Cor Caroli

Cor Caroli seen from northern England on March 1, 2011.

Cor Caroli (α CVn, α Canum Venaticorum, Alpha Canum Venaticorum) is the brightest star in the northern constellation Canes Venatici. It is a binary star consisting of two distantly separated components. The name Cor Caroli means "Charles's Heart", and was named in the 17th century to honour the King Charles I of England who was beheaded in 1649.

Names

In the western world the star had no name until the 17th century, when it was named Cor Caroli, which means "Charles's Heart". There has been some uncertainty whether it was named in honour of King Charles I of England, who was executed in 1649 during the English Civil War, or to his son, Charles II, who restored the English monarchy to the throne in 1660. The name was coined in 1660 by Sir Charles Scarborough, physician to Charles II, who claimed the star seemed to shine exceptionally brightly on the night of Charles II's return to England. In Star Names, R.H. Allen claimed that Scarborough suggested the name to Edmund Halley and intended it to refer to Charles II.^[1] However, Robert Burnham Jr. notes that "the attribution of the name to Halley appears in a report published by J. E. Bode at Berlin in 1801, but seems to have no other verification".^[2] In Star Tales, Ian Ridpath points out that the name's first appearance on a star map was in the 1673 chart of Francis Lamb, who labelled it Cor Caroli Regis Martyris ("the heart of Charles the martyred king"), clearly indicating that it was seen as referring to Charles I.^[3]

In Chinese, 常陳 (Cháng Chén), meaning Imperial Guards, refers to an asterism consisting of α Canum Venaticorum, 10 Canum Venaticorum, β Canum Venaticorum, 6 Canum Venaticorum, 2 Canum Venaticorum, 67 Ursae Majoris.^[4] Consequently, α Canum Venaticorum itself is known as 常陳一 (Cháng Chén yī, English: the First Star of Imperial Guards.)^[5] From this Chinese name, the name Chang Chen was appeared.^[6]

Characteristics

Cor Caroli is a binary star with a combined apparent magnitude of 2.81. The two stars are 19.6 arcseconds apart in the sky and are easily resolved in small telescopes. The system lies approximately 110 light years from Earth. The brighter of the two stars is designated α² Canum Venaticorum, the fainter α¹ Canum Venaticorum.^[7]

Cor Caroli marks the northern vertex of the Diamond of Virgo asterism.

α² Canum Venaticorum

α² Canum Venaticorum

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Canes Venatici
Right ascension	12^h 56^m 01.6674^s[8]
Declination	+38° 19′ 06.167″[8]
Apparent magnitude (V)	2.84 to 2.98[9]
Characteristics
Spectral type	A0pSiEuHg[10]
U−B color index	−0.32[10]
B−V color index	−0.12[10]
V−R color index	0.0[8]
R−I color index	−0.06[10]
Variable type	ACV[9]
Astrometry
Radial velocity (Rv)	−3.3 ± 2[8] km/s
Proper motion (μ)	RA: −233.43[8] mas/yr Dec.: 54.98[8] mas/yr
Parallax (π)	29.60 ± 1.04[8] mas
Distance	110 ± 4 ly (34 ± 1 pc)
Absolute magnitude (MV)	0.3[11]
Details
Radius	4.10[12] R☉
Rotational velocity (v sin i)	29[10] km/s
Other designations
α Canum Venaticorum A, α CVn A, Alpha Canum Venaticorum A, Alpha CVn A, α^2 CVn, Alpha^2 Canum Venaticorum, Alpha^2 CVn, 12 Canum Venaticorum A, 12 CVn A, ADS 8706 A, BD+39 2580A, CCDM J12560+3819A, FK5 485, GC 17557, HD 112413, HIP 63125, HR 4915, IDS 12514+3851 A, LTT 13717, NLTT 32338, PPM 76815, SAO 63257.[8][10]
Database references
SIMBAD	data

α² Canum Venaticorum has spectral type A0, and has an apparent visual magnitude which varies between 2.84 and 2.98, with a period of 5.47 days.^[8][9] It is a chemically peculiar star with a strong magnetic field, about 5,000 times as strong as the Earth's, and is also classified as an Ap/Bp star.^[13] Its atmosphere has overabundances of some elements, such as silicon, mercury, and europium. This is thought to be due to some elements sinking down into the star under the force of gravity while others are elevated by radiation pressure.^[7][13] This star is the prototype of a class of variable stars, the so-called α² Canum Venaticorum stars. The strong magnetic field of these stars is believed to produce starspots of enormous extent. Due to these starspots the brightness of α² Canum Venaticorum stars varies considerably during their rotation.

