HD 81799
Star and suspected binary system in the constellation Hydra
HD 81799 (G Hydrae ) is a suspected astrometric binary [ 8] star system in the equatorial constellation of Hydra . It is visible to the naked eye with an apparent visual magnitude of 4.69.[ 2] parallax shift of mas [ 1] light years . It is moving further away from the Earth with a heliocentric radial velocity of 29 km/s.[ 1] proper motion , traversing the celestial sphere at the rate of ± 19 mas/yrposition angle of 136°.[ 9]
The stellar classification of the visible component is K2+ IIIb,[ 3] evolved K-type giant star . It is a red clump star, which indicates it is on the horizontal branch and is generating energy through helium fusion at its core .[ 4] interferometry -measured angular diameter of the primary, after correcting for limb darkening , is ± 0.03 mas [ 10] radius of the Sun .[ 6] [ 5] Sun's luminosity from its enlarged photosphere at an effective temperature of 4,490 K.[ 2]
The system is a likely (99.4% chance) source of the X-ray emission coming from these coordinates.[ 11]
References
^ a b c d e f g h Brown, A. G. A. ; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties" . Astronomy & Astrophysics 616 . A1. arXiv :1804.09365 Bibcode :2018A&A...616A...1G doi :10.1051/0004-6361/201833051 ^ a b c d e f Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (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 , S2CID 118362423 . ^ a b Keenan, P.; McNeil, R. (October 1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series , 71 : 245–266, Bibcode :1989ApJS...71..245K , doi :10.1086/191373 ^ a b Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal , 539 (2): 732–741, arXiv :astro-ph/0003329 Bibcode :2000ApJ...539..732A , doi :10.1086/309278 , S2CID 16673121 . ^ a b c 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 Lang, Kenneth R. (2006), Astrophysical formulae Birkhäuser , ISBN 3-540-29692-1 * ) is given by:
2
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10
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3
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50.3
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1.96
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AU
0.0046491
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21.2
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{\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(10^{-3}\cdot 50.3\cdot 1.96)\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 21.2\cdot R_{\bigodot }\end{aligned}}}
^ "HD 81799" . SIMBAD Centre de données astronomiques de Strasbourg . Retrieved 2018-07-24 .^ Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society , 389 (2): 869, arXiv :0806.2878 Bibcode :2008MNRAS.389..869E , doi :10.1111/j.1365-2966.2008.13596.x S2CID 14878976 . ^ Wroblewski, H.; Torres, C. (March 1998), "New proper motion determination of Luyten catalogue stars (LTT) with declination between -5° and -30° and right ascension between 0h and 13h 30m", Astronomy and Astrophysics Supplement , 128 : 457–458, Bibcode :1998A&AS..128..457W , doi :10.1051/aas:1998157 ^ Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics , 431 (2): 773–777, Bibcode :2005A&A...431..773R , doi :10.1051/0004-6361:20042039 ^ Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009), "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources", The Astrophysical Journal Supplement , 184 (1): 138–151, arXiv :0910.3229 Bibcode :2009ApJS..184..138H , doi :10.1088/0067-0049/184/1/138 , S2CID 119267456 .
