Astronomy:HR 6806
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| 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 |
| 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 |
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]
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]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data (SIMBAD), Bibcode: 1986EgUBV........0M.
- ↑ 3.0 3.1 3.2 3.3 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, doi:10.1086/504637, Bibcode: 2006AJ....132..161G.
- ↑ 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, doi:10.1051/0004-6361/200811191, Bibcode: 2009A&A...501..941H.
- ↑ 5.0 5.1 5.2 5.3 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, doi:10.1093/mnras/stu1663, Bibcode: 2014MNRAS.444.3517M.
- ↑ 6.0 6.1 Basri, Gibor; Marcy, Geoffrey W. (July 1988), "Physical realism in the analysis of stellar magnetic fields", Astrophysical Journal, Part 1 330: 274–285, doi:10.1086/166471, Bibcode: 1988ApJ...330..274B.
- ↑ 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", Astronomy and Astrophysics 520: A79, doi:10.1051/0004-6361/200913725, Bibcode: 2010A&A...520A..79M, http://eprints.ucm.es/37826/1/davidmontes17libre.pdf, retrieved 2018-11-04.
- ↑ 8.0 8.1 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, doi:10.1086/591785, Bibcode: 2008ApJ...687.1264M.
- ↑ "HD 166620". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+166620.
- ↑ 10.0 10.1 Baum, Anna C.; Wright, Jason T. et al. (March 22, 2022). "Five Decades of Chromospheric Activity in 59 Sun-like Stars and New Maunder Minimum Candidate HD 166620". The Astronomical Journal (American Astronomical Society) 163 (4): 183. doi:10.3847/1538-3881/ac5683. ISSN 0004-6256. Bibcode: 2022AJ....163..183B.
- ↑ 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, doi:10.1088/0004-637X/760/2/152, 152, Bibcode: 2012ApJ...760..152L.
External links
- "ARICNS: 01473". ARICNS. Centre of Astronomy, Heidelberg University. https://wwwadd.zah.uni-heidelberg.de/datenbanken/aricns/cnspages/4c4c01473.htm.
- NStars: 1809+3827[yes|permanent dead link|dead link}}]
 |  |
