A spectrographic study of the interacting eclipsing binary RY Scuti: an episode in the rapid mass loss stage or a protoplanetary nebula?

RY Scuti, the 11-day [Fe III] eclipsing binary, has been reinvestigated on the basis of spectrographic material obtained in Chile at the European Southern Observatory, La Silla, and at the Cerro Tololo Interamerican Observatory, covering the spectral regions 3400–5150 ˚ and 5700–6700 ˚ Ultraviolet IUE observations were also analyzed. The spectrum of RY Sct is very complex and peculiar, being characterized by several sets of emission as well as absorption features. Among the emission features, there is a set of lines that are characteristic of planetary nebulae. The system is found to be formed by a B0V component and a companion that appears to be surrounded by an opaque envelope that emits in He II λ4686. In the circumbinary envelope we can distinguish: (a) a region of diluted radiation that suggests a velocity of ∼− 178 km s −1 ; (b) regions of formation of the resonance lines of Si IV and C IV in the IUE UV, characterized by velocities of −1200 and −600 km s −1 ; (c) regions that give rise to the “nebular spectrum” and suggest that there is a triple nebulosity surrounding the system with Ne probably larger than 10 4 cm −3 , Te ∼ 15–20,000 K and velocities of −18, +9 and +48 km s −1 , respectively.