MARKEB (Kappa Velorum). Markeb, of Vela, comes (according to Kunitzsch and Smart) from "markab," which refers to a vehicle of some sort (here Argo, the Ship, of which Vela represents the sails). It is not to be confused with the star name "Markab" (Alpha Pegasi), which is a corruption of "mankib" and refers to the shoulder of the flying horse. It's no wonder that astronomers long ago began using more logical Greek letters, numbers, and other stellar designations from extensive catalogues. Markeb has several claims to prominence. First, adopting values from the Yale Bright Star Catalogue, it is the faintest of the second magnitude stars, coming in right at magnitude 2.50 (91st in brightness, though some other sources place it as bright as 2.46). Second, Markeb is the faintest member of the prominent four-star "False Cross." Lying near a rich part of the Milky Way, the figure rather nicely resembles Crux, the famed Southern Cross, and also includes Avior (Epsilon Carinae), Aspidiske (Iota Car), and Kappa's brighter constellation-mate, Delta Velorum. Third, while not very extensively observed, Kappa Vel has some impressive properties. Shining from a distance of 540 light years, its light dimmed by 0.2 magnitudes by interstellar dust, this hot (estimated at 22,300 Kelvin) blue class B (B2) subgiant-dwarf radiates at rate of 18,400 Suns (most in the ultraviolet), from which we find a radius of 9.1 times solar. Temperature and luminosity combine to imply a mass of between 10 and 11 times that of the Sun, and reveal a star that --consistent with its subgiant status -- is near the end of its 16-20 million-year hydrogen-fusing life. An equatorial rotation speed of at least 52 kilometers per second gives a rotation period less than 8.7 days. Next, as learned from its spectrum, Markeb has a companion that orbits in just 116.65 days at an average separation of at least half an Astronomical Unit. Assuming that the companion contains a solar mass, the true separation is closer to 1.1 AU, implying an orbital tilt to the plane of the sky of 26 degrees, which in turn suggests (if the axial tilt is the same as the orbital) a true rotation period of just 4 days. Markeb, which is rather windy and is losing mass at a rate of roughly a billionth of a solar mass per year, also radiates X-rays, which may be coming either from the star itself, or from magnetic activity in the lesser companion. No one really knows. The fate of the star is not well determined either, as it is near the dividing line at which stars become either massive white dwarfs or blow up as supernovae. With its simple spectrum, Markeb is particularly important as a background source of light with which to study the intervening gases of interstellar space.
Written by Jim Kaler. Return to STARS.