PSI VEL (Psi Velorum). Almost lost among the vast number of stars of huge Argo (formally, Argo Navis, the Ship of the Argonauts), bright-fourth magnitude (3.60) Psi Velorum recommends itself three ways. First, it's the most northerly star of the classic outline of Vela the Sails (the other parts of Argo being Puppis, the Stern, and Carina, the Keel), lying just barely to the south of the dim modern constellation Antlia (the Air Pump). At a distance of only 61 light years, it's also one of the closest of Vela's (for that matter Argo's) classic stars. It's also a very close orbiting double that consists of a pair of warm class F stars (traditionally given as F3 and F0 subgiants, sometimes as F2 subgiant plus F0 hydrogen-fusing dwarf, but see below). As seen from Earth separated by under a second of arc, the two go around each other every 33.95 years at an average physical separation of 16.0 Astronomical Units, a fairly high eccentricity taking them between 9 and 23 AU apart. They were last closest together in 2003, and will be again in 2037. The orbital parameters entered into Kepler's Laws yield a combined mass 3.6 times that of the Sun. Psi Vel A and B have respective magnitudes of 4.1 and 4.6, the latter varying between 4.5 and 5.1 (with no known period), the brighter F3 star having a stated temperature of 7130 Kelvin, the fainter F0, but hotter, component a probable temperature of 7400 Kelvin. Respective luminosities then come in at 6 and 3.8 solar, radii at 1.6 and 1.2 solar, and masses both close to 1.5 times that of the Sun. Though classified as subgiants (stars that have given up core hydrogen fusion or are very close to it), both are clearly dwarfs, and in fact not that old. With a combined mass of 3.0 solar, there is some discrepancy with the orbital results, implying some orbital uncertainty. Spinning with a fast projected equatorial velocity of 156 kilometers per second, Psi Vel A rotates in under half a day! But now things get a bit confusing, as one source suggests that Psi Vel A is actually the warmer F0 star and the Psi Vel B the cooler F3 star, which actually makes a bit more sense from an evolutionary point of view. No matter, however, as the masses come out about the same, the small discrepancy with the orbital solution not resolved.
Written by Jim Kaler 5/02/08. Return to STARS.