26 Hydrae

26 Hydrae is a binary star[3] system located 334 light years away from the Sun in the equatorial constellation of Hydra. It is visible to the naked eye as a faint, yellow-hued point of light with a combined apparent visual magnitude of 4.77,[2] just a few degrees away from Alphard. The system is moving closer to the Earth with a leisurely radial velocity of -1 km/s.[8]

26 Hydrae
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension  09h 19m 46.38309s[1]
Declination −11° 58′ 29.4577″[1]
Apparent magnitude (V) 4.770[2] + 12.4[3]
Characteristics
Spectral type G7III[4] or G8II[5]
U−B color index +0.67[6]
B−V color index +0.927±0.017[7]
Astrometry
Radial velocity (Rv)−1.18±0.09[8] km/s
Proper motion (μ) RA: −29.269[1] mas/yr
Dec.: +11.613[1] mas/yr
Parallax (π)9.7770 ± 0.1610[1] mas
Distance334 ± 5 ly
(102 ± 2 pc)
Absolute magnitude (MV)−0.29[7]
Details
26 Hya A
Mass2.72[9] M☉
Radius15.14+0.81
−2.47[1] R☉
Luminosity138.5±2.7[1] L☉
Surface gravity (log g)2.48±0.07[10] cgs
Temperature5,003±82[9] K
Metallicity [Fe/H]−0.13±0.06[10] dex
Rotational velocity (v sin i)2.7[8] km/s
Age0.51[9] Gyr
Other designations
26 Hya, BD−11°2609, FK5 2741, HD 80499, HIP 45751, HR 3706, SAO 155096, WDS J09198-1158AB[11]
Database references
SIMBADdata

Keenan and McNeil (1989) gave the brighter component a stellar classification of G7 III,[4] matching an aging giant star. Houk and Swift (1999) have it classed as a G8II[5] bright giant. This is a red clump giant,[12] which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. It has a high lithium abundance and displays a far infrared emission excess.[13] The star is an estimated 510[9] million years old with 2.72[9] times the mass of the Sun and has expanded to 15[1] times the Sun's radius. It is radiating 139[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 5,003 K.[9]

The secondary component is a magnitude 12.4 star at an angular separation of 3.2″, as of 2008.[3]

References
  1. 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. Gaia DR2 record for this source at VizieR.
  2. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  3. 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.
  4. 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.
  5. Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
  6. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  7. 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.
  8. Massarotti, Alessandro; et al. (2008). "Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity". The Astronomical Journal. 135 (1): 209–231. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209.
  9. Luck, R. Earle (2015). "Abundances in the Local Region. I. G and K Giants". The Astronomical Journal. 150 (3): 88. arXiv:1507.01466. Bibcode:2015AJ....150...88L. doi:10.1088/0004-6256/150/3/88.
  10. Wu, Yue; et al. (2010). "Coudé-feed stellar spectral library – atmospheric parameters". Astronomy & Astrophysics. 525: A71. arXiv:1009.1491. Bibcode:2011A&A...525A..71W. doi:10.1051/0004-6361/201015014.
  11. "26 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-06-12.
  12. 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.
  13. Jasniewicz, G.; et al. (2000). da silva, L.; de Medeiros, R.; Spite, M (eds.). Search for Lithium-Rich Stars Among G-K Giants with IR-excess. The Light Elements and their Evolution, Proceedings of IAU Symposium 198, held 22-26 Nov 1999, Natal, Brazil. p. 325. Bibcode:2000IAUS..198..325J.
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