HR 6806

HR 6806 is a solitary, orange, main sequence (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.[5] It appears to be rotating slowly with an estimated period of 42 days. The star has an inactive chromosphere, with a surface magnetic field strength of 1,500 G.[6] It is around six billion years of age.[8]

HR 6806
Observation data
Epoch 2000      Equinox 2000
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[1] mas
Distance36.189 ± 0.008 ly
(11.096 ± 0.002 pc)
Absolute magnitude (MV)6.17[4]
Details
Mass0.791+0.014
−0.008[5] M☉
Radius0.79+0.02
−0.01[5] R☉
Luminosity0.35[5] L☉
Surface gravity (log g)4.53[3] cgs
Temperature4,900[3] K
Metallicity [Fe/H]−0.61[3] dex
Rotation42 d[6]
Rotational velocity (v sin i)4.82[7] km/s
Age5.8–7.1[8] Gyr
Other designations
BD+38°3095, GJ 706, HD 166620, HIP 88972, HR 6806, SAO 66700, LHS 3363[9]
Database references
SIMBADdata

There is a nearby brown dwarf, WISE J180901.07+383805.4, at an angular separation of 769″, which would correspond to a projected separation of 8460 AU at the distance of HR 6806. However, this is most likely a typical T7 dwarf, which would place it at a 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.[10]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
  5. Marsden, S. C.; et al. (November 2014), "A BCool magnetic snapshot survey of solar-type stars", Monthly Notices of the Royal Astronomical Society, 444 (4): 3517–3536, arXiv:1311.3374, Bibcode:2014MNRAS.444.3517M, doi:10.1093/mnras/stu1663.
  6. 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.
  7. Martínez-Arnáiz, R.; et al. (September 2010), "Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter" (PDF), Astronomy and Astrophysics, 520: A79, arXiv:1002.4391, Bibcode:2010A&A...520A..79M, doi:10.1051/0004-6361/200913725.
  8. Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal, 687 (2): 1264–1293, arXiv:0807.1686, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785.
  9. "HD 166620". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-12-07.
  10. Luhman, Kevin L.; et al. (December 2012), "New M, L, and T Dwarf Companions to Nearby Stars from the Wide-field Infrared Survey Explorer", The Astrophysical Journal, 760 (2): 9, arXiv:1211.3977, Bibcode:2012ApJ...760..152L, doi:10.1088/0004-637X/760/2/152, 152.
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