Alpha Comae Berenices
Coma Berenices constellation
Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||13h 09m 59.2766s|
|Declination||+17° 31′ 45.953″|
|Apparent magnitude (V)||4.29 to 4.35
A: 4.85 / B: 5.53
|Spectral type||A: F5V / B: F5V
|U−B color index||−0.06|
|B−V color index||0.45|
|V−R color index||0.2|
|R−I color index||0.2|
|Radial velocity (Rv)||−17.7 ± 0.9 km/s|
|Proper motion (μ)||RA: −445.96 mas/yr
Dec.: 129.69 mas/yr
|Parallax (π)||51.7 ± 5.7 mas|
|Distance||approx. 63 ly
(approx. 19 pc)
|Absolute magnitude (MV)||3 (combined)|
|Period (P)||26.052 ± 0.013 years|
|Semi-major axis (a)||0.67633 ± 0.00095″|
|Eccentricity (e)||0.5083 ± 0.0026|
|Inclination (i)||90.098 ± 0.051°|
|Longitude of the node (Ω)||192.235 ± 0.047°|
|Periastron epoch (T)||B1989.2052 ± 0.0061|
|Argument of periastron (ω)
|280.121 ± 0.070°|
Alpha Comae Berenices (Alpha Com, α Com, α Comae Berenices) is a star in the constellation Coma Berenices (Berenice's Hair). Although it has the Bayer designation "alpha", at magnitude 4.32 it is actually fainter than Beta Comae Berenices. It has the traditional name Diadem. It is said to represent the crown worn by Queen Berenice. A name occasionally seen is Al Dafirah, from the Arabic الضفيرة ađ̧-đ̧afīrah "the braid".
In Chinese, 太微左垣 (Tài Wēi Zuǒ Yuán), meaning Left Wall of Supreme Palace Enclosure, refers to an asterism consisting of α Comae Berenices, η Virginis, γ Virginis, δ Virginis and ε Virginis. Consequently, α Comae Berenices itself is known as 太微左垣五 (Tài Wēi Zuǒ Yuán wǔ, English: the Fifth Star of Left Wall of Supreme Palace Enclosure.), representing 東上將 (Dōngshǎngjiāng), meaning The First Eastern General. 東上將 (Dōngshǎngjiāng), westernized into Shang Tseang, but the name Shang Tseang was designated for "v Comae Berenices" by R.H. Allen and the meaning is "a Higher General" 
It is a binary star, with almost equal components of magnitudes 5.05m and 5.08m orbiting each other with a period of 25.87 years. The system, estimated to be 65 light years distant, appears so nearly "edge-on" from the Earth that the two stars appear to move back-and-forth in a straight line with a maximum separation of only 0.7 arcsec. It is not known whether eclipses occur between the two components at periastron (minimum separation)—the only such passage since the determination of the orbit, in 1990, was not quantitatively followed by observers.
- NSV 6116 -- Variable Star, database entry, SIMBAD. Accessed on line September 3, 2008.
- NSV 6116, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line September 3, 2008.
- Entry 13100+1732, Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory. Accessed on line September 3, 2008.
- Diadem, Jim Kaler, Stars. Accessed on line September 3, 2008.
- HR 4968, 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 September 3, 2008.
- GJ 501, database entry, Preliminary Version of the Third Catalogue of Nearby Stars, W. Gliese and H. Jahreiss, CDS ID V/70A. Accessed on line September 3, 2008.
- From apparent magnitude and parallax.
- HD 114378 -- Star in double system, database entry, SIMBAD, accessed on line September 3, 2008.
- HD 114379 -- Star in double system, database entry, SIMBAD, accessed on line September 3, 2008.
- (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.
- (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.
- (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
- Richard Hinckley Allen: Star Names — Their Lore and Meaning: Coma Berenices
- Entry 13100+1732, discoverer code STF1728, components AB-C, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line September 3, 2008.