A spectroscopic study of mass outflows in the interacting binary RY scuti

The massive interacting binary RY Scuti is an important representative of an active mass-transferring system that is changing before our eyes and which may be an example of the formation of a Wolf-Rayet star through tidal stripping. Utilizing new and previously published spectra, we present examples of how a number of illustrative absorption and emission features vary during the binary orbit. We identify spectral features associated with each component, calculate a new, double-lined spectroscopic binary orbit, and find masses of 7.1 ± 1.2 M_⊙ for the bright supergiant and 30.0 ± 2.1 M _⊙ for the hidden massive companion. Through tomographic reconstruction of the component spectra from the composite spectra, we confirm the O9.7 Ibpe spectral class of the bright supergiant and discover a B0.5 I spectrum associated with the hidden massive companion; however, we suggest that the latter is actually the spectrum of the photosphere of the accretion torus immediately surrounding the massive companion. We describe the complex nature of the mass-loss flows from the system in the context of recent hydrodynamical models for β Lyr, leading us to conclude RY Scuti has matter leaving the system in two ways: (1) a bipolar outflow from winds generated by the hidden massive companion, and (2) an outflow from the bright O9.7 Ibpe supergiant in the region near the L2 point to fill out a large, dense circumbinary disk. This circumbinary disk (radius ≈1 AU) may feed the surrounding double-toroidal nebula (radius ≈2000 AU).