Movatterモバイル変換

[0]ホーム

p VEL (p Velorum). That's with a lower-case "p," the fourthmagnitude (3.84) star in southeasternVela(the Sails ofArgo) lying just to thenorthwest ofMu Vel and (farther) to thesoutheast of similarly-bright (3.85) "q Vel" (bright enough to bepart of theconstellation's outline),allowing you, as the saying goes, to "mind your p's and q's" (andas such thus just begged to be said). The lower-case Roman letterswere used in Vela by Nicolas de Lacaille after he ran out ofGreekletters (distributed across Argo), and we find a lot of them in such star-richconstellations. Minding them or not, the star's classificationseems to be in quite a mess. It's adouble, the two separated bywell under a second of arc (which promotes difficulty ofobservation). The classes were originally given as F4 subgiant (pVel A, the brighter) plus F3 (p Vel B, presumably a dwarf). Butlater sources give F0 "peculiar" for p Vel A, with the classranging to A3 combined with hot F. We've got to pick something, solet'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 VelB, for which we adopt temperatures of 6800 and 6900 Kelvin (suchtemperatures not very critical to analysis). A good distance of87.5 light years (give or take just 1) then gives respectiveluminosities of 12.6 and 2.9 times that of theSun, 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 goalong with slow spin and little atmospheric stirring, whichexplains the lack of consistency in overall classification. Theorythen gives respective masses of 1.7 and 1.25 Suns and also showsthat 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 seemsto be around 1.9 billion years old. The stars are close enough toshow orbital motion. An average separation of 0.37 seconds of arctranslates through distance to an orbital semi-major axis of 9.86Astronomical Units (of B as expressed around A), with a period of16.54 years, the pair closest (in true terms, not as projected onthe sky) in the latter half of 2003.

p Velorum B orbits p Vel B (at the cross) over a period of sixteenand a half years at a mean separation of 9.9 Astronomical Units. In reality the two go about a common center of mass that liesbetween them. The scale is in tenths of a second of arc, thecloseness of the pair making them difficult to separate. The truesemimajor axis does not mark that of the apparent ellipse becauseof the orbital tilt to the plane of the sky and its orientation. (W. I. Hartkopf and B. D. Mason,Sixth Catalog ofOrbits of Visual Binary Stars, US Naval Observatory Double StarCatalog, 2006.)

A rather high eccentricity of 0.75 takes the stars from 17.5 AUapart to as close as 2.5.Kepler's Laws then give a combined mass of 3.5 times that ofthe Sun, in decent agreement with a combined mass of 3.0 as derivedfrom evolution/structure theory. Back to the top, "p" and "q" Velhave no real relation to one another. A class A (A3) dwarf, q Velat 101 light years is somewhat farther. Only 14 light years apart,"q" would be very bright, on the high side of magnitude zero, asseen from "p," though it is highly unlikely there is anybody thereto see it.

Written byJim Kaler 4/27/12. Return toSTARS.

[8]ページ先頭