α¹ Canum Venaticorum

α¹ Canum Venaticorum

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Canes Venatici
Right ascension	12^h 56^m 00.4522^s[14]
Declination	+38° 18′ 53.685″[14]
Apparent magnitude (V)	5.60[14]
Characteristics
Spectral type	F0V[14]
U−B color index	−0.03[15]
B−V color index	+0.34[15]
V−R color index	0.3[14]
R−I color index	+0.23[15]
Astrometry
Radial velocity (Rv)	−3.1 ± 2[14] km/s
Proper motion (μ)	RA: −203.89[14] mas/yr Dec.: 88.34[14] mas/yr
Parallax (π)	29.60 ± 1.04[16] mas
Distance	110 ± 4 ly (34 ± 1 pc)
Absolute magnitude (MV)	4[11]
Details
Radius	1.29[17] R☉
Rotational velocity (v sin i)	8[15] km/s
Other designations
α^1 CVn, Alpha^1 Canum Venaticorum, Alpha^1 CVn, α Canum Venaticorum B, α CVn B, Alpha Canum Venaticorum B, Alpha CVn B, 12 Canum Venaticorum B, 12 CVn B, ADS 8706 B, BD+39 2580B, BD+39 2580, CCDM J12560+3819B, GC 17556, HD 112412, HIP 63121, HR 4914, IDS 12514+3851 B, LTT 13718, NLTT 32336, PPM 76814, SAO 63256.[14][15]
Database references
SIMBAD	data

α¹ Canum Venaticorum is a F-type main sequence star. It is considerably fainter than its companion and has an apparent visual magnitude of approximately 5.60.^[14]

Namesakes

USS Cor Caroli (AK-91) was a United States Navy Crater class cargo ship named after the star.

References

1. R.H. Allen, Star Names: Their Lore and Meaning.
2. Robert Burnham, Jr. Burnham's Celestial Handbook, Volume 1, p. 359.
3. Ian Ridpath: "Star Tales", Canes Venatici. See also Deborah J. Warner, The Sky Explored: Celestial Cartography 1500-1800.
4. (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
5. (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
6. Richard Hinckley Allen: Star Names — Their Lore and Meaning: Canes Venatici
7. Cor Caroli, Stars, Jim Kaler. Accessed on line September 15, 2008.
8. V* alf02 CVn -- Variable Star of alpha2 CVn type, database entry, SIMBAD. Accessed on line November 2, 2009.
9. alf 2 CVn, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line November 2, 2009.
10. HR 4915, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 2, 2009.
11. From apparent magnitude and parallax.
12. HD 112413, database entry, Catalog of Apparent Diameters and Absolute Radii of Stars (CADARS), 3rd edition, L. E. Pasinetti-Fracassini, L. Pastori, S. Covino, and A. Pozzi, CDS ID II/224. Accessed on line November 2, 2009.
13. "Cor Caroli", p. 49, The hundred greatest stars, James B. Kaler, Springer, 2002, ISBN 0-387-95436-8.
14. LTT 13718 -- High proper-motion Star, database entry, SIMBAD. Accessed on line November 2, 2009.
15. HR 4914, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line November 2, 2009.
16. NLTT 32336, database entry, New HIP-based parallaxes for 424 faint stars, A. Gould and J. Chanamé, CDS ID J/ApJS/150/455. Accessed on line November 2, 2009. Also see New Hipparcos-based Parallaxes for 424 Faint Stars, Andrew Gould and Julio Chanamé, The Astrophysical Journal Supplement Series 150, #2 (February 2004), pp. 455–464, doi:10.1086/381147, Bibcode: 2004ApJS..150..455G.
17. HD 112412, database entry, Catalog of Apparent Diameters and Absolute Radii of Stars (CADARS), 3rd edition, L. E. Pasinetti-Fracassini, L. Pastori, S. Covino, and A. Pozzi, CDS ID II/224. Accessed on line November 2, 2009.