Astronomy:HD 81799
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 27m 18.43258s[1] |
| Declination | −22° 20′ 37.4967″[1] |
| Apparent magnitude (V) | 4.69[2] |
| Characteristics | |
| Spectral type | K2+ IIIb[3] |
| B−V color index | 1.154[4] |
| Astrometry | |
| Radial velocity (Rv) | 29.05±0.28[1] km/s |
| Proper motion (μ) | RA: +160.160[1] mas/yr Dec.: −173.131[1] mas/yr |
| Parallax (π) | 19.8887 ± 0.3128[1] mas |
| Distance | 164 ± 3 ly (50.3 ± 0.8 pc) |
| Absolute magnitude (MV) | 1.32[5] |
| Details | |
| Radius | 10.6[6] R☉ |
| Luminosity | 41.97[5] L☉ |
| Surface gravity (log g) | 2.43[2] cgs |
| Temperature | 4,490[2] K |
| Metallicity [Fe/H] | −0.01[2] dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
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] The distance to this system, as determined from an annual parallax shift of 19.9 mas,[1] is 164 light years. It is moving further away from the Earth with a heliocentric radial velocity of 29 km/s.[1] The system has a relatively high rate of proper motion, traversing the celestial sphere at the rate of 233±19 mas/yr along a position angle of 136°.[9]
The stellar classification of the visible component is K2+ IIIb,[3] which matches an 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] The interferometry-measured angular diameter of the primary, after correcting for limb darkening, is 1.96±0.03 mas,[10] which, at its estimated distance, equates to a physical radius of about 10.6 times the radius of the Sun.[6] It is radiating 42[5] times the 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
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 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, doi:10.1051/0004-6361/201014247, Bibcode: 2010A&A...515A.111S.
- ↑ 3.0 3.1 Keenan, P.; McNeil, R. (October 1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series 71: 245–266, doi:10.1086/191373, Bibcode: 1989ApJS...71..245K
- ↑ 4.0 4.1 Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal 539 (2): 732–741, doi:10.1086/309278, Bibcode: 2000ApJ...539..732A.
- ↑ 5.0 5.1 5.2 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A.
- ↑ 6.0 6.1 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1, https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41. The radius (R*) is given by:
- [math]\displaystyle{ \begin{align} 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{align} }[/math]
- ↑ "HD 81799". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+81799.
- ↑ 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, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode: 2008MNRAS.389..869E.
- ↑ 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, doi:10.1051/aas:1998157, Bibcode: 1998A&AS..128..457W.
- ↑ Richichi, A. et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431 (2): 773–777, doi:10.1051/0004-6361:20042039, Bibcode: 2005A&A...431..773R
- ↑ 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, doi:10.1088/0067-0049/184/1/138, Bibcode: 2009ApJS..184..138H.
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