Alpha Coronae Borealis
Encyclopedia
Alpha Coronae Borealis (α CrB, α Coronae Borealis) is a binary star
in the constellation
Corona Borealis
. It is located about 75 light years from the Solar System
.
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. 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 Alphecca, prompting speculation of a planetary or proto-planetary system similar to that currently assumed around Vega
.
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 stars are orbiting about each other in an eccentric orbit one 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 an 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 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.
, short for نير الفكّة nayyir al-fakka "the bright (star) of the broken (ring of stars)". Gemma is Latin for "jewel". Gnosia is also Latin, short for Gnōsia stella corōnæ "star of the crown of Knossos
". Asteroth is Hebrew, עשתרות ‘ašterôt "Astarte
(idols)". As the brightest star in Corona Borealis, it lent its name to the brightest in Corona Australis
, Alphekka Meridiana.
The term nayyir al-fakka or Nir al Feccah was appeared in Al Achsasi Al Mouakket catalogue.
In Chinese, , meaning Coiled Thong
, refers to an asterism consisting of α Coronae Borealis, π Coronae Borealis, θ Coronae Borealis, β Coronae Borealis
, γ Coronae Borealis, δ Coronae Borealis, ε Coronae Borealis, ι Coronae Borealis and ρ Coronae Borealis
. Consequently, α Coronae Borealis itself is known as .
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Corona Borealis
Corona Borealis
Corona Borealis is a small constellation in the northern sky. Its name is Latin for "northern crown", a name inspired by its shape; its main stars form a semicircular arc. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and remains one of the 88 modern...
. It is located about 75 light years from the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
.
Properties
The primary component is a white main sequenceMain sequence
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 Hertzsprung and Henry Norris Russell...
star that has a stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
of A0V and 2.6 times the mass of the Sun
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
. Estimates of the star's radius range from 2.89 to 3.04 times the radius of the Sun. An excess of infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation at 24 μm and 70 μm has been detected about the primary star by the IRAS
IRAS
The Infrared Astronomical Satellite was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths....
. This suggests the presence of a large disc of dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
and material around Alphecca, prompting speculation of a planetary or proto-planetary system similar to that currently assumed around Vega
Vega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
.
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
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
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
Corona
A corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
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 stars are orbiting about each other in an eccentric orbit one 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 an 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 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
Ursa Major Moving Group
The Ursa Major Moving Group, also known as Collinder 285 or Ursa Major association, is a nearby stellar moving group, a set of stars with common velocities in space and thought to have a common origin. Its core is located roughly 80 light years away...
of stars that have a common motion through space.
Name
It has the traditional names Alphecca (Alphekka), Gemma, Gnosia (Gnosia Stella Coronae), and Asteroth (Ashtaroth). The name Alphecca is ArabicArabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...
, short for نير الفكّة nayyir al-fakka "the bright (star) of the broken (ring of stars)". Gemma is Latin for "jewel". Gnosia is also Latin, short for Gnōsia stella corōnæ "star of the crown of Knossos
Knossos
Knossos , also known as Labyrinth, or Knossos Palace, is the largest Bronze Age archaeological site on Crete and probably the ceremonial and political centre of the Minoan civilization and culture. The palace appears as a maze of workrooms, living spaces, and store rooms close to a central square...
". Asteroth is Hebrew, עשתרות ‘ašterôt "Astarte
Astarte
Astarte is the Greek name of a goddess known throughout the Eastern Mediterranean from the Bronze Age to Classical times...
(idols)". As the brightest star in Corona Borealis, it lent its name to the brightest in Corona Australis
Corona Australis
Corona Australis or Corona Austrina is a constellation. Its name means "southern crown", and it contrasts with Corona Borealis, the northern crown...
, Alphekka Meridiana.
The term nayyir al-fakka or Nir al Feccah was appeared in Al Achsasi Al Mouakket catalogue.
In Chinese, , meaning Coiled Thong
Heavenly Market enclosure
Tian Shi Yuan, the Heavenly Market Enclosure , is one of the San Yuan or Three enclosures. Stars and constellations of this group are visible during late summer and early autumn in the Northern Hemisphere . The summer triangle lies directly to the northwest.-Asterisms:The asterisms are :...
, refers to an asterism consisting of α Coronae Borealis, π Coronae Borealis, θ Coronae Borealis, β Coronae Borealis
Beta Coronae Borealis
Beta Coronae Borealis , which has the traditional name Nusakan, is the second brightest star in the constellation of Corona Borealis. Although it appears to the naked eye to be a single star, it is actually a binary star system...
, γ Coronae Borealis, δ Coronae Borealis, ε Coronae Borealis, ι Coronae Borealis and ρ Coronae Borealis
Rho Coronae Borealis
Rho Coronae Borealis is a Solar twin, yellow dwarf star approximately 57 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. As of 1997, an extrasolar planet has been confirmed to be orbiting the...
. Consequently, α Coronae Borealis itself is known as .