Beta Coronae Borealis

Beta Coronae Borealis (β Coronae Borealis, abbreviated Beta CrB, β CrB) is a binary star in the constellation of Corona Borealis. It appears to the naked eye to be a single star and is the second-brightest star in its constellation with an apparent visual magnitude varying between 3.65 and 3.72. Based on parallax measurements taken during the Hipparcos mission, it is approximately 112 light-years from the Sun.

Beta Coronae Borealis
Location of β Coronae Borealis (circled)
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] / F2[5]
U−B color index +0.11[6]
B−V color index +0.28[6]
V−R color index 0.2[1]
R−I color index +0.05[6]
Variable type ACV[3] roAp[5]
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 mas[7]
Distance112 ± 3 ly
(34.3 ± 0.9 pc)
Orbit[8]
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[5]
A
Mass2.09±0.15 M☉
Radius2.63±0.09 R☉
Luminosity25.3±2.9 L☉
Temperature7,980±180 K
B
Mass1.40±0.10 M☉
Radius1.56±0.07 R☉
Luminosity4.5±0.5 L☉
Surface gravity (log g)4 cgs
Temperature6,750±230 K
Metallicity [Fe/H]0.28 dex
Age530±100 Myr
Other designations
Nusakan, β CrB, Beta CrB, 3 Coronae Borealis, BD+29°2670, FK5 572, GC 20795, HD 137909, HIP 75695, HR 5747, SAO 83831, WDS 15278+2906
Database references
SIMBADdata

The two components are designated Beta Coronae Borealis A (officially named Nusakan /ˈnjuːsəkæn/, the traditional name of the system)[9][10] and B.

Nomenclature
β CrB is the 2nd-brightest star in the constellation Corona Borealis, to the right of α

β Coronae Borealis (Latinised to Beta Coronae Borealis) is the system's Bayer designation. The designations of the two components as Beta Coronae Borealis A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[11]

It bore the traditional name Nusakan, from Arabic النسقان al-nasaqān "the two lines [of stars]", originally a pair of asterisms - a northern line mostly in Hercules, and a southern line in Serpens and Ophiuchus.[9]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[12] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[13] It approved the name Nusakan for the component Beta Coronae Borealis A on 12 September 2016.[10]

In Chinese, 貫索 (Guàn Suǒ), meaning Rope Binding, refers to an asterism consisting of Beta Coronae Borealis, Pi Coronae Borealis, Theta Coronae Borealis, Alpha Coronae Borealis, Gamma Coronae Borealis, Delta Coronae Borealis, Epsilon Coronae Borealis, Iota Coronae Borealis and Rho Coronae Borealis.[14] [15] Consequently, the Chinese name for Beta Coronae Borealis itself is 貫索三 (Guàn Suǒ sān, English: the Third Star of Rope Binding).[16]

Properties
A light curve for Beta Coronae Borealis, plotted from Hipparcos data[17]

Beta Coronae Borealis was first announced to be a binary star in 1907, based on spectroscopic observations at Lick Observatory;[18] J. B. Cannon published an orbit in 1914, finding a period of 40.9 days.[19][20] 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.[20] 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.[21] A number of orbits were subsequently published using visual and speckle-interferometric observations, both alone and in conjunction with spectroscopic data.[22][23][24] In 1999, Söderhjelm published an orbit using speckle-interferometric data together with Hipparcos observations.[25]

Neubauer's 1944 work found a small variation in the radial velocity of Beta Coronae Borealis with a periodicity of 320 days, suggesting the presence of a third, lighter, body in the system.[20] 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.[26]

The brighter component, Beta Coronae Borealis A, is a rapidly oscillating Ap star, with a period of 16.2 minutes. Of spectral type A5V with a surface temperature of around 7,980 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 a main sequence star with spectral type F2, a surface temperature of around 6,750 K, 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.[5]

