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21 Canum Venaticorum is a single variable star in the northern constellation of Canes Venatici, located 277 light years away from the Sun. 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.

According to Garrison et al. (1994) 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:, which would match an A-type main-sequence star with the ':' indicating some uncertainty in the classification. It is a marginally chemically-peculiar star with weaker than normal helium absorption lines and displaying helium line variability. The widths of the lines of ionized silicon vary with a period of 21.12 ± 0.48 hours.

21 Canum Venaticorum is classified as an Alpha Canum Venaticorum type variable star and its brightness varies by 0.04 magnitudes over a period of 18.4 hours. Its variability was discovered in 1984 by Juraj Zverko and it was given its variable star designation in 1987. It is around 201 million years old and is spinning with a relatively high projected rotational velocity of 96 km/s. The star has 2.73 times the mass of the Sun and 2.8 times the Sun's radius. It is radiating 72 times the luminosity of the Sun from its photosphere at an effective temperature of 11,036 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. ^ 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.
13. Zverko, J. (September 1984). "Classification of Ap-Stars HR 830 and 21 CVn". Bulletin of the Astronomical Institute of Czechoslovakia. 35: 294–299. Bibcode:1984BAICz..35..294Z. Retrieved 28 August 2024.
14. Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Kireeva, N. N. (August 1987). "The 68th Name-List of Variable Stars". Information Bulletin on Variable Stars. 3058 (3058): 1. Bibcode:1987IBVS.3058....1K. Retrieved 28 August 2024.

v t e Constellation of Canes Venatici
Canes Venatici in Chinese astronomy Giant Void List of stars in Canes Venatici
Stars	Bayer α α (Cor Caroli) β (Chara) Flamsteed 4 5 6 10 19 20 21 24 25 Variable R Y (La Superba) RS AM AW BH DG HR 4997 Other Gliese 521 HAT-P-12 HAT-P-36 (Tuiren) CWISE J1249+3621
Exoplanets HAT-P-12b
Star clusters Messier 3
Galaxies	Messier 51 a (Whirlpool Galaxy) b 63 94 106 NGC 4111 4138 4145 4151 4163 4183 4214 4217 4242 4244 4395 4399 4400 4401 4449 4485 4490 4534 4618 4625 4627 4631 4656 4657 4707 4800 4861 5002 5003 5005 5023 5033 5112 5223 5229 5238 5273 5371 5394 Numbered I II Other 3C 285 3C 286 3C 288 B2 1308+326 DDO 169 IC 883 IC 4182 IC 4263 IC 4271 I Zwicky 36 KKR 03 4C +41.26 TON 618
Galaxy clusters Canes II Group M51 Group M94 Group NGC 4631 Group
Astronomical events GRB 090429B SN 1994I SN 2005cs SN 2008ax
Category

• B-type subgiants
• A-type main-sequence stars
• Ap stars
• Alpha2 Canum Venaticorum variables
• Canes Venatici
• Flamsteed objects
• Durchmusterung objects
• Henry Draper Catalogue objects
• Hipparcos objects
• Bright Star Catalogue objects
• Objects with variable star designations