Rho Capricorni

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, the Chinese name for ρ Capricorni itself is 牛宿六 (Niú Su liù, English: the Sixth Star of Ox.)^[12]

Rho Capricorni

Location of ρ Capricorni (circled)
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]
Characteristics
Spectral type	F2 IV[2] + G1[4]
Astrometry
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 mas[1]
Distance	99 ± 1 ly (30.3 ± 0.4 pc)
Absolute magnitude (MV)	2.52 + 4.56[4]
Orbit[3]
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) (secondary)	144.5°
Details[6]
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
SIMBAD	ρ Cap
	ρ Cap A
	ρ Cap B
ARICNS	ρ Cap A
	ρ Cap B

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] The mass ratio is 0.539, meaning the secondary is only 53.9% as massive as the primary.^[14]

References

1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
2. 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. Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, archived from the original on 2005-04-24, retrieved 2017-05-12
4. Cvetkovic, Z.; Ninkovic, S. (June 2010), "On the Component Masses of Visual Binaries", Serbian Astronomical Journal, 180 (180): 71–80, Bibcode:2010SerAJ.180...71C, doi:10.2298/SAJ1080071C.
5. Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
6. 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:1207.0499, Bibcode:2012ApJ...756...46R, doi:10.1088/0004-637X/756/1/46, S2CID 119199829.
7. McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–357, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
8. Schröder, C.; Reiners, Ansgar; Schmitt, Jürgen H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377^{[permanent dead link‍]}
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. (in 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. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 13 日 Archived 2011-05-22 at the Wayback Machine
13. Bailer-Jones, C. A. L. (March 2015), "Close encounters of the stellar kind", Astronomy & Astrophysics, 575: 13, arXiv:1412.3648, Bibcode:2015A&A...575A..35B, doi:10.1051/0004-6361/201425221, S2CID 59039482, A35.
14. Makarov, Valeri V.; Fabricius, Claus (2021). "Astrometric Mass Ratios of 248 Long-period Binary Stars Resolved in Hipparcos and Gaia EDR3". The Astronomical Journal. 162 (6): 260. arXiv:2109.11951. Bibcode:2021AJ....162..260M. doi:10.3847/1538-3881/ac2ee0. S2CID 237635330.