Alpha Coronae Borealis
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 Location of α Corona Borealis. |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Corona Borealis |
| Right ascension | 15h 34m 41.2681s[1] |
| Declination | +26° 42′ 52.895″[1] |
| Apparent magnitude (V) | 2.21 (2.24 / 7.1) |
| Characteristics | |
| Spectral type | A0V/G5V[2] |
| U-B color index | –0.03[3]/— |
| B-V color index | –0.02[3]/— |
| Variable type | Eclipsing binary |
| Astrometry | |
| Radial velocity (Rv) | +1.7[4] km/s |
| Proper motion (μ) | RA: +120.38[1] mas/yr Dec.: –89.44[1] mas/yr |
| Parallax (π) | 43.65 ± 0.79[1] mas |
| Distance | 75 ± 1 ly (22.9 ± 0.4 pc) |
| Absolute magnitude (MV) | +0.16/+5.05[2] |
| Orbit[5] | |
| Period (P) | 17.3599 d |
| Semimajor axis (a) | 2.981 × 1012 cm |
| Eccentricity (e) | 0.370 |
| Inclination (i) | 88.2 ± 0.1° |
| Argument of periastron (ω) (primary) |
311° |
| Details | |
| Mass | 2.58/0.92[2] M☉ |
| Radius | 2.89–3.04/0.90[2][5] R☉ |
| Surface gravity (log g) | 3.89/4.50[2] |
| Luminosity | 74/0.81[2] L☉ |
| Temperature | 9,700/5,800[2] K |
| Rotational velocity (v sin i) | 139[6] / < 14[5] km/s |
| Age | 3.14 × 108 years |
| Other designations | |
| Database references | |
| SIMBAD | data |
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.
It has the traditional names Alphecca (Alphekka), Gemma, Gnosia (Gnosia Stella Coronae), and Asteroth (Ashtaroth). The name 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 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 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.[2][5] An excess of infrared radiation at 24 μm and 70 μm has been detected about the primary star by the IRAS.[7] 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. How the binary-star dynamic would affect such a system is the subject of intense debate.[citation needed]
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 × 1028 erg 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.[2][5]
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,[5] 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,[8] which is hardly noticeable to the unaided eye.
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.[9]
In astrology it is one of the Behenian fixed stars and has the symbol 
.[citation needed]
[edit] References
- ^ a b c d e Perryman, M. A. C.; et al (April 1997). "The HIPPARCOS Catalogue". Astronomy & Astrophysics 323: L49–L52. Bibcode: 1997A&A...323L..49P.
- ^ a b c d e f g h i Tomkin, 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.
- ^ a b Johnson, 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). Bibcode: 1966CoLPL...4...99J.
- ^ Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington D.C.. http://adsabs.harvard.edu/abs/1953GCRV..C......0W. Retrieved 2009-09-08.
- ^ a b c d e f Güdel, M.; Arzner, K.; Audard, M.; Mewe, R. (May 2003). "Tomography of a stellar X-ray corona: alpha Coronae Borealis". Astronomy and Astrophysics 403: 155-171. doi:10.1051/0004-6361:20030257. Bibcode: 2003A&A...403..155G.
- ^ Royer, F.; Grenier, S.; Baylac, M.-O.; Gómez, A. E.; Zorec, J. (October 2002). "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i". Astronomy and Astrophysics 393: 897–911. doi:10.1051/0004-6361:20020943. Bibcode: 2002A&A...393..897R. Table 8.
- ^ Su, K. Y. L.; et al. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal 653 (1): 675-689. doi:10.1086/508649. Bibcode: 2006ApJ...653..675S.
- ^ Efremov, N.; et al. (1971). General Catalogue of Variable Stars (3rd ed.). Moscow.
- ^ King, Jeremy R.; Villarreal, Adam R.; Soderblom, David R.; Gulliver, Austin F.; Adelman, Saul J. (April 2003). "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group". The Astronomical Journal 125 (4): 1980-2017. doi:10.1086/368241. Bibcode: 2003AJ....125.1980K.
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