HD 20644

HD 20644 is a suspected binary star[6] 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.[2] The system is located at a distance of approximately 540 light years from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −3 km/s.[2]

HD 20644
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Aries
Right ascension  03h 20m 20.36111s[1]
Declination +29° 02′ 54.4451″[1]
Apparent magnitude (V) 4.47[2]
Characteristics
Spectral type K3IIIa Ba0.5[3]
B−V color index 1.555±0.020[2]
Astrometry
Radial velocity (Rv)−3.09±0.28[2] km/s
Proper motion (μ) RA: −7.71[1] mas/yr
Dec.: −16.91[1] mas/yr
Parallax (π)6.01 ± 0.25[1] mas
Distance540 ± 20 ly
(166 ± 7 pc)
Absolute magnitude (MV)−1.63[2]
Details
Mass3.07±0.39[4] M☉
Radius75.32+3.30
−7.57[5] R☉
Luminosity1,292±89[5] L☉
Surface gravity (log g)2.00[4] cgs
Temperature3,987+217
−85[5] K
Metallicity [Fe/H]−0.27±0.04[2] dex
Rotational velocity (v sin i)1.4[6] km/s
Age350±140[4] Myr
Other designations
BD+28°516, FK5 2234, HD 20644, HIP 15549, HR 999, SAO 75871[7]
Database references
SIMBADdata

The visible component is an aging giant star with a stellar classification of K3IIIa Ba0.5,[3] 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).[8] Alternatively, this star may itself be on the AGB.[9]

HD 20644 is about 350[4] million years old with three[4] times the mass of the Sun and is spinning with a projected rotational velocity of 1.4 km/s.[6] With the supply of hydrogen at its core exhausted, it has expanded to 75[5] times the Sun's radius. It is radiating 1,292[5] times the luminosity of the Sun from its photosphere at an effective temperature of 3,987 K.[5]

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.
  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.
  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, 30, arXiv:1712.08109, Bibcode:2018AJ....155...30B, doi:10.3847/1538-3881/aa9d8b.
  5. 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.
  6. 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.
  7. "HD 20644". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-12-22.
  8. Yang, Guo-Chao; et al. (January 2016), "Chemical abundance analysis of 19 barium stars", Research in Astronomy and Astrophysics, 16 (1), arXiv:1602.08704, Bibcode:2016RAA....16...19Y, doi:10.1088/1674-4527/16/1/019, 19.
  9. Mennessier, M. O.; et al. (October 1997), "Barium stars, galactic populations and evolution", Astronomy and Astrophysics, 326: 722–730, Bibcode:1997A&A...326..722M.
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