The Last Gasps of VY Canis Majoris: Aperture Synthesis and Adaptive Optics Imagery

We present new observations of the red supergiant VY CMa at 1.25 micron, 1.65micron, 2.26 micron, 3.08 micron and 4.8 micron. Two complementaryobservational techniques were utilized: non-redundant aperture masking on the10-m Keck-I telescope yielding images of the innermost regions at unprecedentedresolution, and adaptive optics imaging on the ESO 3.6-m telescope at La Sillaattaining extremely high (~10^5) peak-to-noise dynamic range over a wide field.For the first time the inner dust shell has been resolved in the near-infraredto reveal a one-sided extension of circumstellar emission within 0.1" (~15R_star) of the star. The line-of-sight optical depths of the circumstellar dustshell at 1.65 micron, 2.26 micron, and 3.08 micron have been estimated to be1.86 +/- 0.42, 0.85 +/- 0.20, and 0.44 +/- 0.11. These new results allow thebolometric luminosity of VY~CMa to be estimated independent of the dust shellgeometry, yielding L_star ~ 2x10^5 L_sun. A variety of dust condensations,including a large scattering plume and a bow-shaped dust feature, were observedin the faint, extended nebula up to 4" from the central source. While theorigin of the nebulous plume remains uncertain, a geometrical model isdeveloped assuming the plume is produced by radially-driven dust grains formingat a rotating flow insertion point with a rotational period between 1200-4200years, which is perhaps the stellar rotational period or the orbital period ofan unseen companion.Comment: 25 pages total with 1 table and 5 figures. Accepted by Astrophysical Journal (to appear in February 1999