At magnitude 1.78, Gamma Velorum is the brightest star in the constellation Vela, and one of the brightest stars in the southern night sky. Vela represents the sails of the great ship Argo Navis, sailed by Jason on his quest for the Golden Fleece.
Gamma Velorum has the traditional name Suhail al-Muhlif (alternately Al Suhail, Alsuhail, Suhail al Muhlif, Muliphein), which is is short for the Arabic phrase "suhayl al-muhlif", meaning "The glorious (star) of the oath". Confusingly, the name Suhail is also applied to λ Vel.
Gamma Velorum also has the more modern popular name Regor, which is "Roger" spelled backwards, and honors the Apollo astronaut Roger Chaffee. It was originally inserted onto NASA navigational star charts by fellow astronaut Gus Grissom as a practical joke, but has since endured as a memorial to both astronauts, who died in the 1967 Apollo 1 fire.
Components
Gamma Velorum is a spectacular and complex multiple star system. The brightest component, γ2 Vel (or γ Vel A), is actually a spectroscopic binary, dubbed "the spectral gem of the southern skies." With a period of 78.5 days, the components of this binary have an average separation of 1.2 AU, but a fairly eccentric orbit that takes them as close as 0.8 AU.
The second-brightest component, at magnitude 4.27, is γ1 Vel (or γ Vel B). It lies 41.2" from the binary γ2 Vel - a separation easily resolvable with binoculars. The system also has several fainter companions. γ Vel C, a white class A star of magnitude +8.5, is separated by 62.3" from γ2 Vel. The binary pair γ Vel D and E lies 93.5" away; the D component is another class A star of magnitude +9.4; its companion is a 13th magnitude star separated by 1.8".
Properties and Evolution
The brighter of the γ2 Vel binary is a hot, massive, class O7.5 Ie supergiant. Based on comparisons with similar stars, it has a luminosity around 180,000 suns, a temperature of 32500 K, a radius 13 times solar, and a mass around 30 suns. Its binary companion is the visually brightest "Wolf-Rayet" star in the sky, of spectral class WC8. It is much hotter (57,000 to 70,000 K), with a luminosity of 100,000 suns, most of it in the ultraviolet part of the spectrum.
Wolf-Rayet stars, named after the astronomers who discovered them, are very rare and in an extremely advanced state of evolution. They produce powerful stellar winds that have stripped off most of their outer hydrogen envelopes, and have exposed deep helium-rich layers heavily contaminated with the by-products of nuclear fusion. γ Vel B is carbon-rich, with carbon (the product of helium fusion) enriched relative to helium by a factor of 100.
More massive stars evolve faster, so while the Wolf-Rayet component is now less massive than the O star, it is much farther along in its evolution, and hence was once the more massive of the two. The WR star probably started out with around 40 solar masses, but has shed much of that original material, and is left with only about 10 solar masses today. Both stars generate powerful mass-losing stellar winds, the WR star at a rate more than 100 million times that of the solar wind; the mass-loss rate of the O star is some 25 times less. The collision between the stellar winds produces X-ray emissions. Only a few million years old, the Wolf-Rayet star is almost certainly in its last stages of its life, preparing to go supernova. The O star will follow the same path.
γ2 Vel may be a member of the Vela OB2 association of hot class O and B stars. Its distant companion, γ1 Vel, is itself a fairly impressive hot class B star at least 15,000 AU away. Unfortunately, the system's distance is not well known. Parallax gives 840 light years, but measures of the angular separation between the stars, coupled with the known orbit, give a distance of 1200 light years.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]