}}{{Starbox reference
| Simbad = 21+CVn
}}{{Starbox end}}21 Canum Venaticorum is a single[21] variable star[7] 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.[3]According to Garrison et al. (1994)[4] this is a B-type subgiant star with a stellar classification of {{nowrap|B9 IV (Si)}}, where the suffix notation indicates this is a Silicon star. Cowley et al. (1969) listed it with a class of {{nowrap|A0 V Si:}},[5] which would match an A-type main-sequence star with the ':' indicating some uncertainty in the classification. It is a marginally chemically-peculiar star[27] with weaker than normal helium absorption lines and displaying helium line variability.[28] The widths of the lines of ionized silicon vary with a period of {{Convert|0.88|±|0.02|days|hours|disp=out|abbr=off}}.[29]
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 {{Convert|0.767|days|hours|disp=out|abbr=off}}.[7] It is around 201 million years old and is spinning with a relatively high projected rotational velocity of 96 km/s.[13] The star has 2.73[13] times the mass of the Sun and 2.8[12] times the Sun's radius. It is radiating 72[3] times the luminosity of the Sun from its photosphere at an effective temperature of 11,036 K.[13]
References
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6. ^1 {{citation | title=Abundance Determination in the Chemically Peculiar Cp-Star 21-CANUM-VENATICORUM by Means of Spectrum Synthesis | display-authors=1 | last1=Zverko | first1=J. | last2=Zboril | first2=M. | last3=Ziznovsky | first3=J. | journal=Astronomy and Astrophysics | volume=283 | issue=3 | page=932 | date=March 1994 | bibcode=1994A&A...283..932Z | postscript=. }}
7. ^1 2 3 4 5 6 7 8 {{citation | last1=David | first1=Trevor J. | last2=Hillenbrand | first2=Lynne A. | title=The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets | journal=The Astrophysical Journal | postscript=. | volume=804 | issue=2 | pages=146 | year=2015 | bibcode=2015ApJ...804..146D | arxiv=1501.03154 | doi=10.1088/0004-637X/804/2/146 }}
8. ^1 2 {{citation | last1=Garrison | first1=R. F | last2=Gray | first2=R. O | title=The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation | journal=The Astronomical Journal | postscript=. | volume=107 | pages=1556 | year=1994 | bibcode=1994AJ....107.1556G | doi=10.1086/116967 }}
9. ^1 2 3 {{citation | last1=North | first1=P. | title=Do SI stars undergo any rotational braking? | journal=Astronomy and Astrophysics | volume=334 | pages=181–187 | date=June 1998 | bibcode=1998A&A...334..181N | arxiv=astro-ph/9802286 }}
10. ^1 2 3 {{citation | display-authors=1 | last1=Samus | first1=N. N. | last2=Kazarovets | first2=E. V. | last3=Durlevich | first3=O. V. | last4=Kireeva | first4=N. N. | last5=Pastukhova | first5=E. N. | title=General Catalogue of Variable Stars | version=5.1 | journal=Astronomy Reports | year=2017 | volume=61 | issue=1 | pages=80–88 | url=http://www.sai.msu.su/gcvs/gcvs/ | accessdate=2019-01-27 | bibcode=2017ARep...61...80S | postscript=. }}
11. ^1 2 {{citation | display-authors=1 | last1=Cowley | first1=A. | last2=Cowley | first2=C. | last3=Jaschek | first3=M. | last4=Jaschek | first4=C. | title=A study of the bright A stars. I. A catalogue of spectral classifications | journal=Astronomical Journal | postscript=. | volume=74 | pages=375–406 | date=April 1969 | doi=10.1086/110819 | bibcode=1969AJ.....74..375C }}