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Alpha Coronae Borealis

Alpha Coronae Borealis A/B
Corona Borealis constellation map.svg
Red circle.svg

Location of α Coronae Borealis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
Right ascension 15h 34m 41.268s
Declination +26° 42′ 52.89″
Apparent magnitude (V) 2.23 (2.21 - 2.32)
Characteristics
Spectral type A0V/G5V
U−B color index –0.03
B−V color index –0.02
Variable type Eclipsing binary
Astrometry
Radial velocity (Rv) +1.7 km/s
Proper motion (μ) RA: 120.27 ± 0.19 mas/yr
Dec.: -89.58 ± 0.20 mas/yr
Parallax (π) 43.46 ± 0.28mas
Distance 75.0 ± 0.5 ly
(23.0 ± 0.1 pc)
Absolute magnitude (MV) +0.16/+5.05
Orbit
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
Mass 2.58 M
Radius 2.89–3.04 R
Luminosity 74 L
Surface gravity (log g) 3.89 cgs
Temperature 9,700 K
Rotational velocity (v sin i) 139 km/s
Age 0.314 Gyr
α CrB B
Mass 0.92 M
Radius 0.90 R
Luminosity 0.81 L
Surface gravity (log g) 4.50 cgs
Temperature 5,800 K
Rotational velocity (v sin i) < 14 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
SIMBAD data

Alpha Coronae Borealis (α Coronae Borealis, abbreviated Alpha CrB, α CrB), also named Alphecca, is a binary star in the constellation of Corona Borealis. It is located about 75 light years from the Sun.

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. 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 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 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.

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.


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Wikipedia

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