Regor: The Spectral Gem of the Southern Skies
The closest stars to Earth within different categories appear to be very easily accessible, their distances suspended within the double digits. Conversely, a rare and special type of star closes out the crowd, with its nearest representative to us standing over 1,000 light years away: Wolf-Rayet stars, coruscating conduits which shine like violets in the sky, are an incredibly rare type of light with an unusual spectrum. Nevertheless, the category’s closest member to us shines as the warm and welcoming 30th brightest star in our entire aether: Regor, Gamma Velorum, is commonly nicknamed by astronomers “The Spectral Gem of the Southern Skies.”
Before I elaborate on Regor’s grandeur, a foundational understanding of Wolf-Rayet stars is required in order to understand what I am discussing. Wolf-Rayet stars are a scarce type of O-type stars (the hottest class) primarily special for their spectra: their emission lines (lines on a spectrum showing astronomers what elements stars are abundant in) display high quantities of ionized helium, nitrogen, carbon, and in profoundly rare cases, oxygen. Additionally, Wolf-Rayet stars must have twenty or more solar masses in order to qualify, and an incredibly strong solar wind (the flow of mass leaving a star and being ejected throughout space). Despite this, the strangest quality possessed by Wolf-Rayet stars is that many of them display absolutely no hydrogen in their spectra whatsoever, and consequently, many of them are composed more of heavy elements than helium. Moreover, Wolf-Rayet stars are so strange, in fact, that they have a spectral class system of their own.
Regular stars receive spectral types based on their temperature and evolutionary stage. The letter in their spectral type (O, B, A, F, G, K, or M) represents their temperature, along with a number from 0–9 (lower is warmer) narrowing down the star’s range. They are then followed by a letter representing their evolutionary stage (V means main sequence, IV means subgiant, II/III means giant and Iab/Ia means supergiant). So, for example, Vega’s spectral type A0V indicates it is a blue-white main sequence star. Aldebaran’s K5III means it is an orange-red giant. Clearly, Wolf-Rayet stars like Regor cannot be placed within these boundaries, and require a system of their own in order to be fully understood.
The spectral type of all Wolf-Rayet stars begins with the letter “W”, followed by another letter based on the star’s chemical composition. Wolf-Rayet stars are split into three different categories: WN (Stars with a strong abundance of ionized nitrogen), WC (Stars with a strong abundance of ionized carbon), and WO (Stars with a strong abundance of ionized oxygen). For reference, Regor is a WC star with exceptional prosperity of carbon. Posterior to this, they’re assigned numbers not based on their temperature, but on the emission lines they have in their spectra. Accordingly, the assignment of these numbers is incredibly complex and would require its own explainer (thankfully, it is not important to this article). Furthermore, with Wolf-Rayet stars explained, it’s time to talk about Regor, the Spectral Gem of the Southern Skies.
Regor, of spectral class WC8 (Bayer designation Gamma2 Velorum), is a Wolf-Rayet star with 170,000 times the luminosity of our sun, and a temperature of 57,000 Degrees Kelvin. If Regor weren’t a Wolf-Rayet star, it would be of spectral class O2, the absolute hottest type of star. However, what makes Regor so interesting isn’t what it does on its own, but its kinematics with its O-type binary companion. Regor’s O-type star, of spectral type O7.5III (A temperature of 35,000 Kelvin), is conversely far more luminous than the Wolf-Rayet star. It has a luminosity of 280,000 suns, implying it shines 1.6 times brighter than the other component. The two stars are incredibly close, around 1.0 Astronomical Units from each other, or the approximate distance between Earth and The Sun. The stars take 78 days to orbit each other around a center of gravity; ten days shorter than Mercury’s time to orbit around the sun.
Regor’s two components will likely perish in a type Ib supernova, making it one of the nearest supernova candidates to Earth. A type Ib supernova occurs once the core of a massive star collapses in on itself, causing the star to spew its matter across space in order to form a type of nebula known as a supernova remnant. Depending on the star’s final mass, it will either leave a neutron star (in special cases, a Pulsar/Magnetar) or a black hole behind. Regor’s supernova isn’t suspected to happen very soon, however, it could be on the radar since it has already shed its hydrogen layer. The loss of a star’s hydrogen layer is a key factor in guessing when a type Ib supernova will happen, however, this feature is normal in Wolf-Rayet stars and can’t ring much of a bell.
However, just two stars weren’t enough for Regor. The star I’ve been talking about throughout this article is named Gamma2 Velorum and is orbited by the separate binary system Gamma1 Velorum, ultimately making Regor a quadruple star. Despite Gamma1 Velorum being a system of two stars, only one’s spectral class has been properly identified: B1IV/III (Some assume that its companion is identical to it, but we don’t know for sure). The two components of Gamma1 Velorum have an extremely tight orbit, taking just 1.5 days to orbit each other once. Whilst Gamma1 Velorum can easily be separated by Gamma2 Velorum with the use of optical aid, the two components of Gamma1 Velorum may only be observed separately using very special technology.
Despite being a quadruple star, Regor is associated with various other systems due to its affiliation with the Vela OB2 Association. The Vela OB2 association is a group of stars that have a common proper motion through space together. It’s called the “OB” association since it’s mainly composed of stars with spectral types O and B (The two hottest on the spectrum). It’s additionally composed of very young stars, but none of them are incredibly famous or luminous like Regor, so Vela OB2 has consequently been nicknamed the “Gamma Velorum Cluster.”
Interestingly enough, since Vela OB2 is mainly composed of young stars, it has been discovered that Regor is also associated with hundreds of pre-main sequence stars, or protostars. Whilst Regor does not actually interact with any of the young stars, it is fascinating for astronomers to see that so many of them share a proper motion through space with it.
So, when you’re admiring the shimmering sails of Vela, fix your gaze to peer upon the Spectral Gem of the Southern Skies and all of the glory which it possesses. With the vast majority of the Milky Way’s Wolf-Rayet stars in a whirlwind around the Galactic Center, Regor’s whereabouts so near and dear to us truly close out the crowd.
