Vela (constellation)

Vela is a constellation in the southern sky, which contains the Vela Supercluster. Its name is Latin for the sails of a ship, and it was originally part of a larger constellation, the ship Argo Navis, which was later divided into three parts, the others being Carina and Puppis. With an apparent magnitude of 1.8, its brightest star is the hot blue multiple star Gamma Velorum, one component of which is the brightest Wolf-Rayet star in the sky. Delta and Kappa Velorum, together with Epsilon and Iota Carinae, form the asterism known as the False Cross. 1.95-magnitude Delta is actually a triple or quintuple star system.

 History 
Argo Navis was one of the 48 classical constellations listed by the 2nd-century astronomer Ptolemy, and represented the ship Argo, used by Jason and the Argonauts on their quest for the Golden Fleece in Greek mythology. German cartographer Johann Bayer depicted the constellation on his Uranometria of 1603, and gave the stars Bayer designations from Alpha to Omega. However, his chart was inaccurate as the constellation was not fully visible from the Northern Hemisphere.

Argo was more accurately charted and subdivided in 1752 by the French astronomer Nicolas Louis de Lacaille, forming Carina (the keel), Vela (the sails), and Puppis (the poop deck). Despite the division, Lacaille kept Argo's Bayer designations. Therefore, Carina has the Alpha, Beta and Epsilon originally assigned to Argo Navis, while Vela's brightest stars are Gamma and Delta, Puppis has Zeta as its brightest star, and so on.

 Characteristics 
Vela is bordered by Antlia and Pyxis to the north, Puppis to the northwest, Carina to the south and southwest, and Centaurus to the east. Covering 500 square degrees, it ranks 32nd of the 88 modern constellations in size. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Vel".

The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 14 segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 08h 13.3m and 11h 05.5m , while the declination coordinates are between −37.16° and −57.17°.

 Features 

 Stars[edit] 
See also: List of stars in Vela

The brightest star in the constellation, Gamma Velorum, is a complex multiple star system. The brighter component, known as Gamma2 Velorum, shines as a blue-white star of apparent magnitude 1.83. It is a spectroscopic binary made up of two very hot blue stars orbiting each other every 78.5 days and separated by somewhere between 0.8 and 1.6 Astronomical Units (AU). The brighter component is a hot blue main-sequence star of spectral type O7.5 and is around 280,000 times as luminous, is around 30 times as massive and is 17 times the diameter of the Sun with a surface temperature of 35,000 K. The second component is an extremely rare example of hot star known as a Wolf–Rayet star, and is the brightest example in the sky. It has a surface temperature of 57,000 and is around 170,000 times as luminous as the Sun, though it radiates most of its energy in the ultraviolet spectrum. Gamma1 is a blue-white star of spectral type B2III and apparent magnitude 4.3. The two pairs are separated by 41 arcseconds, easily separable in binoculars. Parallax measurements give a distance of 1,116 light-years, meaning that they are at least 12,000 AU apart. Further afield are 7.3-magnitude Gamma Velorum C and 9.4-magnitude Gamma Velorum D, lying 62 and 93 arcseconds south-southeast from Gamma2.

The next brightest star is Delta Velorum or Alsephina, also a multiple star system and one of the brightest eclipsing binaries in the sky. Together with Kappa Velorum or Markeb, Iota Carinae or Aspidiske and Epsilon Carinae or Avior, it forms the diamond-shaped asterism known as the False Cross—so called because it is sometimes mistaken for the Southern Cross, causing errors in astronavigation. Appearing as a white star of magnitude 1.95, Delta is actually a triple or possibly quintuple star system located around 80 light-years from the Solar System. Delta A has a magnitude of 1.99 and is an eclipsing binary composed of two A-type white stars (Delta Aa and Ab) which orbit each other every 45.2 days and lie 0.5 AU from each other, with a resulting drop in magnitude of 0.4 when the dimmer one passes.in front of the brighter. Delta B is a 5.1 magnitude yellow G-class star of similar dimensions to the Sun which ranges between 26 and 72 AU away from the brighter pair, taking 142 years to complete a revolution. Further out still, at a distance of 1700 AU, are two red dwarfs of magnitudes 11 and 13. If they are part of the multiple system, they take 28000 years to complete an orbit. Also called Markeb, Kappa appears as a blue-white star of spectral type B2IV-V and magnitude 2.47 but is in fact a spectroscopic binary. The two orbit around each other with a period of 116.65 days, but the size, mass and nature of the companion are as yet unclear.

The orange-hued Lambda Velorum, or Suhail, is the third-brightest star in the constellation. A supergiant of spectral type K4Ib-II, it varies between magnitudes 2.14 and 2.3, and lies 545 light-years distant. It has around 11,000 times the luminosity, 9 to 12 times the mass and 207 times the diameter of the Sun.

AH Velorum is a Cepheid variable located less than a degree to the northeast of Gamma. A yellow-white supergiant of spectral type F7Ib-II, it pulsates between magnitudes 5.5 and 5.89 over 4.2 days. Also lying close to Gamma, V Velorum is a Cepheid of spectral type F6-F9II ranging from magnitude 7.2 to 7.9 over 4.4 days. AI Velorum is located 2.8 degrees north-northeast of Gamma, a Delta Scuti variable of spectral type A2p-F2pIV/V that ranges between magnitudes 6.15 and 6.76 in around 2.7 hours.

V390 Velorum is an aged star that has been found to be surrounded by a dusty disk. An RV Tauri variable, it has a spectral type of F3e and ranges between magnitudes 9.01 and 9.27 over nearly 95 days.

Omicron Velorum is a blue-white subgiant of spectral type B3III-IV located around 495 light-years from the Solar System. A slowly pulsating B star, it ranges between magnitudes 3.57 and 3.63 over 2.8 days. It is the brightest star in, and gives its name to, the Omicron Velorum Cluster, also known as IC 2391, an open cluster located around 500 light-years away.

Seven star systems have been found to have planets. HD 75289 is a Sun-like star of spectral type G0V with a hot Jupiter planetary companion that takes only about 3.51 days to revolve at an orbital distance of 0.0482 AU. WASP-19 is a star of apparent magnitude 12.3 located 815 light-years away, which has a hot Jupiter-like planet that orbits every 0.7 days. HD 73526 is a Sun-like star of spectral type G6V that has two planets around double the mass of Jupiter each with orbits of 187 and 377 days, respectively.

HD 85390 is an orange dwarf of spectral type K1.5V lying around 111 light-years distant with a planet 42 times as massive as Earth orbiting every 788 days.

HD 93385 is a Sun-like star of spectral type G2/G3V located around 138 light-years away that is orbited by two super-Earths with periods of 13 and 46 days and masses 8.3 and 10.1 times that of Earth, respectively.

Category:Constellations