Alpha Comae Berenices (α Comae Berenices, abbreviated Alpha Com, α Com) is a binary star in the constellation of Coma Berenices (Berenice's Hair), 17.8 parsecs (58 ly) away. It consists of two main sequence stars, each a little hotter and more luminous than the Sun.
Alpha Comae Berenices is said to represent the crown worn by Queen Berenice. The two components are designated Alpha Comae Berenices A (officially named Diadem/ˈdaɪədɛm/, the traditional name for the system)[14] and B.
The system bore the traditional names Diadem and Al Dafirah, the latter derived from the Arabic الضفيرة ađ̧-đ̧afīrah "the braid".[citation needed] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[17] It approved the name Diadem for the component Alpha Comae Berenices A on 1 February 2017 and it is now so included in the List of IAU-approved Star Names.[14]
In Chinese, 太微左垣 (Tài Wēi Zuǒ Yuán), meaning Left Wall of Supreme Palace Enclosure, refers to an asterism consisting of Alpha Comae Berenices, Eta Virginis, Gamma Virginis, Delta Virginis and Epsilon Virginis.[18] Consequently, the Chinese name for Alpha Comae Berenices itself is 太微左垣五 (Tài Wēi Zuǒ Yuán wǔ, English: the Fifth Star of Left Wall of Supreme Palace Enclosure.),[19] representing 東上將 (Dōngshǎngjiāng), meaning The First Eastern General.[20] 東上將 (Dōngshǎngjiāng), westernized into Shang Tseang, but that name was designated for "v Comae Berenices" by R.H. Allen and the meaning is "a Higher General".[21]
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 AU, 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°.[22]
Alpha Comae Berenicis forms an isosceles triangle with globular star clusters Messier 53 and NGC 5053. The apparent diameter of this triangle is a little more than one degree. The location of Alpha Comae Berenicis is westward (preceding) of both globular star clusters.
^ abHR 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.
^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
