HR 6806 or HD 166620 is a solitary, orange, main sequence, and Sun-like (K2 V) star located thirty-six light-years away,[10] 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.[5] 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.[6] 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,[update] the star appears to have entered the equivalent of a Maunder minimum.[10] The star is around six billion years of age.[8]
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Hercules |
Right ascension | 18h 09m 37.41628s[1] |
Declination | +38° 27′ 27.9959″[1] |
Apparent magnitude (V) | 6.40[2] |
Characteristics | |
Spectral type | K2 V[3] |
U−B color index | +0.585[2] |
B−V color index | +0.875[2] |
Astrometry | |
Radial velocity (Rv) | −19.315±0.0015[1] km/s |
Proper motion (μ) | RA: −316.520[1] mas/yr Dec.: −468.214[1] mas/yr |
Parallax (π) | 90.1264 ± 0.0200 mas[1] |
Distance | 36.189 ± 0.008 ly (11.096 ± 0.002 pc) |
Absolute magnitude (MV) | 6.17[4] |
Details | |
Mass | 0.791+0.014 −0.008[5] M☉ |
Radius | 0.79+0.02 −0.01[5] R☉ |
Luminosity | 0.35[5] L☉ |
Surface gravity (log g) | 4.53[3] cgs |
Temperature | 4,900[3] K |
Metallicity [Fe/H] | −0.61[3] dex |
Rotation | 42 d[6] |
Rotational velocity (v sin i) | 4.82[7] km/s |
Age | 5.8–7.1[8] Gyr |
Other designations | |
Database references | |
SIMBAD | data |
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.[11]