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(Redirected from HD 166620)
Star in the constellation Hercules
HR 6806 or HD 166620 is a solitary, orange, main sequence, and Sun-like (K2 V) star located thirty-six light-years away, in the constellation Hercules. The star is smaller than the Sun, with around 79% of the solar mass and radius, and 35% of the solar luminosity. It appears to be rotating slowly with an estimated period of 42 days. In 1988, it was noticed that the star had an inactive chromosphere, with a surface magnetic field strength of only 1,500 G. From 1990 activity in the chromosphere increased, inline with a 16 year stellar cycle previously observed. But, sometime after 1994 (exact date unknown because of a data collection gap between 1995 and 2004) chromospheric activity greatly reduced, and has stayed flat for more than 16 years. As of 2022, the star appears to have entered the equivalent of a Maunder minimum. The star is around six billion years of age.
There was suspected to be a nearby very cool, and very dim, T9 to Y brown dwarf companion, WISE J180901.07+383805.4, at an angular separation of 769″, which would have corresponded to a projected separation of 8460 AU at the distance of HR 6806. However, with further observation it was found to be bluer than at first thought and more typical of a slightly brighter T7 dwarf, which would place it at a much greater distance of 91 ly (28 pc)—ruling out a physical association. This is confirmed by the differing proper motion of the star and this object.
^ Basri, Gibor; Marcy, Geoffrey W. (July 1988), "Physical realism in the analysis of stellar magnetic fields", Astrophysical Journal, Part 1, 330: 274–285, Bibcode:1988ApJ...330..274B, doi:10.1086/166471.
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