p VEL (p Velorum). That's with a lower-case "p," the fourth magnitude (3.84) star in southeastern Vela (the Sails of Argo) lying just to the northwest of Mu Vel and (farther) to the southeast of similarly-bright (3.85) "q Vel" (bright enough to be part of the constellation's outline), allowing you, as the saying goes, to "mind your p's and q's" (and as such thus just begged to be said). The lower-case Roman letters were used in Vela by Nicolas de Lacaille after he ran out of Greek letters (distributed across Argo), and we find a lot of them in such star-rich constellations. Minding them or not, the star's classification seems to be in quite a mess. It's a double, the two separated by well under a second of arc (which promotes difficulty of observation). The classes were originally given as F4 subgiant (p Vel A, the brighter) plus F3 (p Vel B, presumably a dwarf). But later sources give F0 "peculiar" for p Vel A, with the class ranging to A3 combined with hot F. We've got to pick something, so let's stay with the original and see where it takes us. The "single-star" magnitude of 3.84 comes from fourth magnitude (4.1) p Vel A (the F4 subgiant) combined with sixth magnitude (5.7) p Vel B, for which we adopt temperatures of 6800 and 6900 Kelvin (such temperatures not very critical to analysis). A good distance of 87.5 light years (give or take just 1) then gives respective luminosities of 12.6 and 2.9 times that of the Sun, the radii coming in at 2.6 and 1.2 solar. There are no modern measures of rotation, but older ones show none, the "peculiar" designation implying abundance anomalies that go along with slow spin and little atmospheric stirring, which explains the lack of consistency in overall classification. Theory then gives respective masses of 1.7 and 1.25 Suns and also shows that p Vel A is near the end of its core hydrogen-fusing life (consistent with the subgiant class) and that, with its lower mass, p Vel B is less far along its evolutionary path. The system seems to be around 1.9 billion years old. The stars are close enough to show orbital motion. An average separation of 0.37 seconds of arc translates through distance to an orbital semi-major axis of 9.86 Astronomical Units (of B as expressed around A), with a period of 16.54 years, the pair closest (in true terms, not as projected on the sky) in the latter half of 2003.
p Velorum p Velorum B orbits p Vel B (at the cross) over a period of sixteen and a half years at a mean separation of 9.9 Astronomical Units. In reality the two go about a common center of mass that lies between them. The scale is in tenths of a second of arc, the closeness of the pair making them difficult to separate. The true semimajor axis does not mark that of the apparent ellipse because of the orbital tilt to the plane of the sky and its orientation. (W. I. Hartkopf and B. D. Mason, Sixth Catalog of Orbits of Visual Binary Stars, US Naval Observatory Double Star Catalog, 2006.)
A rather high eccentricity of 0.75 takes the stars from 17.5 AU apart to as close as 2.5. Kepler's Laws then give a combined mass of 3.5 times that of the Sun, in decent agreement with a combined mass of 3.0 as derived from evolution/structure theory. Back to the top, "p" and "q" Vel have no real relation to one another. A class A (A3) dwarf, q Vel at 101 light years is somewhat farther. Only 14 light years apart, "q" would be very bright, on the high side of magnitude zero, as seen from "p," though it is highly unlikely there is anybody there to see it.
Written by Jim Kaler 4/27/12. Return to STARS.