energy range 3.0-138.2 cm(-1) were analyzed using a new non-LTE radiative transfer code that incorporates non-spherical geometries. The spectra were primarily obtained from the Arizona Radio Observatory (ARO) 1 mm spectral survey of VY CMa, conducted with the Submillimeter Telescope; additional lines were measured with the ARO 12 m antenna at 2 and 3 mm. SO2 and SO were found to arise from five distinct outflows within the envelope, four which are asymmetric with respect to the star. Three flows arise from high-velocity red-shifted material, one from a blue-shifted wind, and the final from a classic spherical expansion. In the spherical component, the peak fractional abundance, relative to H-2, of both molecules is f similar to 2.5 x 10(-7) at r similar to 25 R-*, and steadily decreases outward. SO2 appears to be a parent molecule, formed near the stellar photosphere. In the asymmetric outflows, both SO and SO2 are more prominent at large stellar radii in dense (10(6)-10(7) cm(-3)), clumpy material, achieving their maximum abundance between 200 and 600 R-* with f similar to 3.0 x 10(-8)-1.5 x 10(-7). These results suggest that in the collimated outflows, both species are either produced by shock chemistry or are remnant inner shell material swept up in the high-velocity winds.