Alpha Comae Berenices

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.

α Comae Berenices

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
(combined)[2]
A: 4.85 / B: 5.53[3]
Characteristics
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]
Astrometry
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
Distance58.1 ± 0.9 ly
(17.8 ± 0.3 pc)
Absolute magnitude (MV)3.82[7]
Orbit[8]
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)
(secondary)		100.563±0.026°
Details
A
Mass1.237[9] M☉
Luminosity1.72[10] L☉
Surface gravity (log g)4.19[11] cgs
Temperature6,365[11] K
Metallicity [Fe/H]−0.23[11] dex
B
Mass1.087[9] M☉
Luminosity1.75[10] L☉
Temperature6,378[10] K
Other designations
α Com, Alpha Comae Berenices, Alpha Com, 42 Comae Berenices, 42 Com, STF 1728, ADS 8804 , BD+18 2697, CCDM J13100+1732, GC 17833, Gliese 501, HIP 64241, IDS 13051+1803 AB, LTT 13802, NLTT 33105, PPM 129630, SAO 100443, WDS 13100+1732.[6][12][13]
A: HD 114378, HR 4968
B: HD 114379, HR 4969
Database references
SIMBADdata

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.

Nomenclature

α Comae Berenices (Latinised to Alpha Comae Berenices) is the system's Bayer designation. The designations of the two components as Alpha Comae Berenices A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[15]

The system 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)[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]

Properties

Although Alpha Comae Berenices bears the title "alpha", at magnitude 4.32 it is actually fainter than Beta Comae Berenices.

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.

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References
  1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. 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 Archived 2005-04-24 at the Wayback Machine, United States Naval Observatory. Accessed on line September 3, 2008.
  4. Diadem Archived 2008-05-11 at the Wayback Machine, Jim Kaler, Stars. Accessed on line September 3, 2008.
  5. 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. 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/0509399, Bibcode:2006A&A...446..267R, doi:10.1051/0004-6361:20053911.
  8. 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:1501.05639. Bibcode:2015AJ....150..140M. doi:10.1088/0004-6256/150/5/140.
  9. Pavlovic, R.; Todorovic, N. (2005). "Orbits of Seven Edge-On Visual Double Stars". Serbian Astronomical Journal. 170: 73. Bibcode:2005SerAJ.170...73P.
  10. Ten Brummelaar, Theo; Mason, Brian D.; McAlister, Harold A.; Roberts, Lewis C.; Turner, Nils H.; Hartkopf, William I.; Bagnuolo, William G. (2000). "Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory". The Astronomical Journal. 119 (5): 2403. Bibcode:2000AJ....119.2403T. doi:10.1086/301338.
  11. Soubiran, Caroline; Le Campion, Jean-François; Brouillet, Nathalie; Chemin, Laurent (2016). "The PASTEL catalogue: 2016 version". Astronomy and Astrophysics. 591: A118. arXiv:1605.07384. Bibcode:2016A&A...591A.118S. doi:10.1051/0004-6361/201628497.
  12. HD 114378 -- Star in double system, database entry, SIMBAD, accessed on line September 3, 2008.
  13. HD 114379 -- Star in double system, database entry, SIMBAD, accessed on line September 3, 2008.
  14. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  15. 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].
  16. "International Astronomical Union | IAU". www.iau.org. Retrieved 2017-03-31.
  17. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  18. (in 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.
  19. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2009-09-29 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  20. (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived 2008-09-24 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  21. Richard Hinckley Allen: Star Names — Their Lore and Meaning: Coma Berenices
  22. Entry 13100+1732, discoverer code STF1728, components AB-C, The Washington Double Star Catalog Archived 2008-04-13 at the Wayback Machine, United States Naval Observatory. Accessed on line September 3, 2008.
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