|Alpha Coronae Borealis|
α Coronae Borealis
5 Coronae Borealis
|Right ascension||15h 34m 41.2680s|
|Declination||+26° 42′ 52.8940″|
|Type of object||Main sequence star|
|Magnitude|| Apparent Mag: +2.22|
Absolute Mag: 0.41
|Distance from Earth||75 ly|
|Radial velocity||1.7±0.9 km/s|
|Proper motion|| RA: 120.27 mas/yr|
Dec.: -89.58 mas/yr
Alpha Coronae Borealis (Alphecca, α Coronae Borealis, α CrB, 5 Coronae Borealis) is a main sequence star in the constellation of Corona Borealis, the Northern Crown. The star is known by several names: Alphecca (which roughly translates as “the bright one of the broken ring” in Arabic), Gemma (“jewel” in Latin), Asteroth (“idols” in Hebrew), and Gnosia (short for “Gnosia stella coronae,” or “the star of the crown of Knossos” in Latin). The star is in fact one star in a binary system of two stars. The brightest star in the Northern Crown, it was first catalogued in the 2nd century by the Greek astronomer, Ptolemy. The star is bright enough to be seen with the unaided eye and is best observed in the mid-northern latitudes between April, May and June. It can be found by drawing an imaginary line from Arcturus to Vega.
Situated approximately 75 light years from Earth, Alpha Coronae Borealis a white star belonging to spectral class A0V. Its spectrum shows a large excess of infrared radiation, thought to be caused by a disk of dust and other material surrounding the star. Such a disc may contain planets. The star is 67 times more luminous than the Sun and possess a radius 2.7 times as large. Its mass is estimated at 2.7 solar masses and it has a high surface temperature of 10,000 kelvin. The star rotates quickly, with a speed of 110 km/s, though other sources put it higher at 127-133 km/s.
Alpha Coronae Borealis is part of a binary system and orbits its companion star every 17.3599 days. Alpha Coronae Borealis is sometimes referred to as Alphecca-A to distinguish it from the system or the companion which is then designated Alphecca-B. The average separation between the stars is 0.20 AU (smaller than the distance between the Sun and Mercury), though the eccentricity of the orbit of e=0.35 means it varies from 0.13 AU up to 0.27 AU. These two stars are believed to be part of the Ursa Major Moving Group, a collection of stars in Ursa Major that share a common motion through space.
Alphecca-B is a main sequence star with spectral class G5 and is an 8th magnitude star, too dim to be seen with the naked eye. The system is classified as an EA variable, meaning the brightness of Alpha Coronae Borealis varies as it is eclipsed by its companion from +2.21 up to +2.32. The companion star is smaller than Alpha Coronae Borealis with a mass of 0.92 solar masses and radius of 0.9 that of Sol. Alphecca-B is a powerful x-ray source, though to be caused by "solar-like magnetic activity".
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- Eccentricity computed using amin = (1-e)a, with amin = 0.13 AU, a = 0.2 AU.
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