Rho Capricorni

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Rho Capricorni
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Capricornus
Right ascension 20h 28m 51.61448s[1]
Declination −17° 48′ 49.2693″[1]
Apparent magnitude (V) +4.78[2] (4.97 + 6.88)[3]
Spectral type F2 IV[2] + G1[4]
Radial velocity (Rv) +18.4[5] km/s
Proper motion (μ) RA: −14.98[1] mas/yr
Dec.: −7.29[1] mas/yr
Parallax (π) 33.04 ± 0.46[1] mas
Distance 99 ± 1 ly
(30.3 ± 0.4 pc)
Absolute magnitude (MV) 2.52 + 4.56[4]
Period (P) 278 yr
Semi-major axis (a) 1.877″
Eccentricity (e) 0.91
Inclination (i) 113.3°
Longitude of the node (Ω) 162.0°
Periastron epoch (T) 1965.0
Argument of periastron (ω)
ρ Cap A
Mass 1.52±0.04 M
Radius 1.3[2] R
Luminosity 9[7] L
Surface gravity (log g) 4.02±0.03 cgs
Temperature 6,911±63 K
Metallicity [Fe/H] −0.20±0.05 dex
Rotational velocity (v sin i) 87.7[8] km/s
Age 1.74±0.15 Gyr
Other designations
ρ Cap, 11 Cap, ADS 13887, BD−18° 5689, Gl 791.1, HD 194943, HIP 101027, HR 7822, SAO 163614, WDS J20289-1749AB[9]
Database references
ρ Cap A
ρ Cap B
ρ Cap B

Rho Capricorni (ρ Cap, ρ Capricorni) is a binary star[3] in the constellation Capricornus. Sometimes, this star is called by the name Bos, meaning the cow in Latin.[10] In Chinese, 牛宿 (Niú Su), meaning Ox (asterism), refers to an asterism consisting of β Capricorni, α2 Capricorni, ξ2 Capricorni, π Capricorni, ο Capricorni and ρ Capricorni.[11] Consequently, ρ Capricorni itself is known as 牛宿六 (Niú Su liù, English: the Sixth Star of Ox.)[12]

This system is visible to the naked eye with a combined apparent visual magnitude of +4.78.[2] The pair orbit each other with a period of 278 years and an eccentricity of 0.91.[3] Based upon an annual parallax shift of 33.04 mas as seen from the Earth,[1] the system is located about 99 light years from the Sun. It is a thin disk population[6] star system that made its closest approach to the Sun about 1.6 million years ago when it came within 12.49 ly (3.830 pc).[13]

The primary member, component A, is a yellow-white hued, F-type subgiant with an apparent magnitude of 4.97[3] and a stellar classification of F2 IV.[2] This star has 1.5[6] times the mass of the Sun and 1.3 times the Sun's radius. It is radiating 9 times[7] as much luminosity of the Sun from its outer atmosphere at an effective temperature of 6,911 K.[6] The companion, component B, has a visual magnitude of 6.88.[3]


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d e Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M. 
  3. ^ a b c d e f Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, retrieved 2017-05-12 
  4. ^ a b Cvetkovic, Z.; Ninkovic, S. (June 2010), "On the Component Masses of Visual Binaries", Serbian Astronomical Journal, 180: 71–80, Bibcode:2010SerAJ.180...71C, doi:10.2298/SAJ1080071C. 
  5. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W. 
  6. ^ a b c d Ramírez, I.; et al. (September 2012), "Lithium Abundances in nearby FGK Dwarf and Subgiant Stars: Internal Destruction, Galactic Chemical Evolution, and Exoplanets", The Astrophysical Journal, 756 (1): 46, arXiv:1207.0499Freely accessible, Bibcode:2012ApJ...756...46R, doi:10.1088/0004-637X/756/1/46. 
  7. ^ a b McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427: 343, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x. 
  8. ^ Schröder, C.; et al. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo", Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377. 
  9. ^ "rho Cap -- Double or multiple star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-05-12. 
  10. ^ "Bos", constellationsofwords.com, retrieved 2017-05-12. 
  11. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  12. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 13 日
  13. ^ Bailer-Jones, C. A. L. (March 2015), "Close encounters of the stellar kind", Astronomy & Astrophysics, 575: 13, arXiv:1412.3648Freely accessible, Bibcode:2015A&A...575A..35B, doi:10.1051/0004-6361/201425221, A35.