Beta Herculis (β Herculis, abbreviated Beta Her, β Her), also named Kornephoros, is a binary star and the brightest star in the northern constellation of Hercules at a base apparent visual magnitude of 2.81. This is a suspected variable star with an apparent magnitude that may rise as high as 2.76. Based upon parallax measurements, it is located at a distance of 139 light-years (43 parsecs) from the Sun.
Although Beta Herculis appears to the naked eye to be a single star, in July 1899 the American astronomer W. W. Campbell discovered from spectroscopic measurements that its radial velocity varies, and concluded that it has a companion.
At Palomar Observatory, Antoine Labeyrie and others used speckle interferometry with the Hale Telescope to resolve the system in 1977. The Hipparcos satellite observed the orbital motion of the primary relative to other stars, and an orbit was computed in 2005 using spectroscopic data together with these measurements. The period of the system is around 410 days. They have a high orbital eccentricity of 0.55 and the orbital plane is inclined 53.8° to the line of sight from the Earth.
The primary star has a stellar classification of G7 IIIa, indicating that it is a giant star that has exhausted the hydrogen at its core and evolved away from the main sequence. It has a mass nearly three times the mass of the Sun, and has expanded to 17 times the Sun's radius. The effective temperature of the star's outer envelope is about 4,887 K, which gives it the yellow hue of a G-type star. The secondary star has a mass only 90% that of the Sun.
It bore the traditional names Kornephoros, a Greek word meaning "club bearer", and Rutilicus, a corruption of the Latin word titillicus, meaning "armpit". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Kornephoros for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.
It was a member of the indigenous Arabic asterism al-Nasaq al-Shāmī, "the Northern Line" of al-Nasaqān "the Two Lines", along with Gamma Herculis, Gamma Serpentis and Beta Serpentis. Though, according to a 1971 NASA catalog, al-Nasaq al-Sha'āmī or Nasak Shamiya was the title for three other stars: Beta Serpentis as Nasak Shamiya I, Gamma Serpentis as Nasak Shamiya II and Gamma Herculis as Nasak Shamiya III.
In Chinese, 天市右垣 (Tiān Shì Yòu Yuán), meaning Right Wall of Heavenly Market Enclosure, refers to an asterism which represents eleven old states in China and which is marking the right borderline of the enclosure, consisting of Beta Herculis, Gamma Herculis, Kappa Herculis, Gamma Serpentis, Beta Serpentis, Delta Serpentis, Alpha Serpentis, Epsilon Serpentis, Delta Ophiuchi, Epsilon Ophiuchi and Zeta Ophiuchi. Consequently, Beta Herculis itself is known as 天市右垣一 (Tiān Shì Zuǒ Yòu yī, English: the First Star of Right Wall of Heavenly Market Enclosure), represent Hézhōng (河中), possibly Hezhong Municipality or Hezhong Circuit (see : Wang Chongrong, formally the Prince of Langye 瑯琊王, was a warlord of the late Chinese Tang Dynasty who controlled Hezhong Circuit, headquartered in modern Yuncheng, Shanxi). Hézhōng (河中) was westernized into Ho Chung by R.H. Allen, which means "in the river".
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv: , Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- Fernie, J. D. (May 1983), "New UBVRI photometry for 900 supergiants", Astrophysical Journal Supplement Series, 52: 7–22, Bibcode:1983ApJS...52....7F, doi:10.1086/190856
- Cayrel de Strobel, G.; Soubiran, C.; Ralite, N. (July 2001), "Catalogue of [Fe/H] determinations for FGK stars: 2001 edition", Astronomy and Astrophysics, 373: 159–163, arXiv: , Bibcode:2001A&A...373..159C, doi:10.1051/0004-6361:20010525
- HR 6148, 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 18, 2008.
- Wilson, R. E. (1953), General Catalogue of Stellar Radial Velocities, Carnegie Institute of Washington, D.C., Bibcode:1953GCRV..C......0W
- Carney, Bruce W.; et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal, 135 (3): 892–906, arXiv: , Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892
- Pan, X. P.; et al. (September 1990), "The Visual Orbit, the Stellar Diameter and the Magnitude Difference of the Spectroscopic Binary β Herculis", Bulletin of the American Astronomical Society, 22: 1335, Bibcode:1990BAAS...22R1335P
- Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
- Jancart, S.; et al. (October 2005), "Astrometric orbits of SB^9 stars", Astronomy and Astrophysics, 442 (1): 365–380, arXiv: , Bibcode:2005A&A...442..365J, doi:10.1051/0004-6361:20053003
- SV* ZI 1252 -- Spectroscopic binary, database entry, SIMBAD. Accessed on line September 18, 2008.
- Entry 16302+2129, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line September 18, 2008.
- "IAU Catalog of Star Names". Retrieved 28 July 2016.
- Kaler, James B., "Kornephoros", Stars, University of Illinois, retrieved 2008-09-18
- NSV 7778, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line September 18, 2008.
- Campbell, W. W. (1900), "The variable velocity of β Herculis in the line of sight", Astrophysical Journal, 11: 140, Bibcode:1900ApJ....11..140C, doi:10.1086/140674
- Blazit, A.; Bonneau, D.; Koechlin, L.; Labeyrie, A. (June 1, 1977), "The digital speckle interferometer: preliminary results on 59 stars and 3C 27", Astrophysical Journal Letters, 214: L79–L84, Bibcode:1977ApJ...214L..79B, doi:10.1086/182447
- HIP 80816, database entry, The Hipparcos and Tycho Catalogues, ESA, 1997, CDS ID I/239.
- "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16
- IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
- Kunitzsch, P., Smart, T. (2006), A Dictionary of Modern Star names: A Short Guide to 254 Star names and Their Derivations (Second Revised ed.), Cambridge, MA: Sky Publishing, p. 31, ISBN 1-931559-44-9
- Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 243, ISBN 0-486-21079-0, retrieved 2010-12-12
- Jack W. Rhoads - Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, Jet Propulsion Laboratory, California Institute of Technology; November 15, 1971
- (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.
- (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.
- (Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name, Hong Kong Space Museum. Accessed on line November 23, 2010.
- Star Names - R.H.Allen p. 244