Keck LWS images of the compact nebula around RY Scuti in the thermal infrared

We report new 3 to 20 mum Keck Telescope images of the massive eclipsing bi nary RY Scuti with similar to0." 25 spatial resolution. These images show c omplex structure near the diffraction limit of the 10 m telescope in a nebu la less than 2" across. The limb-brightened structure is consistent with op tically thin emission from a circumstellar torus. At 3 to 5 mum, the extend ed emission is predominantly scattered photospheric light from the central stars. The 8.9, 11.7, 12.5, and 18.7 mum images are dominated by thermal em ission from warm carbon and silicate dust in the outer regions of the torus . The new observations are consistent with the geometric models previously proposed by Gehrz et al. and Smith et al. to explain the structures observe d in the circumstellar environment of RY Scuti. For example, the inside of the torus is ionized by the central star and shows strong emission from [Ne II] at 12.8 mum. Double-ring structure similar to that seen in Hubble Spac e Telescope images is partly resolved at the limb-brightened edges of the t orus in the new mid-infrared continuum images, and the new IR images are co nsistent with two parallel dust rings adjacent to the ionized gas rings and farther from the star. The new mid-infrared images at 8.9, 11.7, and 12.5 urn show faint emission from a thin disk outside the previously detected to rus. We estimate a dust mass in the torus of 1.4 x 10(-6) M-circle dot and a neon abundance in the ionized gas of n(Ne)/n(H) greater than or similar t o 1.77 x 10(-4) from the 12.8 mum [Ne II] emission.