RY SCUTI - INFRARED AND RADIO OBSERVATIONS OF THE MASS-LOSS WIND OF AMASSIVE BINARY STAR SYSTEM

We report infrared (IR) imaging, IR photometry, IR spectroscopy, optic al/IR photopolarimetry, and VLA radio observations of the peculiar bin ary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, ''overcontact'' binary system. The binary star (0.4 3 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximate to 3 x 10(16) cm (2000 AU) that emits stro ngly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 mu m forbidden-line emissio n from [Ne II]; the outside of the disk emits thermal radiation from s ilicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic arom atic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physic al properties of the disk. The mean radius of the ionized gas toroid i s approximate to 1.3 x 10(16) cm (870 AU), and the mean radius of the dust toroid is approximate to 2.2 x 10(16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scatterin g from hot gas close to the central binary. We conclude that neon in t he nebula is overabundant with respect to hydrogen and helium by a fac tor of between 1.6 and 10. Our IR/radio image data suggest that the ci rcumstellar disk is part of an extensive radiation driven mass-loss ou tflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust format ion in the circumstellar ejecta of very hot stars must occur in region s that are shielded from the hard radiation field.