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Zeta Reticuli (Zeta Ret, ζ Reticuli, ζ Ret) is a wide binary star system in the southern constellation of Reticulum. From the southern hemisphere the pair can be seen as a naked eye double star in very dark skies. Based upon parallax measurements, this system is located at a distance of about from the Earth. Zeta2 Reticuli is orbited by a circumstellar debris disk. Both stars are solar analogs that share similar characteristics with the Sun. They belong to the Zeta Herculis Moving Group of stars that share a common origin. == Characteristics == The double star Zeta Reticuli is located in the western part of the small Reticulum constellation, about 25′ from the constellation's border with Horologium. In dark southern skies, the two stars can be viewed separately with the naked eye, or with a pair of binoculars.〔 ζ1 Reticuli has an apparent magnitude of 5.52,〔 placing it on the border between 5th and 6th magnitude stars. ζ1 Reticuli is slightly brighter at magnitude 5.22.〔 At a declination of −62°, the system is not visible from Britain's latitude of +53°, so it never received a Flamsteed designation in John Flamsteed's 1712 ''Historia Coelestis Britannica''. The Bayer designation for this star system, Zeta (ζ) Reticuli, originated in a 1756 star map by the French astronomer Abbé Nicolas Louis de Lacaille.〔 Subsequently, the two stars received separate designations in the Cape Photographic Durchmusterung, which was processed between 1859 and 1903, then in the Henry Draper Catalogue, published between 1918 and 1924.〔 The two stars are located at similar distances from the Sun and share the same motion through space,〔 confirming that they are gravitationally bound and form a wide binary star system. They have an angular separation of 309.2 arc seconds (5.2 arc minutes);〔 far enough apart to appear as a close pair of separate stars to the naked eye under suitable viewing conditions. The distance between the two stars is at least 3,750 AU, so their orbital period is 170,000 years or more.〔 Both stars share similar physical characteristics to the Sun,〔 so they are considered solar analogs. Their stellar classification is nearly identical to that of the Sun. ζ1 has 96% of the Sun's mass and 84% of the Sun's radius. ζ2 is slightly larger and more luminous than ζ1, with 99% of the Sun's mass and 88% of the Sun's radius.〔〔 The two stars are somewhat deficient in metals, having only 60% of the proportion of elements other than hydrogen and helium as compared to the Sun.〔〔 For reasons that remain uncertain, ζ1 has an anomalously low abundance of beryllium.〔 Two possible explanations are: during the star's formation it underwent multiple intense bursts of mass accretion from a rapidly rotating protostellar cloud, or else the star underwent rotational mixing brought on by a period of rapid rotation during the star's youth.〔 Both stars are considered unusual because they have a lower luminosity than is normal for main sequence stars of their age and surface temperature. That is, they lie below the main sequence curve on the Hertzsprung-Russell diagram for newly formed stars. Most stars will evolve above this curve as they age.〔 ζ1 has an intermediate level of magnetic activity in its chromosphere.〔 Although the kinematics of this system suggest that they belong to a population of older stars, the properties of their stellar chromospheres suggests that they are only about 2 billion years old.〔 This star system belongs to the Zeta Herculis Moving Group of stars that share a common motion through space, suggesting that they have a common origin. In the galactic coordinate system, the components of the space velocity for this system are equal to for ζ1 and for ζ2.〔 They are currently following an orbit through the Milky Way galaxy that has an eccentricity of 0.24. This orbit will carry the system as close as and as far as from the Galactic Center. The inclination of this orbit will carry the stars as much as from the plane of the galactic disk.〔 This likely puts them outside the thick disk population of stars.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Zeta Reticuli」の詳細全文を読む スポンサード リンク
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