Kappa Hydrae

κ Hydrae, Latinised as Kappa Hydrae, is a solitary[13] star in the equatorial constellation of Hydra. Its apparent visual magnitude is 5.06,[2] which is bright enough to be faintly visible to the naked eye. The distance to this star is around 135 pc (440 ly), based upon an annual parallax shift of 7.48 mas.[1] It may be a variable star, meaning it undergoes repeated fluctuations in brightness by at least 0.1 magnitude.[5]

κ Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension  09h 40m 18.36496s[1]
Declination −14° 19′ 56.2675″[1]
Apparent magnitude (V) 5.06[2]
Characteristics
Spectral type B4 IV/V[3]
U−B color index −0.57[2]
B−V color index −0.15[2]
Variable type Suspected[4][5]
Astrometry
Radial velocity (Rv)20.6±2.0[6] km/s
Proper motion (μ) RA: −23.41[1] mas/yr
Dec.: −21.10[1] mas/yr
Parallax (π)7.48 ± 0.30[1] mas
Distance440 ± 20 ly
(134 ± 5 pc)
Absolute magnitude (MV)−0.98[7]
Details
Mass5.0±0.1[3] M☉
Radius3.4[8] R☉
Luminosity328[9] L☉
Temperature16,150±920[10] K
Rotational velocity (v sin i)115.0[11] km/s
Age30.7±3.3[3] Myr
Other designations
κ Hya, 38 Hydrae, BD−13° 2917, FK5 364, HD 83754, HIP 47452, HR 3849, SAO 155388.[12]
Database references
SIMBADdata

This is an evolving B-type star with a stellar classification of B4 IV/V,[3] having a luminosity class intermediate between a subgiant and a giant star. It has an estimated five[3] times the mass of the Sun and 3.4 times the Sun's radius.[8] Kappa Hydrae has a high rate of spin with a projected rotational velocity of 115.0 km/s,[11] and is only about 31 million years old.[3] The star radiates 328 times the solar luminosity from its outer atmosphere[9] at an effective temperature of 16,150 K.[10]

Name

This star was one of the set assigned by the 16th century astronomer Al Tizini[14] to Al Sharāsīf (ألشراسيف), the Ribs (of Hydra), which included the stars from β Crateris westward through κ Hydrae.[15][16]

According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Sharāsīf were the title for two stars : β Crateris as Al Sharasīf II and κ Hydrae as Al Sharasīf I.[17]

In Chinese, 張宿 (Zhāng Xiù), meaning Extended Net, refers to an asterism consisting of Kappa Hydrae, Upsilon1 Hydrae, Lambda Hydrae, Mu Hydrae, HD 87344, and Phi1 Hydrae.[18] Consequently, Kappa Hydrae itself is known as 張宿五 (Zhāng Xiù wǔ), "the Fifth Star of Extended Net".[19]

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References
  1. van Leeuwen, F. (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.
  2. Nicolet, B. (October 1978), "Catalogue of homogeneous data in the UBV photoelectric photometric system", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N.
  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, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  4. Samus, N. N.; Durlevich, O. V.; et al. (2009), General Catalogue of Variable Stars, 1, Bibcode:2009yCat....102025S.
  5. Rufener, F.; Bartholdi, P. (June 1982), "List of 333 variable, microvariable or suspected variable stars detected in the Geneva photometry", Astronomy and Astrophysics Supplement Series, 48: 503–511, Bibcode:1982A&AS...48..503R.
  6. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  7. Zorec, J.; Briot, D. (May 1991), "Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature", Astronomy and Astrophysics, 245 (1): 150–170, Bibcode:1991A&A...245..150Z.
  8. Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (3rd ed.), 367: 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  9. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  10. Soubiran, C.; et al. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics, 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247.
  11. Abt, Helmut A.; et al. (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590.
  12. "kap Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-01-05.
  13. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  14. Rim Turkmani. "Arabic Roots of the Scientific Revolution". Muslim Heritage. Retrieved 1 July 2016.
  15. Star Names - R.H.Allen p. 182
  16. Star Names - R.H.Allen p. 246
  17. 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.
  18. (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.
  19. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
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