Alpha Coronae Borealis

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Alpha Coronae Borealis A/B
Corona borealis constellation map.png
Locator Dot2.gif

The red dot shows the location of α Corona Borealis.
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
Right ascension 15h 34m 41.268s[1]
Declination +26° 42′ 52.89″[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: 120.27 ± 0.19[1] mas/yr
Dec.: -89.58 ± 0.20[1] mas/yr
Parallax (π) 43.46 ± 0.28[1] mas
Distance 75.0 ± 0.5 ly
(23.0 ± 0.1 pc)
Absolute magnitude (MV) +0.16/+5.05[2]
Orbit[5]
Period (P) 17.3599 d
Semi-major 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
Luminosity 74/0.81[2] L
Surface gravity (log g) 3.89/4.50[2] cgs
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
Gemma, Alphekka, Alphecca, Gnosia, Ashtaroth, The Jewel, Gnosia Stella Coronae, 5 CrB, HR 5793, BD +27°2512, HD 139006, GCTP 3519.00, SAO 83893, FK5 578, HIP 76267.
Database references
SIMBAD data

Alpha Coronae Borealis (α CrB, α Coronae Borealis, Alphecca) is a binary star in the constellation Corona Borealis. It is located about 75 light years from the Solar System.

Properties[edit]

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.

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]

Name[edit]

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 term nayyir al-fakka or Nir al Feccah was appeared in Al Achsasi Al Mouakket catalogue.[10]

In Chinese, 貫索 (Guàn Suǒ), 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.[11] Consequently, α Coronae Borealis itself is known as 貫索四 (Guàn Suǒ sì, English: the Fourth Star of Coiled Thong.).[12]

See also[edit]

References[edit]

  1. ^ a b c d e van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.  Vizier catalog entry
  2. ^ 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. Bibcode:1986AJ.....91.1428T. doi:10.1086/114121. 
  3. ^ 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. 
  4. ^ Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington, D.C. Retrieved 2009-09-08. 
  5. ^ 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. Bibcode:2003A&A...403..155G. doi:10.1051/0004-6361:20030257. 
  6. ^ 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. arXiv:astro-ph/0205255. Bibcode:2002A&A...393..897R. doi:10.1051/0004-6361:20020943.  Table 8.
  7. ^ Su, K. Y. L.; et al. (December 2006). "Debris Disk Evolution around A Stars". The Astrophysical Journal 653 (1): 675–689. arXiv:astro-ph/0608563. Bibcode:2006ApJ...653..675S. doi:10.1086/508649. 
  8. ^ Efremov, N.; et al. (1971). General Catalogue of Variable Stars (3rd ed.). Moscow. 
  9. ^ 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. Bibcode:2003AJ....125.1980K. doi:10.1086/368241. 
  10. ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 429. Bibcode:1895MNRAS..55..429K. 
  11. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  12. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.