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12 Hydrae is a probable astrometric binary star system located 202 light years away from the Sun in the equatorial constellation of Hydra. It has the Bayer designation D Hydrae; 12 Hydrae is the Flamsteed designation. This system is visible to the naked eye as a faint, yellow-hued star with a combined apparent visual magnitude of 4.32. It is moving closer to the Earth with a heliocentric radial velocity of −8.5 km/s.

This was found to be a double star by R. A. Rossiter in 1953, with the magnitude 13.7 companion having an angular separation of 26.8″ along a position angle of 266°, as of 2016. The brighter, magnitude 4.32 component A is a spectroscopic binary. As of 2009, the orbital solution for this pair is of low quality, giving a period of roughly 4 years and an eccentricity of around 0.4.

The primary component is an aging giant star with a stellar classification of G8 IIIb CN-1, where the suffix notation indicates an underabundance of the cyanogen molecule. It is 910 million years old with 2.32 times the mass of the Sun. After exhausting the hydrogen at its core and evolving off the main sequence, the star has swollen to 11.5 times the Sun's radius. It is radiating 77 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,968 K.

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. ^ 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.
3. ^ Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373
4. ^ Ammler-von Eiff, Matthias; Reiners, Ansgar (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
5. ^ Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, archived from the original on 2017-08-01, retrieved 2017-06-02.
6. ^ Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", Astronomical Journal, 150 (3), 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114.
7. ^ "12 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 1, 2019.
8. 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.
9. Rossiter, R. A. (February 1953), "Seventh list of new Southern double stars found at the Lamont-Hussey Observatory of the University of Michigan at Bloemfontein, South Africa.", Astronomical Journal, 58: 29–30, Bibcode:1953AJ.....58...29R, doi:10.1086/106804.

• Hydra (constellation)
• G-type giants
• Flamsteed objects
• Bayer objects
• Bright Star Catalogue objects
• Henry Draper Catalogue objects
• Hipparcos objects
• Durchmusterung objects
• Double stars
• Spectroscopic binaries