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REGOR
(Gamma Velorum). An amazingly complex star was boded by an equally complex name. In the nineteenth century, Argo, the Ship, was divided into Vela (the Sails), Puppis (the Stern), and Carina (the Keel). Bayer originally lettered the stars within huge Argo, and when the ship was broken up, the Greek letters went with the pieces. Alpha (Canopus) and Beta are therefore in Carina, while Gamma (our star Regor) is in Vela. The Arabs referred to several of Argo's stars, which skimmed their southern horizon, as "Suhail," including Canopus. Both Regor (Gamma Velorum) and Lambda Velorum are "Suhails," Regor "Suhail al- Muhlif," or "Suhail of the Oath." While Regor is still commonly called Suhail, that name most often goes to the Vela's Lambda star, so here we will use the modern name "Regor" for Gamma. (A small telescope shows a fourth magnitude companion not quite a minute of arc away. Since the companion is east of Regor proper, it is called Gamma-1, rendering Regor Gamma-2.) Unfortunately, after all this, nobody seems to know what "Suhail" actually means! And Regor seems to be "Roger" spelled backwards. The star itself is nothing less than spectacular. Even though 840 light years away, it shines at bright second magnitude (1.78) with a hot blue white light. Called "the spectral gem of the southern skies," it is actually a pair of stars too close to be separated with the telescope. The brighter of the two is a hot evolved giant of class O, while the other is the visually brightest "Wolf-Rayet" star in the sky, the two in 78.5 day orbit about each other and separated by about the distance of Earth from Sun. From the distant companion, itself a fairly impressive hot class B star at least 10,000 astronomical units away from Regor proper, the bright duo would seem to be a brilliant double star separated by about 20 seconds of arc. Wolf-Rayet stars, named after the astronomers who discovered them, are very rare and in an extremely advanced state of age. Enormously windy, they produce powerful emissions of radiation at particular colors. They have stripped off most of their mass, their outer hydrogen envelopes, and have exposed deep helium-rich layers heavily contaminated with the by-products of nuclear fusion. They come in two flavors, nitrogen-rich and carbon-rich, Regor belonging to the latter class. Relative to helium, carbon is typically enriched by a factor of 100, and is the product of the fusion of helium. Everything about Regor excites the imagination. The more normal star of the two (if any hot class O star can be called normal) has a surface temperature of 35,000 Kelvin and radiates 200,000 times more energy (mostly in the ultraviolet) than does the Sun. With a mass of 30 times the Sun, it seems to be evolving as a giant, with a helium core. The Wolf-Rayet component is about half as luminous and contains less than 10 solar masses, but is perhaps as hot as 60,000 Kelvin. More massive stars always evolve the faster, however, so while the Wolf-Rayet component is now much less massive than the O star, it is much farther along in its evolution, hence had once to be the more massive of the two. It probably started with somewhere around 40 solar masses and has now stripped itself to a quarter of what it was. Only 4 million years old, the fainter Wolf-Rayet component is almost certainly in the last stages of preparing to blow up as a supernova.