Alpha Coronae Borealis

Alpha Coronae Borealis (α Coronae Borealis, abbreviated Alpha CrB, α CrB), officially named Alphecca /ælˈfɛkə/,[8] is an eclipsing binary star in the constellation of Corona Borealis. It is located about 75 light years from the Sun and contains two main sequence stars, one class A and one class G.

Alpha Coronae Borealis
Location of α Coronae Borealis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
Right ascension 15h 34m 41.268s[1]
Declination +26° 42′ 52.89″[1]
Apparent magnitude (V) 2.23[2] (2.21 - 2.32)[3]
Characteristics
Spectral type A0V/G5V[4]
U−B color index –0.03[2]
B−V color index –0.02[2]
Variable type Eclipsing binary[3]
Astrometry
Radial velocity (Rv)+1.7[5] km/s
Proper motion (μ) RA: 120.27 ± 0.19[1] mas/yr
Dec.: -89.58 ± 0.20[1] mas/yr
Parallax (π)43.46 ± 0.28[1] mas
Distance75.0 ± 0.5 ly
(23.0 ± 0.1 pc)
Absolute magnitude (MV)+0.16/+5.05[4]
Orbit[6]
Period (P)17.3599 d
Semi-major axis (a)0.2 AU
(2.981 × 1012 cm)
Eccentricity (e)0.370
Inclination (i)88.2 ± 0.1°
Argument of periastron (ω)
(primary)		311°
Details
α CrB A
Mass2.58[4] M☉
Radius2.89–3.04[4][6] R☉
Luminosity74[4] L☉
Surface gravity (log g)3.89[4] cgs
Temperature9,700[4] K
Rotational velocity (v sin i)139[7] km/s
Age0.314 Gyr
α CrB B
Mass0.92[4] M☉
Radius0.90[4][6] R☉
Luminosity0.81[4] L☉
Surface gravity (log g)4.50[4] cgs
Temperature5,800[4] K
Rotational velocity (v sin i)< 14[6] km/s
Other designations
Gemma, Alphekka, Alphecca, Gnosia, Ashtaroth, The Jewel, Gnosia Stella Coronae, 5 CrB, BD +27°2512, GCTP 3519.00, FK5 578, HD 139006, HIP 76267, HR 5793, SAO 83893.
Database references
SIMBADdata

Properties
α Coronae Borealis is the brightest star in the constellation Corona Borealis

Alpha Coronae Borealis is a binary system, its stars orbiting each other in an eccentric orbit every 17.36 days. Because the plane of this orbit is inclined at an angle of 88.2° to the line of sight to the Earth,[6] the pair form a detached eclipsing binary system similar to Algol (β Per). The periodic eclipses result in a magnitude variation of +2.21 to +2.32, which is hardly noticeable to the unaided eye.

The primary component is a white main sequence star that has a stellar classification of A0V and 2.6 times the mass of the Sun. Estimates of the star's radius range from 2.89 to 3.04 times the radius of the Sun.[4][6] An excess of infrared radiation at 24 μm and 70 μm has been detected about the primary star by the IRAS.[9] This suggests the presence of a large disc of dust and material around Alphecca, prompting speculation of a planetary or proto-planetary system similar to that currently assumed around Vega. The disk extends out to a radius of around 60 astronomical units (AU).[10]

The secondary component is a yellow main sequence star with an estimated stellar class of G5, 0.92 times the Sun's mass and 0.90 times the Sun's radius. The X-ray luminosity of this star is 6 × 1028 erg s−1, which is 30 times greater than the peak activity level of the Sun. This higher activity level is expected for a young star of this class. The corona has a temperature of about 5 MK, which is much hotter than the Sun's corona. The upper limit of 14 km/s for the equatorial rotation velocity is equivalent to a rotation period of 3 days. More likely, the rotation period is 7–9 days.[4][6]

The space velocity components of this star system are U = +14.257, V = +0.915 and W = +3.147 km/s. α CrB is believed to be a member of the Ursa Major Moving Group of stars that have a common motion through space.[11]

Nomenclature
α Coronae Borealis in optical light

α Coronae Borealis (Latinised to Alpha Coronae Borealis) is the star's Bayer designation.

