SUALOCIN (Alpha Delphini). Stars can come by their names in strange ways. Moreover, there is a distinct lack of consistency between naming and brightness, second magnitude Gamma Cassiopeia having no proper name and the two brighter stars in Delphinus, the Dolphin, though both of fourth magnitude, both honored with such names. If they had not been in such a jewel-like constellation, they probably would have been ignored. The mysterious names "Sualocin" and its partner "Rotanev" appeared 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 are the reversed Latinized names of the assistant to the observatory's astronomer Giuseppe Piazzi, Nicolaus Venator, so honoring him. Though at bright fourth magnitude (3.77) slightly dimmer than Rotanev, Sualocin received the constellation's Alpha designation from Bayer. This class B (B9) star, just over the edge from class A, has a surface temperature of 11,000 Kelvin. Like most B stars, it is spinning rapidly, 160 kilometers per second at its equator (70 times faster than the Sun). Its status is somewhat uncertain, some observers calling it a hydrogen-fusing main sequence star, others a subgiant that might just be starting to evolve. At a distance of 240 light years, the star appears to have a luminosity 195 times that of the Sun. 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, revealing it to be a class A star rather similar to Sirius. The principal component is therefore a bit less bright, about 175 times solar. The two orbit each other with a period of 17 years at an average separation of about 12 astronomical units, a bit farther than Saturn is from the Sun, the total mass found from the orbit to be 5.8 times solar, most of (over 3 solar masses) in the main component. Since the brighter star will die first as a dim white dwarf, the system may someday appear much as Sirius (with its white dwarf companion) does today.
Written by Jim Kaler. Return to STARS.