References
  1. "* bet CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved September 8, 2008.
  2. 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. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  4. North, P.; Carquillat, J.-M.; Ginestet, N.; Carrier, F.; Udry, S. (1998). "Multiplicity among peculiar a stars". Astronomy and Astrophysics Supplement Series. 130 (2): 223. arXiv:astro-ph/9712025. Bibcode:1998A&AS..130..223N. doi:10.1051/aas:1998365. S2CID 14002166..
  5. Bruntt, H.; Kervella, P.; Mérand, A.; Brandão, I.M.; Bedding, T.R.; ten Brummelaar, T.A.; Coudé du Foresto, V.; Cunha, M. S.; Farrington, C.; Goldfinger, P.J.; Kiss, L.L.; McAlister, H.A.; Ridgway, S.T.; Sturmann, J.; Sturmann, L.; Turner, N.; Tuthill, P.G. (2010). "The radius and effective temperature of the binary Ap star β CrB from CHARA/FLUOR and VLT/NACO observations". Astronomy and Astrophysics. 512: 7. arXiv:0912.3215. Bibcode:2010A&A...512A..55B. doi:10.1051/0004-6361/200913405. S2CID 14468327. A55.
  6. 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.
  7. van Leeuwen, F. (2007). "Validation of the New Hipparcos Reduction". Astronomy and Astrophysics. 474 (2): 653–64. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  8. Entry 15278+2906, Sixth Catalog of Orbits of Visual Binary Stars Archived 2005-04-24 at the Wayback Machine, United States Naval Observatory. Accessed on line September 9, 2008.
  9. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  10. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  12. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  13. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  14. (in Chinese) 貫索_百度百科, Baidu Baike. Accessed on line September 16, 2023.
  15. (in 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.
  16. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2011-01-30 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. "/ftp/cats/more/HIP/cdroms/cats". Centre de Données astronomiques de Strasbourg. Strasbourg astronomical Data Center. Retrieved 3 November 2022.
  18. Crawford, Russell Tracy; Champreux, A. J. (1906). "Elements and ephemeris of Comet a 1906 (Brooks)". Lick Observatory Bulletin. 4: 1. Bibcode:1906LicOB...4....1C. doi:10.5479/ADS/bib/1906LicOB.4.1C.
  19. Cannon, J. B. (1914). "Orbit of [beta] Coronae Borealis". Publications of the Dominion Observatory Ottawa. 1: 373. Bibcode:1914PDO.....1..373C.
  20. Neubauer, F. J. (1944). "The System of β Coronae Borealis". Astrophysical Journal. 99: 134. Bibcode:1944ApJ....99..134N. doi:10.1086/144602.
  21. Labeyrie, A.; Bonneau, D.; Stachnik, R. V.; Gezari, D. Y. (1974). "Speckle Interferometry. III. High-Resolution Measurements of Twelve Close Binary Systems". Astrophysical Journal. 194: L147. Bibcode:1974ApJ...194L.147L. doi:10.1086/181689.
  22. Oetken, L.; Orwert, R. (1984). "The binary nature of the magnetic star Beta CrB". Meeting on Stellar and Planetary Magnetic Fields. 305 (6): 317. Bibcode:1984AN....305..317O. doi:10.1002/asna.2113050608.
  23. Tokovinin, A. A. (1984). "Interferometer Orbits for Seven Binaries". Soviet Astronomy Letters. 10: 121. Bibcode:1984SvAL...10..121T..
  24. Kamper, Karl W.; McAlister, Harold A.; Hartkopf, William I. (1990). "Astrometric-spectroscopy binary star orbits. IV - Beta Coronae Borealis". The Astronomical Journal. 100: 239. Bibcode:1990AJ....100..239K. doi:10.1086/115510.
  25. Söderhjelm, Staffan (1999). "Visual binary orbits and masses POST HIPPARCOS". Astronomy and Astrophysics. 341: 121. Bibcode:1999A&A...341..121S.
  26. Muterspaugh, Matthew W.; Lane, Benjamin F.; Kulkarni, S. R.; Burke, Bernard F.; Colavita, M. M.; Shao, M. (2006). "Limits to Tertiary Astrometric Companions in Binary Systems". The Astrophysical Journal. 653 (2): 1469–1479. arXiv:astro-ph/0608640. Bibcode:2006ApJ...653.1469M. doi:10.1086/508743. S2CID 15218103.
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