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HD 20644 is a suspected binary star system in the constellation Aries. It has an orange hue and is visible to the naked eye with an apparent visual magnitude of 4.47. The system is located at a distance of approximately 540 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −3 km/s.

The visible component is an aging giant star with a stellar classification of K3IIIa Ba0.5, where the suffix notation indicates this is a mild barium star. The atmosphere of this star is enriched with s-process elements that are posited to have been transferred from what is now a white dwarf companion when it evolved along the asymptotic giant branch (AGB). Alternatively, this star may itself be on the AGB.

HD 20644 is about 350 million years old with three times the mass of the Sun and is spinning with a projected rotational velocity of 1.4 km/s. With the supply of hydrogen at its core exhausted, it has expanded to 66 times the Sun's radius. It is radiating 1,576 times the luminosity of the Sun from its photosphere at an effective temperature of 4,485 K.

References

1. ^ 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.
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. ^ Baines, Ellyn K.; et al. (2018), "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer", The Astronomical Journal, 155 (1), 30, arXiv:1712.08109, Bibcode:2018AJ....155...30B, doi:10.3847/1538-3881/aa9d8b, S2CID 119427037.
5. ^ Lèbre, A.; et al. (May 2006), "Lithium abundances and rotational behavior for bright giant stars", Astronomy and Astrophysics, 450 (3): 1173–1179, Bibcode:2006A&A...450.1173L, doi:10.1051/0004-6361:20053485.
6. "HD 20644". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-12-22.
7. Yang, Guo-Chao; et al. (January 2016), "Chemical abundance analysis of 19 barium stars", Research in Astronomy and Astrophysics, 16 (1): 019, arXiv:1602.08704, Bibcode:2016RAA....16...19Y, doi:10.1088/1674-4527/16/1/019, S2CID 14474857, 19.
8. Mennessier, M. O.; et al. (October 1997), "Barium stars, galactic populations and evolution", Astronomy and Astrophysics, 326: 722–730, Bibcode:1997A&A...326..722M.

v t e Constellation of Aries
Aries in Chinese astronomy List of stars in Aries
Stars	Bayer α (Hamal) β (Sheratan) γ (Mesarthim) δ (Botein) ε ζ η θ ι κ λ μ ν ξ ο π ρ ρ ρ σ τ τ Flamsteed 1 4 7 10 11 14 15 16 19 20 21 23 26 27 29 30 31 33 35 36 38 39 (Lilii Borea) 40 41 (Bharani) 47 49 50 51 52 53 54 55 56 59 60 62 64 65 66 54 Cet 85 Cet Variable TZ UX VZ (16 Tri) HR 577 728 803 952 999 HD 12661 20367 Other BD+20°307 HIP 14810 HAT-P-25 Teegarden's Star WASP-11/HAT-P-10 WD 0145+234
Exoplanets α Arietis b HD 12661 b c HIP 14810 b c d Teegarden's Star b c WASP-11b/HAT-P-10b
Galaxies	NGC 677 680 691 694 695 716 765 770 772 781 803 817 820 821 871 877 900 901 903 904 918 935 938 972 990 992 1024 1134 1156 Other 1ES 0229+200 3C 79 4C +28.07 AO 0235+164 IC 167 IC 1801 PSO J0309+27 Segue 2 UGC 2140
Galaxy clusters MS 0302+17
Astronomical events GRB 060218
Category

• K-type giants
• Barium stars
• Aries (constellation)
• Durchmusterung objects
• Henry Draper Catalogue objects
• Hipparcos objects
• Bright Star Catalogue objects