# Kappa Velorum

Kappa Velorum (κ Velorum, abbreviated Kappa Vel, κ Vel; proper name Markeb /ˈmɑːrkɛb/) is a binary star system in the southern constellation of Vela. The two components are designated Kappa Velorum A and B.
From parallax measurements, this system is located at a distance of roughly 572 light-years (175 parsecs) from the Sun. The apparent visual magnitude is 2.48, making it readily visible to the naked eye in the southern hemisphere. It forms part of an asterism known as the False Cross along with Delta Velorum, Iota Carinae and Epsilon Carinae, so called because it is sometimes mistaken for the Southern Cross, causing errors in astronavigation.

## Nomenclature

κ Velorum (Latinised to Kappa Velorum) is the system's Bayer designation. The designations of the two components as Kappa Velorum A and B derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
The system had a traditional name Markab, from the Arabic مركب, markab meaning "something to ride". It was often spelled Markeb to distinguish it from similarly named stars such as Alpha Pegasi. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name Markeb for Kappa Velorum on 5 September 2017. Markab had previously been approved for Alpha Pegasi on 30 June 2016. Both are now included in the List of IAU-approved Star Names.
In Chinese, 天社 (Tiān Shè), meaning Celestial Earth God's Temple, refers to an asterism consisting of Kappa Velorum, Gamma$^2$ Velorum, b Velorum and Delta Velorum. Consequently, Kappa Velorum itself is known as 天社五 (Tiān Shè wǔ), "the Fifth Star of Celestial Earth God's Temple".

## Properties

Kappa Velorum is a spectroscopic binary system consisting of a pair of stars that complete an orbit around each other with a period of 116.65 days and an eccentricity of 0.19. Because the individual stars have not been resolved, further details of the orbit have not yet been determined. The combined stellar classification of the pair is B2 IV, which matches the class of a B-type subgiant star that has exhausted the hydrogen at its core and begun to evolve into a giant. The primary is about nine times more massive than the Sun, with a photospheric radius twelve times larger, irradiating 13,000 times more luminosity than the Sun at an effective temperature of 18,000 K, which give Kappa Velorum A the blue-white hue typical of B-type stars. Nothing is known about the secondary, yet.
The system is only a couple of degrees from the south celestial pole of Mars, so it could therefore be considered the southern polar star of that planet. Due to precession of the equinoxes, it will be the closest bright star of note to the south celestial pole of Earth in the period surrounding 9000 AD.

### Interstellar medium

Analysis of the spectrum of Kappa Velorum shows absorption lines due to the interstellar medium between Earth and the star. Observation of these features over many years has shown that the lines vary in strength, probably caused by a small dense cloud extending 10$^2$–10$^3$ au moving across the line of sight.