Zeta Capricorni

Zeta Capricorni, Latinized from ζ Capricorni, is a binary star system in the southern constellation of Capricornus. It is visible to the naked eye with an apparent visual magnitude of 3.77.[2] The system is located at a distance of approximately 386 light years from the Sun based on parallax.[1] It is drifting further away with a radial velocity of +2 km/s. The absolute magnitude of this system is −1.59.[2]

Zeta Capricorni
Location of ζ Capricorni (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Capricornus
Right ascension 21h 26m 40.02634s[1]
Declination −22° 24′ 40.8042″[1]
Apparent magnitude (V) 3.77[2]
Characteristics
Spectral type G4Ib: Ba2[3] + DA2.2[4]
U−B color index +0.57[5]
B−V color index +0.99[5]
Variable type Suspected eclipsing binary[6][7]
Astrometry
Radial velocity (Rv)+2.1±0.1[2] km/s
Proper motion (μ) RA: −2.23[1] mas/yr
Dec.: 18.10[1] mas/yr
Parallax (π)8.46 ± 0.21[1] mas
Distance386 ± 10 ly
(118 ± 3 pc)
Absolute magnitude (MV)−1.59[2]
Orbit[8]
Period (P)2,378.2 d
Semi-major axis (a)8.56±4.3 mas
1.00+1.69
−0.44 AU
Eccentricity (e)0.2821
Inclination (i)111.7±20.7°
Longitude of the node (Ω)190.7±50.0°
Periastron epoch (T)2,445,996 JD
Argument of periastron (ω)
(secondary)		233.8±19.8°
Details[9]
A
Mass4.5+0.3
−0.2 M☉
Radius~29[10] R☉
Luminosity561+180
−143 L☉
Surface gravity (log g)1.7±0.3 cgs
Temperature5,269±53 K
Metallicity [Fe/H]−0.09 dex
B
Mass1.03 M☉
Temperature23,000[4] K
Other designations
ζ Cap, 34 Cap, NSV 25596, CD−22°15388, GC 30020, HD 204075, HIP 105881, HR 8204, SAO 190341, CCDM J21267-2225AB, WDS J21267-2225AB, WD 2123-226[11]
Database references
SIMBADdata

Properties

The binary nature of this system was announced in 1980 by Erika Böhm-Vitense based on an ultraviolet excess attributed to a white dwarf companion.[12] It is a single-lined spectroscopic binary system.[13] Based on an incomplete orbital arc, the orbital period for this system is 6.5 years and the eccentricity (ovalness) is 0.28.[8] It was flagged as a suspected eclipsing binary in 1988 due to observed variations in the light curve.[6][7]

The primary, designated component A, has a stellar classification of G4Ib: Ba2.[3] This notation indicates this is a yellow-hued supergiant star, although the ':' means there is some uncertainty about the class. The temperature and surface gravity of this object suggests it may be a horizontal-branch star.[14] It is considered a prototypical example of a Barium star,[4] as indicated by the 'Ba2' class suffix. The properties of these objects include overabundances of carbon molecules (such as C2) and s-process elements.[13] Zeta Capricorni has an overabundance of the s-process element praseodymium.[15][16]

Its companion, component B, is a carbon-oxygen white dwarf[17] with a hydrogen-rich atmosphere and a class of DA2.2.[4] It is about as massive as the Sun, and its temperature is 23,000 K. In the course of its evolution, the progenitor star passed through the thermally-pulsing asymptotic giant branch, during which the enlarged atmosphere transferred material to the primary.[4] The abundance of niobium in the primary's atmosphere, a product of the decay of zirconium-93, is at a level that suggests the transfer to the primary took place more than three million years ago.[18]

A magnitude 12.5 visual companion[10] was discovered by T. J. J. See in 1897. As of 1997, it was located at an angular separation of 17.30″ along a position angle of 12°.[19]

