Rho Hydrae
Binary star in the constellation Hydra
Rho Hydrae , equally written ρ Hydrae , is a binary star [ 9] in the equatorial constellation of Hydra . It is visible to the naked eye with an apparent visual magnitude of 4.34.[ 2] The distance to this system, based upon an annual parallax shift of 9.21 mas ,[ 1] is about 354 light years . At that distance, the visual magnitude is diminished by an interstellar extinction of 0.06 magnitudes, due to intervening dust.[ 7]
The primary component is an A-type main sequence star with a stellar classification of A0 Vn.[ 3] It has around double[ 6] the radius of the Sun and 3.2 times the Sun's mass . Rho Hydrae is around 350 million years old[ 7] and has a high rate of spin, with a projected rotational velocity of 128 km/s. It radiates 242 times the solar luminosity from its outer atmosphere at an effective temperature of 9,795 K.[ 3] The companion is a magnitude 11.9 star at an angular separation of 12.1 arc seconds along a position angle of 146°, as of 2000.[ 10]
Name and etymology
This system appears among bright stars in a compact pentagon, resembling a quadrilateral due to the suggestive proximity (close arc distance) to Epsilon Hydrae (ε Hya) . This shape in the Greco-Roman tradition, which draws on trading and navigation histories shared with nearby older-recorded astrologies is an asterism that represents the head of the water snake.[ 11]
This light source, along with comparable strength (apparent magnitude) Epsilon, δ Hya (Lisan al Sudja), ζ Hya , η Hya , and σ Hya (Minchir), 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 ρ Hydrae, δ Hydra , σ Hydrae , η Hydrae , ε Hydrae , ζ Hydrae , ω Hydrae and θ Hydrae [ 14] Consequently, ρ Hydrae itself is known as 柳宿四 (Liǔ Sù sì , English: the Fourth 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 , ζ Hya and σ Hya (Minchir).[ 16]
References
^ a b c d e f 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 , S2CID 18759600 .
^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data , SIMBAD , Bibcode :1986EgUBV........0M .
^ a b c d Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics , 537 : A120, arXiv :1201.2052 , Bibcode :2012A&A...537A.120Z , doi :10.1051/0004-6361/201117691 , S2CID 55586789 .
^ Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication , Washington: Carnegie Institution of Washington, Bibcode :1953GCRV..C......0W .
^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters , 38 (5): 331, arXiv :1108.4971 , Bibcode :2012AstL...38..331A , doi :10.1134/S1063773712050015 , S2CID 119257644 .
^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics , 367 (3rd ed.): 521–524, arXiv :astro-ph/0012289 , Bibcode :2001A&A...367..521P , doi :10.1051/0004-6361:20000451 , S2CID 425754 .
^ a b c Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters , 38 (11): 694–706, arXiv :1606.09028 , Bibcode :2012AstL...38..694G , doi :10.1134/S1063773712110035 , S2CID 119108982 .
^ "rho Hya" . SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2017-01-08 .{{cite web }}
: CS1 maint: postscript (link )
^ 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 , S2CID 14878976 .
^ Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal , 122 (6): 3466–3471, Bibcode :2001AJ....122.3466M , doi :10.1086/323920 .
^ Burnham, Robert (2013), Burnham's Celestial Handbook , An Observer's Guide to the Universe Beyond the Solar System, vol. 2, Courier Corporation, p. 1014, ISBN 978-0486317939 .
^ 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
^ 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
^ (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 28 日 Archived 2011-05-22 at the Wayback Machine
^ 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