Zeta Aquarii

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Zeta Aquarii A/B
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of ζ Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 22h 28m 49.90685s[1]
Declination –00° 01′ 11.7942″[1]
Apparent magnitude (V) 3.65[2] (4.42 / 4.51)[3]
Spectral type F3 V + F6 IV[3]
U−B color index –0.01[2]
B−V color index +0.40[2]
Radial velocity (Rv) +24.9/+28.9[4] km/s
Proper motion (μ) RA: +182.92[1] mas/yr
Dec.: +50.36[1] mas/yr
Parallax (π) 35.50 ± 1.26[1] mas
Distance 92 ± 3 ly
(28.2 ± 1.0 pc)
Absolute magnitude (MV) 1.15[5]
Primary ζ Aqr Aa
Companion ζ Aqr Ab
Period (P) 25.95 ± 0.048 yr
Semi-major axis (a) 0.385″
Eccentricity (e) 0.872 ± 0.006
Inclination (i) 11.8 ± 6.7°
Longitude of the node (Ω) 293.7 ± 74°
Periastron epoch (T) B 2006.52 ± 0.13
Argument of periastron (ω)
100.9 ± 73°
Primary ζ Aqr A
Companion ζ Aqr B
Period (P) 540 ± 15 yr
Semi-major axis (a) 3.496 ± 0.046″
Eccentricity (e) 0.419 ± 0.011
Inclination (i) 142.0 ± 0.4°
Longitude of the node (Ω) 131.3 ± 0.8°
Periastron epoch (T) B 1981.50 ± 0.58
Argument of periastron (ω)
269.3 ± 1.7°
ζ Aqr A
Mass 1.4 / 0.6[7] M
Metallicity [Fe/H] –0.13[5] dex
Rotational velocity (v sin i) 62[8] km/s
Age 1.0[5] Gyr
ζ Aqr B
Mass 1.4[7] M
Rotational velocity (v sin i) 56[8] km/s
Other designations
55 Aquarii, ADS 15971, BD−00°4365, HIP 110960.
ζ Aqr A: ζ2 Aquarii, Zeta2 Aquarii, HD 213052, HR 8559, SAO 146108.
ζ Aqr B: ζ1 Aquarii, Zeta1 Aquarii, HD 213051, HR 8558, SAO 146107.
Database references
ζ Aqr A
ζ Aqr B

Zeta Aquarii (ζ Aquarii, ζ Aqr) is the Bayer designation for a binary, or possibly a triple star system;[3] the central star of the "water jar" asterism[9] in the equatorial constellation of Aquarius. The combined apparent visual magnitude of this system is 3.65,[2] which is readily visible to the naked eye. Parallax measurements yield a distance estimate of around 92 light-years (28 parsecs) from Earth.[1]


In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Achr al Achbiya (أجر ألأجبية - akhir al ahbiyah), which was translated into Latin as Postrema Tabernaculorum, meaning the end of luck of the homes (tents).[10] This star, along with γ Aqr (Sadachbia), π Aqr (Seat) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.[11][12]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of ζ Aquarii, γ Aquarii, η Aquarii and π Aquarii.[13] Consequently, ζ Aquarii itself is known as 墳墓一 (Fén Mù yī, English: the First Star of Tomb.)[14]


Christian Mayer, director of the Mannheim Observatory, is considered the first to have observed Zeta Aquarii to be double, in 1777.[citation needed] A couple of years later, William Herschel also discovered this duality.[citation needed] The two stars have an orbital period of about 587 years. The semimajor axis is 3.8 arcseconds and they have an orbital eccentricity of 0.40. The orbital plane is inclined by 138.2° to the line of sight.[15]

The brighter component, ζ Aquarii A (also called ζ2 Aquarii), is a yellow-white-hued F-type main sequence star with an apparent magnitude of +4.42. Its companion, ζ Aquarii B (also called ζ1 Aquarii), is a yellow-white-hued F-type subgiant with an apparent magnitude of +4.51.[3] The fact that their brightness is so similar makes the pair easy to measure and resolve.

Zeta Aquarii B is known to be an astrometric binary system, as it undergoes regular perturbations from its orbit. It has a 26-year orbital period and a semimajor axis of 0.11″. The secondary's mass is 0.6 M.[7]

Zeta Aquarii is currently a northern hemisphere object. In 2004 it was directly above the celestial equator, and before that it was located south of it.[citation needed]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752Freely accessible, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Nicolet, B. (1978). "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System". Astronomy and Astrophysics Supplement Series. 34: 1–49. Bibcode:1978A&AS...34....1N. 
  3. ^ a b c d Tokovinin, A.; et al. (December 2010), "High-Resolution Imaging at the SOAR Telescope", Publications of the Astronomical Society of the Pacific, 122 (898): 1483–1494, Bibcode:2010PASP..122.1483T, arXiv:1010.4176Freely accessible, doi:10.1086/657903. 
  4. ^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W. 
  5. ^ a b c Nordström, B.; et al. (May 2004), "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs", Astronomy and Astrophysics, 418 (3): 989–1019, Bibcode:2004A&A...418..989N, arXiv:astro-ph/0405198Freely accessible, doi:10.1051/0004-6361:20035959. 
  6. ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 14 June 2017. 
  7. ^ a b c d Tokovinin, Andrei (2016). "The Triple System Zeta Aquarii". The Astrophysical Journal. 831 (2): 151. Bibcode:2016ApJ...831..151T. arXiv:1608.08564Freely accessible. doi:10.3847/0004-637X/831/2/151. 
  8. ^ a b Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1), Bibcode:1970CoAsi.239....1B. 
  9. ^ Dibon-Smith, Richard, "z Aquarii", The Constellations Web Page, retrieved 2012-07-10. 
  10. ^ 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 (8): 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429. 
  11. ^ Davis Jr., G. A. (October 1944), "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names", Popular Astronomy, 52 (3): 12, Bibcode:1944PA.....52....8D. 
  12. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 52, ISBN 0-486-21079-0, retrieved 2010-12-12. 
  13. ^ (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.
  14. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
  15. ^ Olevic, D.; Cvetkovic, Z. (2004), "Orbits of 6 Binaries", Serbian Astronomical Journal, 168 (168): 25, Bibcode:2004SerAJ.168...25O, doi:10.2298/saj0468025o. 

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