Chinese Name

In Chinese, 十二國 (Shíer Guó), meaning Twelve States, refers to an asterism which represents twelve ancient states in the Spring and Autumn period and the Warring States period, consisting of ζ Capricorni, φ Capricorni, ι Capricorni, 38 Capricorni, 35 Capricorni, 36 Capricorni, χ Capricorni, θ Capricorni, 30 Capricorni, 33 Capricorni, 19 Capricorni, 26 Capricorni, 27 Capricorni, 20 Capricorni, η Capricorni and 21 Capricorni.[20] Consequently, the Chinese name for ζ Capricorni itself represents the state of Yan (燕).,[21] together with ν Ophiuchi in Left Wall of Heavenly Market Enclosure (asterism).[22]

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. Vizier catalog entry
  2. 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.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
  4. Holberg, J. B.; et al. (2013). "Where are all the Sirius-like binary systems?". Monthly Notices of the Royal Astronomical Society. 435 (3): 2077. arXiv:1307.8047. Bibcode:2013MNRAS.435.2077H. doi:10.1093/mnras/stt1433.
  5. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. SIMBAD. Bibcode:1986EgUBV........0M.
  6. Srivastava, R. K. (July 1988). "Eclipsing Binary Signatures in zeta Capricorni". Information Bulletin on Variable Stars. 3217: 1. Bibcode:1988IBVS.3217....1S.
  7. Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  8. Pourbaix, D. (2000). "Re-processing the Hipparcos Transit Data and Intermediate Astrometric Data of spectroscopic binaries. I. Ba, CH and Tc-poor S stars". Astronomy and Astrophysics Supplement. 145: 161–183. arXiv:astro-ph/0006175. Bibcode:2000A&AS..145..161P. doi:10.1051/aas:2000346.
  9. Jorissen, A.; et al. (June 2019). "Barium and related stars, and their white-dwarf companions. I. Giant stars". Astronomy & Astrophysics. 626: 28. arXiv:1904.03975. Bibcode:2019A&A...626A.127J. doi:10.1051/0004-6361/201834630. A127.
  10. Kaler, James B. "ZETA CAP (Zeta Capricorni)". Stars. Retrieved 30 December 2016.
  11. "zet Cap". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 December 2016.
  12. Boehm-Vitense, E. (July 1980). "The white dwarf companion of the barium star ZET Cap". Astrophysical Journal. 239: L79–L83. Bibcode:1980ApJ...239L..79B. doi:10.1086/183296.
  13. Smith, V. V.; et al. (December 1980). "A spectrum analysis of the bright barium star ZET Cap". Publications of the Astronomical Society of the Pacific. 92: 809–818. Bibcode:1980PASP...92..809S. doi:10.1086/130755.
  14. de Castro, D. B.; et al. (July 2016). "Chemical abundances and kinematics of barium stars". Monthly Notices of the Royal Astronomical Society. 459 (4): 4299–4324. arXiv:1604.03031. Bibcode:2016MNRAS.459.4299D. doi:10.1093/mnras/stw815.
  15. Warner, B. (1965). "The barium stars". Monthly Notices of the Royal Astronomical Society. 129 (3): 263. Bibcode:1965MNRAS.129..263W. doi:10.1093/mnras/129.3.263.
  16. Allen, M. S.; Cowley, C. R. (1974). "Resolution of the praseodymium abundance anomaly in the Ba II stars". The Astrophysical Journal. 190: 601. Bibcode:1974ApJ...190..601A. doi:10.1086/152917.
  17. Merle, T.; et al. (February 2016). "To Ba or not to Ba: Enrichment in s-process elements in binary systems with WD companions of various masses". Astronomy & Astrophysics. 586: 16. arXiv:1510.05908. Bibcode:2016A&A...586A.151M. doi:10.1051/0004-6361/201526944. A151.
  18. Smith, V. V.; Lambert, D. L. (March 1984). "Niobium and rubidium in the barium star zeta Capricorni". Publications of the Astronomical Society of the Pacific. 96: 226–230. Bibcode:1984PASP...96..226S. doi:10.1086/131325.
  19. Mason, B. D.; et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  20. (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.
  21. Richard Hinckley Allen: Star Names — Their Lore and Meaning: Capricornus
  22. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 23 日
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