Epoch J2000 Equinox J2000
|Right ascension||08h 44m 42.22658s|
|Declination||−54° 42′ 31.7493″|
|Apparent magnitude (V)||1.96 (1.97/5.55)|
|Spectral type||A1 Va(n) + F2-F5|
|U−B color index||+0.07|
|B−V color index||+0.04|
|Variable type||Eclipsing binary|
|Radial velocity (Rv)||+2.2 km/s|
|Proper motion (μ)||RA: +28.99 mas/yr
Dec.: −103.35 mas/yr
|Parallax (π)||40.49 ± 0.39 mas|
|Distance||80.6 ± 0.8 ly
(24.7 ± 0.2 pc)
|Absolute magnitude (MV)||0.02/3.60|
|Surface gravity (log g)||3.79 cgs|
|Rotational velocity (v sin i)||150 km/s|
|Age||400 million years|
Delta Velorum (δ Vel, δ Velorum) is a star system in the southern constellation Vela, near the border with Carina. From parallax measurements, it is approximately 80.6 light-years (24.7 parsecs) from Earth. This star is sometimes given the name Koo She, Chinese for 'Bow and Arrows', along with ω Velorum and stars in Canis Major.
Delta Velorum is a triple star system. The outward components A and B have a wide orbit with a 142 year orbital period. The primary component A has an apparent magnitude of 1.97, while the secondary component B is magnitude 5.55. In 1978 the primary component was reported to be a spectroscopic binary in the Proceeding of the Australian Astronomical observatory, and this was confirmed by the Hipparcos satellite. Observations of variability in the δ Velorum system were made independently by ground-based astronomers and the Galileo spaceprobe at Jupiter.
In 2000 it was announced that the components Aa and Ab form an eclipsing binary, having an orbital period of 45.15 days and an eccentricity of 0.230. Delta Velorum is the brightest known eclipsing binary, although Algol has a deeper minimum and is easier to observe visually. Only the primary component δ Velorum A is sufficiently bright to explain such variation.
Both members of the spectroscopic binary δ Vel A are evolved stars that have left the main sequence. Component Aa has 2.5 times the mass of the Sun, 2.6 times the Sun's radius, and is radiating 56 times the luminosity of the Sun at an effective temperature of 9,470. Component Ab is only slightly smaller, with 2.4 times the Sun's mass and radius, with a luminosity of 47 times the Sun and an effective temperature of 9,370 K. The two stars are spinning rapidly and are about 400 million years old.
The Chinese name Koo She 弧矢 (Mandarin húshǐ) "Bow and Arrow", originally assigned for some[which?] stars among Canis Major, Puppis, and Vela, was introduced by Robson[who?] for this star.
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