Alpha Delphini is a multiple star in the constellation Delphinus, with a combined magnitude of 3.77 (slightly dimmer than β Del). α and β Del were given the name mysterious names "Sualocin" and "Rotanev" in the Palermo star catalogue of 1814. A bit of detective work by the nineteenth century English astronomer Thomas Webb finally disclosed that the stars have the reversed Latinized name - Nicolaus Venator - of Niccolo Cacciatore, the assistant to the observatory's astronomer Giuseppe Piazzi.
Properties
Sualocin is a class B9 V star, with a surface temperature of 11,000 K. Like most B stars, it is spinning rapidly, 160 km/sec at its equator. At a distance of 240 light years, the star appears to have a luminosity 195 times the Sun's. It has been known for some time, however, that Sualocin has a close companion a fraction of a second of arc away. Modern measurements with the Hipparcos satellite show the companion to be about a tenth the brightness of the principal star (magnitude 6.4, versus 3.9), revealing it to be a class A star rather similar to Sirius. The principal component is therefore a bit less luminous, about 175 times solar. The two orbit each other with a period of 17 years, at an average separation of about 12 AU, a bit farther than Saturn is from the Sun. The total mass found from the orbit is 5.8 suns, most of it (over 3 solar masses) in the main component.
Sualocin's evolutionary status is somewhat uncertain; it may be a hydrogen-fusing main sequence star, or a subgiant just starting to evolve off the main sequence. Since the brighter star will evolve first to a dim white dwarf, the system may someday appear much as Sirius does today.
In total, α Del has seven components: A and Aa (the physical binary), and B, C, D, E, and F, which are optical and have no physical association with A and Aa.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]