Spectacular Gamma Velorum

13 Feb 2019

Shining at magnitude 1.78 with a hot blue-white light, Gamma Velorum is nothing less than spectacular. Located about 840 light years away, it is a complex multi star complex, and the brightest component, Gamma2 Velorum (or Gamma Velorum A), is a spectroscopic binary consisting of the closest known Wolf-Rayet star to Earth and a massive blue giant or blue supergiant (spectral type O7.5Ie) orbiting around each other with a period of 78.5 days at a mean separation of 1 AU. Both O-type stars and Wolf-Rayet stars are rare, the latter in particular – and here we have a naked eye example. (I confess that I wish the Wolf-Rayet star, which is well on its way to blowing itself to smithereens in a supernova, would do so – what a magnificent occurence that would be for us stargazers!)

It is called “the spectral gem of the southern skies,” for good reason. Irish astronomer Agnes Clerke (1842-1907) wrote: “An intensely bright line in the blue, and the gorgeous group of three bright lines in the yellow and orange, render the spectrum …incomparably the most brilliant and striking in the whole heavens.” She added that “a vivid continuous spectrum extends into the violet as far as the eye has power to follow it, and accounts for the brilliant whiteness of the star.” (see Burnham’s Celestial Handbook Vol. 3, page 2035).

*Gamma Velorum’s gorgeous spectrum. Image credit Mike Springer*

I have an eyepiece spectroscope and often turn my telescope to the star in order to gaze at those “gorgeous” emission lines; no image can do them justice and I will never tire of them.

*Gamma Velorum is a brilliant and beautiful sight in the telescope.*

They are a delight in the eyepiece:

Mag 4.3 Gamma1 Velorum (Gamma Velorum B) lies closest to Gamma Velorum2. The blue-white subgiant B star lies 41.2 arcsec from the Wolf-Rayet binary, (a separation that is easily resolvable in my 10×50 binoculars).

Mag 8.5 Gamma Velorum C is a white A-type star separated by 62.3 arcsec from Gamma2.

The mag 9.4 binary pair Gamma Velorum D lies 93.5 arcsec away from Gamma2. The primary is another A-type star and its companion is a mag 12.5 star, separated by 1.8 arcsec.

Interestingly, Gamma Velorum is the brightest star in Vela. During his famous 1751-1753 expedition to South Africa to chart the southern skies Nicolas de Lacaille dismantled the enormous and ancient constellation Argo. The ship was divided into Vela (the Sails), Puppis (the Stern), and Carina (the Keel). He then applied Greek letters to Argo as if it were one constellation, so with the breakup of the Ship, they went with the pieces. Alpha (Canopus) and Beta (Miaplacidus) are therefore in Carina, while Gamma is in Vela.