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Beta Coronae Borealis (Beta CrB, β Coronae Borealis, β CrB), which has the traditional name Nusakan,〔The name is Arabic, apparently ألنسفان ''an-nasaqan'' "the (two) series".〕 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.〔(Nusakan ), ''Stars'', Jim Kaler. Accessed on line October 14, 2013.〕 It is 112±3 light-years away and has an apparent visual magnitude which varies between 3.65 and 3.72.〔〔 In Chinese, (), 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.〔 ''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.〕 Consequently, β Coronae Borealis itself is known as (, (英語:the Third Star of Coiled Thong).).〔 (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.〕 ==Properties== β Coronae Borealis was first announced to be a binary star in 1907, based on spectroscopic observations at Lick Observatory;〔(A list of six stars whose radial velocities vary ), W. W. Campbell and J. H. Moore, ''Lick Observatory Bulletin'' 4 , #123 (1907), pp. 161–162.〕 J. B. Cannon published an orbit in 1914, finding a period of 40.9 days.〔Orbit of beta Coronae Borealis, J. B. Cannon, ''Publications of the Dominion Observatory, Ottawa'' 1 (1914), pp. 373–405, .〕〔The System of β Coronae Borealis, F. J. Neubauer, ''Astrophysical Journal'' 99 (March 1944), pp. 134–144, .〕 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.〔 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.〔Speckle Interferometry. III. High-Resolution Measurements of Twelve Close Binary Systems, A. Labeyrie, D. Bonneau, R. V. Stachnik, and D. Y. Gezari, ''Astrophysical Journal'' 194 (December 15, 1974), pp. L147–L151, .〕 A number of orbits were subsequently published using visual and speckle-interferometric observations, both alone and in conjunction with spectroscopic data.〔The Binary Nature of the Magnetic Star β CrB, L. Oetken and R. Orwert, ''Astronomische Nachrichten'' 305, #6 (1984), pp. 317–323, 〕〔Interferometer Orbits for Seven Binaries, A. A. Tokovinin, ''Soviet Astronomy Letters'' 10, #2 (March–April 1984), pp. 121–123, .〕〔Astrometric-spectroscopy binary star orbits. IV - Beta Coronae Borealis, Karl W. Kamper, Harold A. McAlister, and William I. Hartkopf, ''Astronomical Journal'' 100, #1 (July 1990), pp. 239–246, , .〕 In 1999, Söderhjelm published an orbit using speckle-interferometric data together with Hipparcos observations.〔Visual binary orbits and masses post Hipparcos, Staffan Söderhjelm, ''Astronomy and Astrophysics'' 341 (January 1999), pp. 121–140, .〕 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.〔 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.〔§7, Limits to Tertiary Astrometric Companions in Binary Systems, Matthew W. Muterspaugh, Benjamin F. Lane, S. R. Kulkarni, Bernard F. Burke, M. M. Colavita, and M. Shao, ''Astrophysical Journal'' 653, #2 (December 2006), pp. 1469–1479, , .〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Beta Coronae Borealis」の詳細全文を読む スポンサード リンク
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