Epoch J2000 Equinox J2000
|Right ascension||22h 28m 49.90685s|
|Declination||–00° 01′ 11.7942″|
|Apparent magnitude (V)||3.65 (4.42/4.51)|
|Spectral type||F3 V + F6 IV|
|U−B color index||–0.01|
|B−V color index||+0.40|
|Radial velocity (Rv)||+24.9/+28.9 km/s|
|Proper motion (μ)||RA: +182.92 mas/yr
Dec.: +50.36 mas/yr
|Parallax (π)||35.50 ± 1.26 mas|
|Distance||92 ± 3 ly
(28.2 ± 1.0 pc)
|Absolute magnitude (MV)||1.15|
|ζ Aqr A|
|Metallicity [Fe/H]||–0.13 dex|
|Rotational velocity (v sin i)||62 km/s|
|ζ Aqr B|
|Rotational velocity (v sin i)||56 km/s|
|Companion||ζ Aquarii B|
|Period (P)||587.18 ± 1.09 yr|
|Semi-major axis (a)||3.847 ± 0.147"|
|Eccentricity (e)||0.40 ± 0.01|
|Inclination (i)||138.2 ± 0.2°|
|Longitude of the node (Ω)||129.8 ± 0.3°|
|Periastron epoch (T)||1957.6|
|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.|
Zeta Aquarii (ζ Aquarii, ζ Aqr) is the Bayer designation for a binary, or possibly a triple star system; the central star of the "water jar" asterism in the equatorial constellation of Aquarius. The combined apparent visual magnitude of this system is 3.65, which is readily visible to the naked eye. Parallax measurements yield a distance estimate of around 92 light-years (28 parsecs) from Earth.
Zeta Aquarii has the traditional name Sadaltager (or Altager), from the Arabic سعد التاجر sa‘d al-tājir "luck of the merchant". 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). This star, along with γ Aqr (Sadachbia), π Aqr (Seat) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.
In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of ζ Aquarii, γ Aquarii, η Aquarii and π Aquarii. Consequently, ζ Aquarii itself is known as 墳墓一 (Fén Mù yī, English: the First Star of Tomb.)
Christian Mayer, director of the Mannheim Observatory, is considered the first to have observed Zeta Aquarii to be double, in 1777. A couple of years later, William Herschel also discovered this duality. 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.
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. The fact that their brightness is so similar makes the pair easy to measure and resolve.
ζ Aquarii B is a suspected astrometric binary system with a 25.8 year orbital period and a semimajor axis of 10.8 astronomical units. If this is confirmed, then the smaller companion may be a red dwarf with a classification of M0 V and 40% of the Sun's mass.
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- γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), π Aqr as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and ζ Aqr as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). η Aqr should be designated as al Achbiya consistently, but it was not designated as the Arabian name except the name Hydria (Greek) or Deli (Hebrew)
- (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.
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- Double Stars to Follow, Part IV: Zeta Aquarii and Mu Cygni. by Martin Gaskell, Prairie Astronomy Club Home Page.
- "This Month's Double Stars" by Richard Jaworski.
- Image ζ Aquarii