Alpha Comae Berenices

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α Comae Berenices
Coma Berenices constellation map.png
Coma Berenices constellation
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Coma Berenices
Right ascension 13h 09m 59.285s[1]
Declination +17° 31′ 46.04″[1]
Apparent magnitude (V) 4.29 to 4.35
A: 4.85 / B: 5.53[3]
Spectral type A: F5V / B: F5V
(binary star)[4]
U−B color index −0.06[5]
B−V color index 0.45[5]
V−R color index 0.2[6]
R−I color index 0.2[6]
Radial velocity (Rv) −17.7±0.9[6] km/s
Proper motion (μ) RA: −433.13±0.70[1] mas/yr
Dec.: 141.24±0.51[1] mas/yr
Parallax (π) 56.10 ± 0.89[1] mas
Distance 58.1 ± 0.9 ly
(17.8 ± 0.3 pc)
Absolute magnitude (MV) 3.82[7]
Period (P) 25.8696±0.008219 yr
Semi-major axis (a) 0.67144±0.00033"
Eccentricity (e) 0.51060±0.00061
Inclination (i) 90.0501±0.0062°
Longitude of the node (Ω) 12.2272±0.0098°
Periastron epoch (T) 57056.84±0.36
Argument of periastron (ω)
Other designations
α Com, Alpha Comae Berenices, Alpha Com, 42 Comae Berenices, 42 Com, STF 1728AB, ADS 8804 AB, BD+18°2697, CCDM J13100+1732AB, GC 17833, Gliese 501AB, HD 114378/114379, HIP 64241, HR 4968/4969, IDS 13051+1803 AB, LTT 13802, NLTT 33105, PPM 129630, SAO 100443, WDS 13100+1732AB.[6][9][10]
Database references

Alpha Comae Berenices (Alpha Com, α Com, α Comae Berenices), also named Diadem[11], 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 is said to represent the crown worn by Queen Berenice.


 α Comae Berenices (Latinised to Alpha Comae Berenices) is the star's Bayer designation.

It bore the traditional names Diadem and Al Dafirah, the latter derived from the Arabic الضفيرة ađ̧-đ̧afīrah "the braid".  In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalogue and standardize proper names for stars. The WGSN approved the name Diadem for this star on February 1st, 2017 and it is now so entered in the IAU Catalog of Star Names.[11]

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.[13] 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.),[14] representing 東上將 (Dōngshǎngjiāng), meaning The First Eastern General.[15] 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" [16]


It is a binary star, with almost equal components of magnitudes 5.05 m and 5.08 m orbiting each other with a period of 25.87 years. The system, estimated to be 58 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. Eclipses are predicted to occur between the two components however they have not been successfully observed due to miscalculations of the time of eclipse.[8]

The mean separation between them is approximately 10 A.U., about the distance between the Sun and Saturn.

The binary star has a visual companion, CCDM J13100+1732C, of apparent magnitude 10.2, located 89 arcseconds away along a position angle of 345°.[17]


  1. ^ a b c d e van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.  Vizier catalog entry
  2. ^ NSV 6116, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line September 3, 2008.
  3. ^ Entry 13100+1732, Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory. Accessed on line September 3, 2008.
  4. ^ Diadem, Jim Kaler, Stars. Accessed on line September 3, 2008.
  5. ^ a b 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.
  6. ^ a b c d NSV 6116 -- Variable Star, database entry, SIMBAD. Accessed on line September 3, 2008.
  7. ^ Reiners, A. (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation", Astronomy and Astrophysics, 446 (1): 267–277, arXiv:astro-ph/0509399Freely accessible, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911. 
  8. ^ a b Muterspaugh, Matthew W.; et al. (2015). "Predicting the α Comae Berenices Time of Eclipse: How 3 Ambiguous Measurements out of 609 Caused a 26 Year Binary's Eclipse to be Missed". The Astronomical Journal. 150 (5). 140. arXiv:1501.05639Freely accessible. Bibcode:2015AJ....150..140M. doi:10.1088/0004-6256/150/5/140. 
  9. ^ HD 114378 -- Star in double system, database entry, SIMBAD, accessed on line September 3, 2008.
  10. ^ HD 114379 -- Star in double system, database entry, SIMBAD, accessed on line September 3, 2008.
  11. ^ a b "IAU-CSN". 
  12. ^ "International Astronomical Union | IAU". Retrieved 2017-03-31. 
  13. ^ (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.
  14. ^ (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.
  15. ^ (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
  16. ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Coma Berenices
  17. ^ Entry 13100+1732, discoverer code STF1728, components AB-C, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line September 3, 2008.

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