Zeta Ceti

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Zeta Ceti
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cetus
Right ascension  01h 51m 27.63482s[1]
Declination −10° 20′ 06.1289″[1]
Apparent magnitude (V) 3.742[2]
Spectral type K0 III Ba0.1[3]
U−B color index +1.076[2]
B−V color index +1.131[2]
Variable type Suspected[4]
Radial velocity (Rv)+10.86±0.64[5] km/s
Proper motion (μ) RA: +40.80[1] mas/yr
Dec.: −37.25[1] mas/yr
Parallax (π)13.88 ± 0.57[1] mas
Distance235 ± 10 ly
(72 ± 3 pc)
Absolute magnitude (MV)−0.54[6]
Period (P)1,652 d
Eccentricity (e)0.59
Longitude of the node (Ω)85°
Periastron epoch (T)2414377 JD
Semi-amplitude (K1)
3.3 km/s
ζ Cet A
Mass2.34[8] M
Radius25 R
Luminosity240 L
Surface gravity (log g)2.4 cgs
Temperature4,581±14 K
Metallicity [Fe/H]−0.13 dex
Rotational velocity (v sin i)3.2 km/s
Age1.24[8] Gyr
Other designations
ζ Cet, 55 Cet, BD−11° 359, FK5 62, HD 11353, HIP 8645, HR 539, SAO 148059, WDS J01515-1020A.[9]
Database references

Zeta Ceti (ζ Ceti, abbreviated Zeta Cet, ζ Cet) is a binary star in the equatorial constellation of Cetus. It has a combined apparent visual magnitude of 3.74,[2] which is bright enough to be seen with the naked eye. Based upon parallax measurements taken during the Hipparcos mission, it is approximately 235 light-years from the Sun.[1]

Zeta Ceti is the primary or 'A' component of a double star system designated WDS J01515-1020 (the secondary or 'B' component is HD 11366).[10] Zeta Ceti's two components are therefore designated WDS J01515-1020 Aa and Ab. Aa is officially named Baten Kaitos /ˈbtən ˈktɒs/, the traditional name of the entire system.[11][12]


ζ Ceti (Latinised to Zeta Ceti) is the binary pair's Bayer designation. WDS J01515-1020 A is its designation in the Washington Double Star Catalog; the designations of the two components as WDS J01515-1020 Aa and Ab derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]

It bore the traditional name Baten Kaitos, derived from the Arabic بطن قيطس batn qaytus "belly of the sea monster". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars; the WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[15] It approved the name Baten Kaitos for the component WDS J01515-1020 Aa on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[12]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Rabah al Naamat رابع ألنعامة raabi3 al naʽāmāt, which was translated into Latin as Quarta Struthionum, meaning "the fourth ostrich";[16] this star, along with Eta Ceti (Deneb Algenubi), Theta Ceti (Thanih Al Naamat), Tau Ceti (Thalath Al Naamat), and Upsilon Ceti, formed Al Naʽāmāt ('ألنعامة), "the Hen Ostriches".[17][18]

In Chinese, 天倉 (Tiān Cāng), meaning Square Celestial Granary, refers to an asterism consisting of Zeta Ceti, Iota Ceti, Theta Ceti, Eta Ceti, Tau Ceti and 57 Ceti.[19] Consequently, the Chinese name for Zeta Ceti itself is 天倉四 (Tiān Cāng sì, English: the Second Star of Square Celestial Granary).[20]


Zeta Ceti is a single-lined spectroscopic binary system with an orbital period of 4.5 years and an eccentricity of 0.59.[7] The primary, Baten Kaitos, is an evolved K-type giant star with a stellar classification of K0 III Ba0.1.[3] The suffix notation indicates this is a weak barium star, showing slightly stronger than normal lines of singly-ionized barium;[3] this star has an estimated 2.34 times the mass of the Sun and, at an estimated age of 1.24 billion years,[8] has expanded to 25 times the Sun's radius.[5]

HD 11366 (WDS J01515-1020B), of spectral type K0 III, is further away (419 parsecs, compared to WDS J01515-1020A's 72 parsecs), and is therefore not a member of the system but a chance alignment - this is referred to as an optical companion.[21]


  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:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants", Monthly Notices of the Royal Astronomical Society, 172: 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667.
  3. ^ a b c Lu, Phillip K. (1991), "Taxonomy of barium stars", Astronomical Journal, 101: 2229, Bibcode:1991AJ....101.2229L, doi:10.1086/115845.
  4. ^ Samus, N. N.; Durlevich, O. V.; et al. (2007), Combined General Catalogue of Variable Stars (GCVS4.2), retrieved 2016-09-30.
  5. ^ a b c Massarotti, Alessandro; et al. (January 2008), "Rotational and radial velocities for a sample of 761 HIPPARCOS giants and the role of binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  6. ^ 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.
  7. ^ a b Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  8. ^ a b c Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, 88.
  9. ^ "zet Cet -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-02-04.
  10. ^ "Washington Double Star Catalog". United States Naval Observatory. Retrieved 23 February 2018.
  11. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  12. ^ a b "Naming Stars". IAU.org. Retrieved 24 February 2018.
  13. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  15. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  16. ^ Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
  17. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc., p. 162, ISBN 0-486-21079-0, retrieved 2010-12-12.
  18. ^ Eta Ceti as Aoul al Naamat or Prima Struthionum (the first ostrich), Theta Ceti as Thanih al Naamat or Secunda Struthionum (the second ostrich), Tau Ceti as Thalath al Naamat or Tertia Struthionum (the third ostrich), and Zeta Ceti as Rabah al Naamat or Quarta Struthionum (the fourth ostrich). Upsilon Ceti should be Khamis al Naamat or Quinta Struthionum (the fifth ostrich) consistently, but Al Achsasi Al Mouakket designated the title "the fifth ostrich"' to Gamma Andromedae for reasons that are unclear.
  19. ^ (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.
  20. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived August 11, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  21. ^ "HD 11366". Retrieved 2018-09-23.