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The multiple stellar system Velδ (HD 74956, HIP 41913, GJ 321.3, GJ 9278) contains one of the nearest and brightest eclipsing binaries. The binarity of Vel was discovered by S. I. Baδiley in 1894 from Arequipa, Peru (and independently by Innes 1895). It has already been known as a quadruple system for many years as IDS 08419-5420 (Jeffers et al., 1963) The system contains two pairs which are located apart at an angular separation of 69 arcsec. The bright close pair AB is separated by 2". The distant satellite binary system CD has its components of 11m and 13m splitted by 6".

In 1978 the primary component A was reported to be a spectroscopic binary (sep. 0”.6) in the Proceeding of the Australian Astronomical observatory (Tango et al., 1979), making the whole system quintuple. This was later confirmed by the Hipparcos satellite (0".736, Perryman et al., 1997). Being composed of two A-type in rapid rotation and one F-type main sequence stars, Vel δAB is particularly interesting to astrophysicists, because of its close distance to the Sun.

With a revised Hipparcos parallax of 40.49 ± 0.39mas (van Leeuwen, 2007), it is just 80.6 light-years away. The outward components A and B have a wide orbit with a 142 year orbital period at an average distance of 49 AU. The primary component A has an apparent magnitude of 1.97, while the secondary component B is magnitude 5.55. Delta Vel C and D, two probable class M red dwarfs of magnitudes 11 and 13.5 at least 150 AU apart and orbit over a period of at least two thousand years.

In 2000 it was announced that the components Aa and Ab form an eclipsing binary (Otero et al., 2000), having an orbital period of 45.150 days (a ~ 0.5 AU) and an eccentricity of 0.230 (Ammler-von Eiff, M., 2011). The system probably contains two early A-type stars (Otero et al., 2000). Surprisingly enough, Delta Velorum became one of the brightest known eclipsing binaries in the sky, one of the very few observable with the unaided eye. Although Algol has a deeper minimum and is much easier to observe visually.

Orbital period of 45 days seems to be remarkably long for most known eclipsing binaries. The Vel δsystem is also notice-able for another reason. Because of precession (the 26,000-year wobble of the Earth's axis), Vel will be a South Pole star aroundδ 9000 AD. Being close to out Solar system, Delta Velorum there-fore presents an unique opportunity to determine independently the physical properties of the three components of the system. The components Aa and Ab are bright fast rotating stars, with masses of 2.53M and 2.37 ⊙M⊙( 4% accuracy) ≈respectively, and the mass of Vel B δis estimated to be 1.5 ≈M.

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