Location of ζ Aquarii (circled) | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22 28 49.90685 |
| Declination | –00° 01′ 11.7942″ |
| Apparent magnitude (V) | 3.65 (4.42 / 4.51) |
| Characteristics | |
| Spectral type | F3 V + F6 IV |
| U−B color index | –0.01 |
| B−V color index | +0.40 |
| Astrometry | |
| 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 |
| Orbit | |
| 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) (secondary) | 100.9 ± 73° |
| Orbit | |
| 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) (secondary) | 269.3 ± 1.7° |
| Details | |
| ζ Aqr A | |
| Mass | 1.4 / 0.6 M☉ |
| Metallicity | –0.13 dex |
| Rotational velocity (v sin i) | 62 km/s |
| Age | 1.0 Gyr |
| ζ Aqr B | |
| Mass | 1.4 M☉ |
| Rotational velocity (v sin i) | 56 km/s |
| Other designations | |
| 55 Aquarii, ADS 15971, BD−00°4365, HIP 110960. | |
| ζ Aqr A: ζ Aquarii, Zeta Aquarii, HD 213052, HR 8559, SAO 146108. | |
| ζ Aqr B: ζ Aquarii, Zeta Aquarii, HD 213051, HR 8558, SAO 146107. | |
| Database references | |
| SIMBAD | ζ Aqr |
| ζ Aqr A | |
| ζ Aqr B | |
Zeta Aquarii (ζ Aquarii, ζ Aqr) is the Bayer designation for 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.
Etymology
In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Achr al Achbiya (آخر ألأخبية - ākhir al-akhbiya), 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-Akḣbiya (الأخبية), the Tents.
In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of ζ Aquarii, γ Aquarii, η Aquarii and π Aquarii. Consequently, the Chinese name for ζ Aquarii itself is 墳墓一 (Fén Mù yī, English: the First Star of Tomb.)
Properties
Orbits
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.
Spectral class and stellar mass
The brighter component, ζ Aquarii A (also called ζ 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 ζ 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.
Zeta Aquarii A 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☉.
Observational history
The binary was measured by William Herschel in 1779; however, Christian Mayer listed an earlier observation in his first double-star catalog in 1784, so it is not known who first identified Zeta Aquarii as a binary star system.
Photographic measurements available since the early 20th century were more precise than earlier micrometer estimates, and they revealed regular orbital deviations in the Zeta Aquarii system. Kaj Aage Gunnar Strand in 1942 was the first to note this pattern and identify Zeta Aquarii as a triple star system. Several other astronomers later published revised models of the system's orbits.
At first, Strand and the other astronomers assumed that the third star (which had still not been observed directly) was in orbit around Zeta Aquarii B. The first claimed direct images of this third star were in 1979, by Ebersberger and Weigelt (who claimed that it revolved around Zeta Aquarii A instead), and then in 1982 by McCarthy et al., who again attributed it to Zeta Aquarii B. In a 1984 paper, Wulff-Dieter Heintz dismissed both claims as bogus and proposed a new orbital model, demonstrating that the third star revolved around Zeta Aquarii A. (According to Andrei Tokovinin, the imaging technology available at the time would not have been capable of producing an image of the third star.) This third star, now known as Zeta Aquarii Ab, was not directly imaged until 2009, by the Southern Astrophysical Research Telescope. Initially, the third star was attributed to Zeta Aquarii B, but later observations (such as Hartkopf et al. in 2012) "securely" identified it with Zeta Aquarii A instead.
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.
References
- ^ van Leeuwen, F. (November 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.
- ^ 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.
- ^ 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, arXiv:1010.4176, Bibcode:2010PASP..122.1483T, doi:10.1086/657903, S2CID 26826524.
- Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
- ^ 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, arXiv:astro-ph/0405198, Bibcode:2004A&A...418..989N, doi:10.1051/0004-6361:20035959, S2CID 11027621.
- "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 14 June 2017.
- ^ Tokovinin, Andrei (2016). "The Triple System Zeta Aquarii". The Astrophysical Journal. 831 (2): 151. arXiv:1608.08564. Bibcode:2016ApJ...831..151T. doi:10.3847/0004-637X/831/2/151. S2CID 118734938.
- ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1): 1, Bibcode:1970CoAsi.239....1B.
- Dibon-Smith, Richard, "z Aquarii", The Constellations Web Page, retrieved 2012-07-10.
- 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.
- 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.
- Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 52, ISBN 978-0-486-21079-7, retrieved 2010-12-12.
- (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.
- (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日 Archived 2011-05-22 at the Wayback Machine
- Olevic, D.; Cvetkovic, Z. (2004), "Orbits of 6 Binaries", Serbian Astronomical Journal, 168 (168): 25, Bibcode:2004SerAJ.168...25O, doi:10.2298/saj0468025o.
Further reading
- Heintz, Wulff-Dieter (1984). The Triple Star Zeta Aquarii. The Astrophysical Journal. 284: pp. 806-9. (This is Heintz's 1984 article, mentioned above as the one that established Zeta Aquarii Ab as being connected to Zeta Aquarii Aa; it was not used as a reference for this article.)
- Strand, Kaj Aage Gunnar (1942). The Orbital Motion of the Triple System Zeta Aquarii. The Astrophysical Journal. 49 (18): pp. 165-72. (This is Strand's 1942 article, mentioned above as the one that established Zeta Aquarii as a triple system; it was not used as a reference for this article.)
External links
- 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
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