Zeta Hydrae

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Zeta Hydrae
Diagram showing star positions and boundaries of the Hydra constellation and its surroundings
Cercle rouge 100%.svg

Location of ζ Hydrae (circled) near the center
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydra
Right ascension 08h 55m 23.62614s[1]
Declination +05° 56′ 44.0354″[1]
Apparent magnitude (V) 3.10[2]
Spectral type G9 II-III[3]
U−B color index +0.82[2]
B−V color index +1.00[2]
Radial velocity (Rv) +22.8[4] km/s
Proper motion (μ) RA: –100.06[1] mas/yr
Dec.: +15.46[1] mas/yr
Parallax (π) 19.51 ± 0.18[1] mas
Distance 167 ± 2 ly
(51.3 ± 0.5 pc)
Absolute magnitude (MV) –0.24[5]
Mass 4.2[6] M
Radius 17.9[7] R
Luminosity 132[7] L
Surface gravity (log g) 2.48[7] cgs
Temperature 4,925[6] K
Metallicity [Fe/H] –0.21[8] dex
Rotational velocity (v sin i) 2.5[8] km/s
Age 400[5] Myr
Other designations
16 Hydrae, BD+06 2060, FK5 334, HD 76294, HIP 43813, HR 3547, SAO 117264.[9]

Zeta Hydrae (ζ Hya, ζ Hydrae) is a solitary star in the equatorial constellation of Hydra. This is a generally faint constellation, so, at an apparent visual magnitude of +3.10,[2] this is the third-brightest member after Alphard and Gamma Hydrae. The distance to this star has been measured using the parallax technique, yielding a value of roughly 167 light-years (51 parsecs).[1] At this distance, the visual magnitude of the star is diminished by 0.03 as a result of extinction from intervening gas and dust.[5] The star Delta Hydrae is located 12.9 light-years (4.0 parsecs) from Zeta Hydrae and may be a co-moving companion.[10]

With a stellar classification of G9 II-III,[3] this is an evolved giant star that is radiating 132[7] times the luminosity of the Sun from its outer envelope at an effective temperature of 4,925 K.[6] At this heat, the star glows with the yellow hue of a G-type star.[11] The radius of this star, as measured using interferometry, is about 18 times the Sun's radius.[7] It has an estimated 4.2 times the mass of the Sun[6] and is around 400 million years old.[5]

Name and etymology[edit]

This star, along with δ Hya (Lisan al Sudja), ε Hya, η Hya, ρ Hya and σ Hya (Minhar al Shija), were Ulug Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".[12] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Min al Azʽal or Minazal were the title for five stars:δ Hya as Minazal I, η Hya as Minazal II, ε Hya as Minazal III, ρ Hya as Minazal IV and ζ Hya as Minazal V (exclude σ Hya).[13]

In Chinese, 柳宿 (Liǔ Sù), meaning Willow, refers to an asterism consisting of ζ Hydrae, δ Hydra, σ Hydrae, η Hydrae, ρ Hydrae, ε Hydrae, ω Hydrae and θ Hydrae[14] Consequently, ζ Hydrae itself is known as 柳宿六 (Liǔ Sù liù, English: the Sixth Star of Willow).[15]

The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, δ Hya (Lisan al Sudja), ε Hya, η Hya, ρ Hya and σ Hya (Minhar al Shija).[16]


  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, arXiv:0708.1752free to read, 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 Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics, 11 (1): 29–50, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333 
  4. ^ Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W 
  5. ^ a b c d Takeda, Yoichi; Sato, Bun'ei; Murata, Daisuke (August 2008), "Stellar parameters and elemental abundances of late-G giants", Publications of the Astronomical Society of Japan, 60 (4): 781–802, arXiv:0805.2434free to read, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781 
  6. ^ a b c d Ando, Hiroyasu; et al. (April 2008), "Detection of Small-Amplitude Oscillations in the G-Giant HD76294 (ξ Hydrae)", Publications of the Astronomical Society of Japan, 60 (2): 219–222, Bibcode:2008PASJ...60..219A, doi:10.1093/pasj/60.2.219 
  7. ^ a b c d e Ando, Hiroyasu; Tsuboi, Yusuke; Kambe, Eiji; Sato, Bun'ei (August 2010), "Oscillations in G-Type Giants", Publications of the Astronomical Society of Japan, 62 (4): 1117–1126, arXiv:1007.1286free to read, Bibcode:2010PASJ...62.1117A, doi:10.1093/pasj/62.4.1117 
  8. ^ a b 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 
  9. ^ "zet Hya -- Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2006-11-05 
  10. ^ Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", The Astrophysical Journal Supplement, 192 (1): 2, arXiv:1007.0425free to read, Bibcode:2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2 
  11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  12. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 249, ISBN 0-486-21079-0, retrieved 2010-12-12 
  13. ^ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology 
  14. ^ (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.
  15. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日
  16. ^ Selin, Helaine, ed. (1997), Encyclopaedia of the history of science, technology, and medicine in non-western cultures, Dordrecht: Kluwer Academic Publishers, p. 105