It bore the traditional names Alphecca (or Alphekka), Gemma, Gnosia (Gnosia Stella Coronae), and Asteroth (or Ashtaroth). Alphecca is Arabic, short for نير الفكّة nayyir al-fakka "the bright (star) of the broken (ring of stars)". Gemma is Latin for "jewel". Gnosia is Greek (from γνωσία in hellenistic common and γνῶσις in ancient Greek, which means knowledge), short for Gnōsia stella corōnæ "star of the crown of Knossos".[12] Asteroth is Hebrew, עשתרות ‘ašterôt "Astarte (idols)" and mainly referred to the constellation.[12] As the brightest star in Corona Borealis, it lent its name to Alphekka Meridiana, the brightest in the constellation of Corona Australis. The International Astronomical Union Working Group on Star Names (WGSN) has chosen Alphecca as the preferred formal name for this star.[13]

The term nayyir al-fakka or Nir al Feccah appeared in the Al Achsasi Al Mouakket catalogue.[14]

In Chinese, 貫索 (Guàn Suǒ), meaning Coiled Thong, refers to an asterism consisting of Alpha Coronae Borealis, Pi Coronae Borealis, Theta Coronae Borealis, Beta Coronae Borealis, Gamma Coronae Borealis, Delta Coronae Borealis, Epsilon Coronae Borealis, Iota Coronae Borealis and Rho Coronae Borealis.[15] Consequently, the Chinese name for Alpha Coronae Borealis itself is 貫索四 (Guàn Suǒ sì, English: the Fourth Star of Coiled Thong.).[16]

See also

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. S2CID 18759600. Vizier catalog entry
  2. Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewskj, W. Z. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  3. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.
  4. Tomkin, J.; Popper, D. M. (June 1986). "Rediscussion of eclipsing binaries. XV - Alpha Coronae Borealis, a main-sequence system with components of types A and G". Astronomical Journal. 91: 1428. Bibcode:1986AJ.....91.1428T. doi:10.1086/114121.
  5. Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication: 0. Bibcode:1953GCRV..C......0W.
  6. Güdel, M.; Arzner, K.; Audard, M.; Mewe, R. (May 2003). "Tomography of a stellar X-ray corona: alpha Coronae Borealis". Astronomy and Astrophysics. 403: 155–171. Bibcode:2003A&A...403..155G. doi:10.1051/0004-6361:20030257.
  7. Royer, F.; Grenier, S.; Baylac, M.-O.; Gómez, A. E.; Zorec, J. (October 2002). "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i". Astronomy and Astrophysics. 393 (3): 897–911. arXiv:astro-ph/0205255. Bibcode:2002A&A...393..897R. doi:10.1051/0004-6361:20020943. S2CID 14070763. Table 8.
  8. "IAU Catalog of Star Names". Retrieved 28 July 2016.
  9. Su, K. Y. L.; et al. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal. 653 (1): 675–689. arXiv:astro-ph/0608563. Bibcode:2006ApJ...653..675S. doi:10.1086/508649. S2CID 14116473.
  10. Pawellek, Nicole; Krivov, Alexander V.; Marshall, Jonathan P.; Montesinos, Benjamin; Ábrahám, Péter; Moór, Attila; et al. (2014). "Disk Radii and Grain Sizes in Herschel-resolved Debris Disks". The Astrophysical Journal. 792 (1): 19. arXiv:1407.4579. Bibcode:2014ApJ...792...65P. doi:10.1088/0004-637X/792/1/65. S2CID 119282523. 65.
  11. King, Jeremy R.; Villarreal, Adam R.; Soderblom, David R.; Gulliver, Austin F.; Adelman, Saul J. (April 2003). "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group". The Astronomical Journal. 125 (4): 1980–2017. Bibcode:2003AJ....125.1980K. doi:10.1086/368241.
  12. Allen, Richard Hinckley. "Corona Borealis, the Northern Crown, Star Names — Their Lore and Meaning".
  13. "Naming Stars". International Astronomical Union. Retrieved 2018-11-02.
  14. Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  15. (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.
  16. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
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