Alpha Coronae Borealis (α Coronae Borealis, abbreviated Alpha CrB, α CrB), officially named Alphecca , is an eclipsing binary star in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Corona Borealis. It is located about 75

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s from the Sun and contains two

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

stars, one class A and one class G.

Properties

Alpha Coronae Borealis is a binary system, its stars orbiting each other in an

eccentric orbit In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betw ...

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, 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

star that has a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of A0V and 2.6 times the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

. Estimates of the star's radius range from 2.89 to 3.04 times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\t ...

. An excess of infrared radiation at 24 μm and 70 μm has been detected about the primary star by the IRAS. 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). 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 , 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. The space velocity components of this star system are U =, V = and W =. α CrB is believed to be a member of the Ursa Major Moving Group of stars that have a common motion through space.

Nomenclature

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

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

. It bore the traditional names ''Alphecca'', ''Gemma'', and ''Gnosia'' (Gnosia Stella Coronae). ''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". ''Asteroth'' is Hebrew, עשתרות ‘ašterôt'' " Astarte (idols)" and mainly referred to the constellation. 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 formal name for this star. The term ''nayyir al-fakka'' or ''Nir al Feccah'' appeared in the Al Achsasi Al Mouakket catalogue. In Chinese, (), meaning '' Coiled Thong'', refers to an asterism consisting of Alpha Coronae Borealis,

Pi Coronae Borealis Pi Coronae Borealis, Latinized from π Coronae Borealis, is a solitary, orange-hued star in the northern constellation of Corona Borealis. Its apparent magnitude is 5.58, which is bright enough to be faintly visible to the naked eye. Base ...

, Theta Coronae Borealis,

Beta Coronae Borealis Beta Coronae Borealis (β Coronae Borealis, abbreviated Beta CrB, β CrB) is a binary star in the constellation of Corona Borealis. It appears to the naked eye to be a single star and is the second-brightest ...

, Gamma Coronae Borealis, Delta Coronae Borealis,

Epsilon Coronae Borealis Epsilon Coronae Borealis, Latinized from ε Coronae Borealis, is a multiple star system in the constellation Corona Borealis located around 230 light-years from the Solar System. It shines with a combined apparent magnitude of 4.13, me ...

Iota Coronae Borealis Iota Coronae Borealis, Latinized from ι Coronae Borealis, is a binary star system in the constellation Corona Borealis. It is visible to the naked eye with a combined apparent visual magnitude of is 4.96. Based upon an annual parallax ...

and

Rho Coronae Borealis Rho Coronae Borealis (ρ CrB, ρ Coronae Borealis) is a yellow dwarf star 56 light-years away in the constellation of Corona Borealis. The star is thought to be similar to the Sun with nearly the same mass, radius, and luminosity. It ...

. Consequently, the Chinese name for Alpha Coronae Borealis itself is (, en, the Fourth Star of Coiled Thong.).

References

{{DEFAULTSORT:Alpha Coronae Borealis G-type main-sequence stars A-type main-sequence stars Eclipsing binaries Ursa Major Moving Group

Alphecca Alpha Coronae Borealis (α Coronae Borealis, abbreviated Alpha CrB, α CrB), officially named Alphecca , is an eclipsing binary star in the constellation of Corona Borealis. It is located about 75 light years from the Sun and contains tw ...

Corona Borealis Coronae Borealis, Alpha Durchmusterung objects Coronae Borealis, 05 139006 076267 5793