Beta Coronae Borealis

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β Coronae Borealis

β (circled) in the constellation Corona Borealis.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Borealis
Right ascension 15h 27m 49.7308s[1][2]
Declination +29° 06′ 20.530″[1][2]
Apparent magnitude (V) 3.65 to 3.72[3]
Characteristics
Spectral type A9SrEuCr / ?[4]
U−B color index +0.11[5]
B−V color index +0.28[5]
V−R color index 0.2[1]
R−I color index +0.05[5]
Variable type ACV[3]
Astrometry
Radial velocity (Rv) −18.7 ± 0.9[1] km/s
Proper motion (μ) RA: −181.39[1][2] mas/yr
Dec.: 86.84[1][2] mas/yr
Parallax (π) 29.17 ± 0.76[6] mas
Distance 112 ± 3 ly
(34.3 ± 0.9 pc)
Orbit[7]
Period (P) 10.27 ± 0.14 y
Semi-major axis (a) 0.205 ± 0.002″
Eccentricity (e) 0.524 ± 0.006
Inclination (i) 111.1 ± 0.9°
Longitude of the node (Ω) 148.2 ± 0.5°
Periastron epoch (T) B1980.506 ± 0.014
Argument of periastron (ω)
(secondary)		 181.3 ± 0.7°
Details[8]
A
Mass 2.09 ± 0.15 M☉
Radius 2.63 ± 0.09 R☉
Luminosity 25.3 ± 2.9 L☉
Temperature 7,980 ± 180 K
B
Mass 1.40 ± 0.10 M☉
Radius 1.56 ± 0.07 R☉
Luminosity 4.5 ± 0.5 L☉
Surface gravity (log g) 4 cgs
Temperature 6,750 ± 230 K
Age 530 ± 100 Myr
Other designations
Nusakan,[9] β CrB, Beta Coronae Borealis, 3 CrB, BD+29°2670, FK5 572, GC 20795, HD 137909, HIP 75695, HR 5747, SAO 83831, WDS 15278+2906
Database references
SIMBAD data

Beta Coronae Borealis (Beta CrB, β Coronae Borealis, β CrB), 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. It is 112±3 light-years away and has an apparent visual magnitude which varies between 3.65 and 3.72.

In Chinese, 貫索 (Guàn Suǒ), meaning Coiled Thong, refers to an asterism consisting of β Coronae Borealis, π Coronae Borealis, θ Coronae Borealis, α Coronae Borealis, γ Coronae Borealis, δ Coronae Borealis, ε Coronae Borealis, ι Coronae Borealis and ρ Coronae Borealis.[10] Consequently, β Coronae Borealis itself is known as 貫索三 (Guàn Suǒ sān, English: the Third Star of Coiled Thong.).[11]

Properties

β Coronae Borealis was first announced to be a binary star in 1907, based on spectroscopic observations at Lick Observatory;[12] J. B. Cannon published an orbit in 1914, finding a period of 40.9 days.[13][14] Later spectroscopic investigations by F. J. Neubauer at Lick, published in 1944, found a period of 10.5 years, with no evidence for the 41-day periodicity.[14] Antoine Labeyrie and his coworkers resolved the pair by speckle interferometry in 1973 and found that the two stars were separated by about 0.25 arcseconds; this work was published in 1974. The pair was also observed visually by Coteau in 1973.[15] A number of orbits were subsequently published using visual and speckle-interferometric observations, both alone and in conjunction with spectroscopic data.[16][17][18] In 1999, Söderhjelm published an orbit using speckle-interferometric data together with Hipparcos observations.[19]

Neubauer's 1944 work found a small variation in the radial velocity of β Coronae Borealis with a periodicity of 320 days, suggesting the presence of a third, lighter, body in the system.[14] A 1999 study of the system by long-baseline infrared interferometry performed at Palomar Observatory found no evidence for this, and showed that any tertiary companion with this period must have mass 10 Jupiter masses or below. This study also found very weak evidence for the presence of a companion with a shorter, 21-day, period, but the data was insufficient to draw a positive conclusion.[20]

The brighter component is a Rapidly oscillating Ap star, with a period of 16.2 minutes. Of spectral type A5V with a surface temperature of around 7980 K, it has around 2.09 times the mass of the Sun, 2.63 times its radius and 25.3 times its luminosity. The smaller star is of spectral type F2V with a surface temperature of around 6750 K, and has around 1.4 times the mass of the Sun, 1.56 times its radius and between 4 and 5 times its luminosity. The system is around 530 million years old.[8]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 V* bet CrB -- Spectroscopic binary, database entry, SIMBAD. Accessed on line September 8, 2008.
  2. ↑ 2.0 2.1 2.2 2.3 Astrometric data, mirrored by SIMBAD from the Hipparcos catalogue, pertains to the center of mass of the β Coronae Borealis binary system. See §2.3.4, Volume 1, The Hipparcos and Tycho Catalogues, European Space Agency, 1997, and the entry in the Hipparcos catalogue (CDS ID I/239.)
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found..
  5. ↑ 5.0 5.1 5.2 HR 5747, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line September 8, 2008.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Entry 15278+2906, Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory. Accessed on line September 9, 2008.
  8. ↑ 8.0 8.1 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ (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.
  11. ↑ (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.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ 14.0 14.1 14.2 Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found..
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
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