mardi 23 septembre 2008

Orion 9

Iota Orionis (ι Ori / ι Orionis) is the brightest star in Orion's sword. This system is at the tip of the sword. It also has the traditional names Hatsya (sometimes with the typographic error Hatysa), or in Arabic, Na’ir al Saif, which means simply "the Bright One of the Sword."
This is a quadruple system dominated by a massive spectroscopic binary with an eccentric (e=0.764), 29-day orbit. The collision of the stellar winds from this pair makes the system a strong X-ray source.

Pi3 Orionis (π3 Ori / π3 Orionis), formally designated Tabit, is a yellow-white dwarf star approximately 26 light-years away in the constellation of Orion. It is thought that the star may, in fact, be a binary system. Though no extrasolar planets have been observed around Pi3 Orionis, the star is considered a prime location for planets as small as the Earth. Pi3 Orionis is the brightest star in the lion's hide (or shield) that Orion is holding.

Sigma Orionis or Sigma Ori (σ Orionis / σ Ori) is a five star system in the constellation Orion. It is approximately 1,150 light years from Earth.
The primary component is the binary, Sigma Orionis AB, with the two stars being a mere 0.25 arcseconds apart. Both stars are hydrogen-fusing dwarfs only a few million years old. The brighter one, Sigma Orionis A, is a blue O-type star with an apparent visual magnitude of +4.2 and is one of the most luminous stars known. Sigma Orionis B is a B-type star with an apparent visual magnitude of +5.1. The pair orbit each other every 170 years at a distance of about 90 AU. A and B have very hot surfaces, around 32,000 and 29,600 kelvins, radiating at about 35,000 and 30,000 solar luminosities, respectively. Temperature and luminosity give masses of 18 and 13.5 solar masses, making the close AB pair among the most massive of visual binaries.
The next brightest stars in the system are Sigma Orionis D and E, which lie about 4,600 and 15,000 AU respectively from the AB pair. Both are seven solar mass B-type dwarf stars with magnitudes of 6.62 and 6.66. Sigma Orionis E is a prototype of the strange "helium-rich" stars, which have significantly large amounts of helium.
The last star in the system is Sigma Orionis C, a A-type dwarf star. C is the closest to the AB pair, about 3,900 AU away. While the orbit of the AB pair is stable, the orbits of the other three are not, and long before they die they will probably be gravitationally sped up and forced out of the system.

Eta Orionis (η Ori / η Orionis) is a star in the constellation Orion. It is also known as one of Saiph, Algjebbeh, or Ensis (Latin for "sword", since the star is taken to represent Orion's sheathed weapon).
It is a star system at a distance of 900 light years from Earth and part of the Orion Arm. Eta Orionis lies a little to the west of Orion's belt between Delta Orionis and Rigel, being closer to Delta Orionis than to Rigel. It is an eclipsing binary system consisting of two blue stars orbiting one another in a regular pattern.

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