Astronomy:Eta Hydrae

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Short description: Star in the constellation Hydra
η Hydrae
Hydra constellation map.svg
Red circle.svg
Location of η Hydrae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Hydra
Right ascension  08h 43m 13.47499s[1]
Declination +03° 23′ 55.1867″[1]
Apparent magnitude (V) 4.294[2]
Characteristics
Spectral type B3 V[3]
U−B color index −0.726[2]
B−V color index −0.187[2]
Variable type Candidate β Cep[4]
Astrometry
Proper motion (μ) RA: −19.39[1] mas/yr
Dec.: −1.08[1] mas/yr
Parallax (π)5.56 ± 0.24[1] mas
Distance590 ± 30 ly
(180 ± 8 pc)
Absolute magnitude (MV)−1.48[5]
Details
Mass7.0±0.1[6] M☉
Radius3.9[7] R☉
Luminosity (bolometric)2,680[8] L☉
Surface gravity (log g)3.933[9] cgs
Temperature18,630±411[9] K
Rotational velocity (v sin i)101±5[9] km/s
Age31.6±3.9[6] Myr
Other designations
η Hya, 7 Hydrae, BD+03°2039, FK5 2687, HD 74280, HIP 42799, HR 3454, SAO 117050[10]
Database references
SIMBADdata

Eta Hydrae (η Hydrae) is a star in the equatorial constellation of Hydra. With an apparent visual magnitude of 4.3,[2] it is visible to the naked eye. However, it is the faintest of the five stars that form the "head" of the hydra.[11] Based upon an annual parallax shift of 5.56 mas,[1] it is located roughly 590 light years from the Sun.

A light curve for Eta Hydrae, plotted from TESS data[12]

This is a B-type main sequence star with a stellar classification of B3V.[3] It has been classified as a candidate Beta Cephei variable with a period of 2.2 days, although this designation was rejected by Stankov and Handler (2005).[4] The spectrum shows a slight underabundance of carbon, compared to the Sun.[13] The star is around 32[6] million years old and is spinning with a projected rotational velocity of 101[9] km/s. It has an estimated seven[6] times the mass of the Sun and nearly four[7] times the Sun's radius. Eta Hydrae radiates 2,680[8] times the solar luminosity from its outer atmosphere at an effective temperature of 18,630[9] K.

Name and etymology

This star, along with δ Hya (Lisan al Sudja), ε Hya, ζ Hya, ρ Hya and σ Hya (Minchir), were Ulug Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".[14] 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).[15]

In Chinese, 柳宿 (Liǔ Sù), meaning Willow, refers to an asterism consisting of η Hydrae, δ Hydra, σ Hydrae, ρ Hydrae, ε Hydrae, ζ Hydrae, ω Hydrae and θ Hydrae[16] Consequently, η Hydrae itself is known as 柳宿三 (Liǔ Sù sān, English: the Third Star of Willow).[17]

The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, δ Hya (Lisan al Sudja), ε Hya, ζ Hya, ρ Hya and σ Hya (Minchir).[18]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 2.2 2.3 Oja, T. (August 1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series 65 (2): 405–409, Bibcode: 1986A&AS...65..405O. 
  3. ↑ 3.0 3.1 Levenhagen, R. S.; Leister, N. V. (2006), "Spectroscopic Analysis of Southern B and Be Stars", Monthly Notices of the Royal Astronomical Society 371 (1): 252–62, doi:10.1111/j.1365-2966.2006.10655.x, Bibcode: 2006MNRAS.371..252L. 
  4. ↑ 4.0 4.1 Stankov, Anamarija; Handler, Gerald (June 2005), "Catalog of Galactic β Cephei Stars", The Astrophysical Journal Supplement Series 158 (2): 193–216, doi:10.1086/429408, Bibcode: 2005ApJS..158..193S. 
  5. ↑ Ammler-von Eiff, Matthias; Reiners, Ansgar (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics 542: A116, doi:10.1051/0004-6361/201118724, Bibcode: 2012A&A...542A.116A. 
  6. ↑ 6.0 6.1 6.2 6.3 Tetzlaff, N. et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T. 
  7. ↑ 7.0 7.1 Pasinetti Fracassini, L. E. et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics 367: 521–524, doi:10.1051/0004-6361:20000451, Bibcode: 2001A&A...367..521P. 
  8. ↑ 8.0 8.1 Hohle, M. M. et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, doi:10.1002/asna.200911355, Bibcode: 2010AN....331..349H. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Huang, W.; Gies, D. R. (August 2008), "Stellar Rotation in Field and Cluster B Stars", The Astrophysical Journal 683 (2): 1045–1051, doi:10.1086/590106, 1045−1051, Bibcode: 2008ApJ...683.1045H. 
  10. ↑ "eta Hya". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eta+Hya. 
  11. ↑ Moore, Patrick (2013), The Observer's Year: 366 Nights of the Universe, The Patrick Moore Practical Astronomy Series, Springer Science & Business Media, p. 79, ISBN 978-1447136132, https://books.google.com/books?id=p87TBwAAQBAJ&pg=PA71-IA1. 
  12. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  13. ↑ Schnerr, R. S. et al. (June 2008), "Magnetic field measurements and wind-line variability of OB-type stars", Astronomy and Astrophysics 483 (3): 857–867, doi:10.1051/0004-6361:20077740, Bibcode: 2008A&A...483..857S. 
  14. ↑ 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, https://archive.org/details/starnamestheirlo00alle/page/249, retrieved 2010-12-12 
  15. ↑ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology, https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720005197_1972005197.pdf 
  16. ↑ (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.
  17. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日
  18. ↑ Selin, Helaine, ed. (1997), Encyclopaedia of the history of science, technology, and medicine in non-western cultures, Dordrecht: Kluwer Academic Publishers, p. 105, ISBN 9780792340669, https://books.google.com/books?id=raKRY3KQspsC 



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