| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules[1] |
| Right ascension | 18h 09m 37.41621s[2] |
| Declination | +38° 27′ 27.9980″[2] |
| Apparent magnitude (V) | 6.40[3] |
| Characteristics | |
| Spectral type | K2 V[4] |
| U−B color index | +0.585[3] |
| B−V color index | +0.875[3] |
| Astrometry | |
| Radial velocity (Rv) | −19.51±0.12[2] km/s |
| Proper motion (μ) | RA: −316.454 mas/yr[2] Dec.: −468.348 mas/yr[2] |
| Parallax (π) | 90.1234±0.0156 mas[2] |
| Distance | 36.190 ± 0.006 ly (11.096 ± 0.002 pc) |
| Absolute magnitude (MV) | 6.17[5] |
| Details[6] | |
| Mass | 0.76+0.032 −0.019 M☉ |
| Radius | 0.77+0.007 −0.006 R☉ |
| Luminosity | 0.36+0.02 −0.01 L☉ |
| Surface gravity (log g) | 4.55+0.02 −0.01 cgs |
| Temperature | 4,989±48 K |
| Metallicity [Fe/H] | −0.21±0.04 dex |
| Rotation | 42.4 d |
| Rotational velocity (v sin i) | <2.0 km/s |
| Age | 10.09+2.73 −3.76 Gyr |
| Other designations | |
| BD+38°3095, GJ 706, HD 166620, HIP 88972, HR 6806, SAO 66700, LHS 3363[7] | |
| Database references | |
| SIMBAD | data |
HD 166620 or HR 6806 is a solitary, orange, main sequence, and Sun-like (K2 V) star located thirty-six light-years away,[8] 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.[9] 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.[10] From 1990 activity in the chromosphere increased, in line 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.[8] The star is around six billion years of age.[11]
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 HD 166620. 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.[12]
This star has been targeted by planet searches using the radial velocity method, but as of 2023 no evidence of a planetary companion has been found. Observations rule out the existence of planets down to super-Earth masses with orbital periods less than 2,800 days; at periods less than 10 days, planets less massive than Earth would be detectable.[6]
References
[edit]- ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
- ^ a b c d e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
- ^ 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, S2CID 119476992.
- ^ 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, S2CID 118577511.
- ^ a b John, A. Anna; Collier Cameron, A.; et al. (October 2023). "Sub-m s-1 upper limits from a deep HARPS-N radial-velocity search for planets orbiting HD 166620 and HD 144579". Monthly Notices of the Royal Astronomical Society. 525 (2): 1687–1704. arXiv:2308.01348. Bibcode:2023MNRAS.525.1687J. doi:10.1093/mnras/stad2381.
- ^ "HD 166620". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-12-07.
- ^ a b 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. 163 (4). American Astronomical Society: 183. arXiv:2203.13376. Bibcode:2022AJ....163..183B. doi:10.3847/1538-3881/ac5683. ISSN 0004-6256.
- ^ 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.
- ^ 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.
- ^ 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, S2CID 27151456.
- ^ 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, S2CID 51010785, 152.
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