Gamma Velorum

Gamma Velorum (γ Vel, γ Velorum) is a multiple star system in the constellation Vela. At magnitude +1.7, it is one of the brightest stars in the night sky, and by far the closest and brightest Wolf-Rayet star. It has the traditional name Suhail al Muhlif and the modern name Regor, but neither is approved by the International Astronomical Union.

Gamma Velorum is close enough to have accurate parallax measurements as well as distance estimates by more indirect means. The Hipparcos parallax for γ² implies a distance of 342 pc. A dynamical parallax derived from calculations of the orbital parameters gives a value of 336 pc, similar to spectrophotometric derivations. A VLTI interferometry measurement of the distance gives a slightly larger value of 368+38
−13 pc. All these distances are somewhat less than the commonly assumed distance of 450 pc for the Vela OB2 association which is the closest grouping of young massive stars.

The Gamma Velorum system is composed of at least four stars. The brightest member, γ² Velorum or γ Velorum A, is a spectroscopic binary composed of a blue supergiant of spectral class O7.5 (~30 M_☉), and a massive Wolf-Rayet star (~9 M_☉, originally ~35 M_☉). The binary has an orbital period of 78.5 days and separation varying from 0.8 to 1.6 astronomical units. The Wolf-Rayet star is likely to end its life in a Type Ib supernova explosion; it is one of the nearest supernova candidates to the Sun. The Wolf Rayet star has traditionally been regarded as the primary since its emission lines dominate the spectrum, but the O star is visually brighter and also more luminous. For clarity, the components are now often referred to as WR and O.