RY Scuti is an eclipsing binary in the constellation of Scutum. It consists of a massive central star with an accretion disc and a blue supergiant donor. It is surrounded by a dusty and an ionised torus.
Observational history RY Scuti was first observed between 1886 at Bonn Observatory in the Southern Durchmusterung with the designation BD-12 5045. It was initially classified as a B[e] star in 1925. It was later added to the General Catalogue of Variable Stars between 1948 and 1952, where it was designated RY Scuti.
Star system
Massive component The central star is surrounded by a hot, optically thick accretion disc created due to roche lobe overflow (RLOF) from the orbiting supergiant. Once it has stopped accreting, the surrounding disc might become optically thin, making it more visible.
Spectral classification Due to its shallow SiIII, OII and NII lines, it was initially estimated to have a spectral type of B2 and later as B0.5 I due to its absorption spectrum's similarity with that of HD 185859. However, the luminosity-sensitive lines present are much stronger than what is typically observed, indicating that they originate from low-density plasma and therefore most likely apply to the surrounding accretion disc rather than the star itself. Instead, the star is more likely to be of spectral type O7 due to its high effective temperature.
Supergiant The supergiant component is less massive but more luminous and larger than the central star. Its high abundance in neon, sulphur and iron indicates that large portions of its outer envelope have been stripped away due to RLOF, leaving hydrogen-poor material exposed.
Supernova Once the massive component has accreted all the material gained from RLOF, it is expected to become a B[e] supergiant. If it has accreted the entire outer envelope of its companion, the supergiant is expected to explode in a type Ib/c supernova or otherwise as a type IIb supernova.
Nebula RY Scuti is surrounded by a nebula which consists of a dusty and an ionised torus. The ionised torus is likely driven by episodic ejections and is expanding nonuniformly at a mean rate of 10 mas yr-1, indicating that the ejection that caused it took place between 1877 and 1885. Evidence of photometric variability during the time period indicates that one or both of the components in the system underwent an outburst similar to S Doradus. The rate of expansion of the dusty torus indicates that it formed between 1718 and 1790. They are likely to have been shaped by the massive component's accretion disc as they are clearly separated, which likely means that they are not hydrodynamically interacting, which would mean that a former large disc couldn't have shaped them.
References
