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Zeta Reticuli

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Author Topic: Zeta Reticuli  (Read 2082 times)
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« on: July 31, 2011, 03:48:03 am »

This system consists of a pair of stars that are both similar in physical characteristics to the Sun. Their stellar classification is nearly identical to the Sun,[7] and they are considered solar analogs. 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.[3][4]

The two stars are somewhat deficient in metals, having only 60% of the proportion of elements other than hydrogen and helium compared to the Sun.[2][8] For reasons that remain uncertain, they have an anomalously low abundance of beryllium.[5] 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.[9]

ζ1 has an intermediate level of magnetic activity in its chromosphere.[10] 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.[11]

On September 20, 1996, a tentative discovery of a hot Jupiter around ζ2 was reported, but the discovery was quickly retracted as the signal was shown to be caused by pulsations of the star.[12] In 2002, ζ1 was examined at an infrared wavelength of 25 μm, but no indication of an excess of infrared radiation was found.[13] In 2007, the Spitzer Space Telescope was used to find an infrared excess at a wavelength of 70 μm around ζ2. This radiation is likely being emitted by a debris disk with a mean temperature of 150 K (−123 °C) that is orbiting the host star at a distance of 4.3 AU.[14] In 2010, the Herschel Space Observatory, looking for debris disks analogous to the Kuiper belt, around sun like stars, detected signs of a possible exo-kuiper belt, with a semi-major axis of 100 AU around ζ2.[15]

Both stars share similar proper motions, radial velocities and distances,[7] confirming that they form a wide binary star system. The stars have an angular separation of 309.2 arc seconds (5.2 arc minutes);[9] far enough apart to appear as a close pair of separate stars to the naked eye with a dark sky. The distance between the two stars is about 3750 AU.[16]

This star system belongs to the Zeta Herculis Moving Group of stars with common motions through space. The space velocity components of this system are (U, V, W) = (−70.2/−69.7, −47.4/−46.4, +16.4/+16.Cool km/s.[2] They are currently on an orbit through the Milky Way galaxy that has an eccentricity of 0.24. This orbit will carry the system as close as 17.4 kly (5.33 kpc) and as far as 28.6 kly (8.77 kpc) from the galactic core. The inclination of this orbit will carry the stars as much as 1.3 kly (0.4 kpc) from the plane of the galactic disk.[17] This likely puts them outside the thick disk population of stars.[18]
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