21 Canum Venaticorum

21 Canum Venaticorum is a single[9] variable star[5] in the northern constellation of Canes Venatici, located 277 light years away from the Sun.[1] This object has the variable star designation BK Canum Venaticorum; 21 Canum Venaticorum is the Flamsteed designation. It is visible to the naked eye as a faint white-hued star with a baseline apparent visual magnitude of +5.14.[2]

21 Canum Venaticorum
Observation data
Epoch J2000      Equinox J2000
Constellation Canes Venatici
Right ascension 13h 18m 14.50967s[1]
Declination +49° 40′ 55.4245″[1]
Apparent magnitude (V) +5.14[2]
Characteristics
Spectral type B9 IV (Si)[3] or A0 V Si:[4]
B−V color index −0.049±0.002[2]
Variable type α2 CVn[5]
Astrometry
Radial velocity (Rv)−2.9±2.8[2] km/s
Proper motion (μ) RA: −35.235[1] mas/yr
Dec.: +16.655[1] mas/yr
Parallax (π)11.7559 ± 0.1344[1] mas
Distance277 ± 3 ly
(85.1 ± 1.0 pc)
Absolute magnitude (MV)0.48[6]
Details
Mass2.73[7] M☉
Radius2.8±0.3[6] R☉
Luminosity72.49[2] L☉
Surface gravity (log g)4.05[7] cgs
Temperature11,036±375[7] K
Rotational velocity (v sin i)96[7] km/s
Age201[7] Myr
Other designations
21 CVn, BK Canum Venaticorum, BD+50° 1994, FK5 3063, HD 115735, HIP 64906, HR 5023, SAO 44556[8]
Database references
SIMBADdata

According to Garrison et al. (1994)[3] this is a B-type subgiant star with a stellar classification of B9 IV (Si), where the suffix notation indicates this is a Silicon star. Cowley et al. (1969) listed it with a class of A0 V Si:,[4] which would match an A-type main-sequence star with the ':' indicating some uncertainty in the classification. It is a marginally chemically-peculiar star[10] with weaker than normal helium absorption lines and displaying helium line variability.[11] The widths of the lines of ionized silicon vary with a period of 21.12 ± 0.48 hours.[12]

21 Canum Venaticorum is classified as an Alpha2 Canum Venaticorum type variable star and its brightness varies by 0.04 magnitudes over a period of 18.4 hours.[5] It is around 201 million years old and is spinning with a relatively high projected rotational velocity of 96 km/s.[7] The star has 2.73[7] times the mass of the Sun and 2.8[6] times the Sun's radius. It is radiating 72[2] times the luminosity of the Sun from its photosphere at an effective temperature of 11,036 K.[7]

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. Garrison, R. F; Gray, R. O (1994), "The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation", The Astronomical Journal, 107: 1556, Bibcode:1994AJ....107.1556G, doi:10.1086/116967.
  4. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
  5. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869, retrieved 2019-01-27.
  6. North, P. (June 1998), "Do SI stars undergo any rotational braking?", Astronomy and Astrophysics, 334: 181–187, arXiv:astro-ph/9802286, Bibcode:1998A&A...334..181N
  7. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  8. "21 CVn". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-07-27.
  9. Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  10. Zverko, J.; et al. (March 1994), "Abundance Determination in the Chemically Peculiar Cp-Star 21-CANUM-VENATICORUM by Means of Spectrum Synthesis", Astronomy and Astrophysics, 283 (3): 932, Bibcode:1994A&A...283..932Z.
  11. Zverko, J. (September 1984), "Classification of Ap-Stars HR 830 and 21 CVn", Bulletin of the Astronomical Institute of Czechoslovakia, 35: 294, Bibcode:1984BAICz..35..294Z.
  12. Sriraghavan, S. M.; Jayakumar, K.; Babu, G. S. D.; Sajutha, S. (June 2004), "Variation of the Si II features in the chemically peculiar star - HD 115735", Bulletin of the Astronomical Society of India, 32 (2): 113, Bibcode:2004BASI...32..113S.
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