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,[7] 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.[3][7] An
excess of infrared radiation at 24 μm and 70 μm has been detected about the primary star by the
IRAS.[11] This suggests the presence of a large disc of
dust and material around the star, 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).[12]
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 × 1028erg 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.[3][7]
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.[13]
It bore the traditional names Alphecca, Gemma, and Gnosia (Gnosia Stella Coronae). Alphecca is
Arabic, short for نير الفكّةnayyir 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),[citation needed] short for Gnōsia stella corōnæ "star of the crown of
Knossos".[14]Asteroth is
Hebrew, עשתרות '‘ašterôt "
Astarte (idols)" and mainly referred to the constellation.[14] As the brightest star in Corona Borealis, it lent its name to
Alphekka Meridiana, the brightest in the constellation of
Corona Australis.[citation needed] The
International Astronomical UnionWorking Group on Star Names (WGSN) has chosen Alphecca as the formal name for this star.[15]
The term nayyir al-fakka or Nir al Feccah appeared in the Al Achsasi Al Mouakket catalogue.[16]
^Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR Online Data Catalog. 2237.
Bibcode:
2002yCat.2237....0D.
^
abcdefghijklmnTomkin, 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.
^
abJohnson, 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.
^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.
^Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication: 0.
Bibcode:
1953GCRV..C......0W.