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Mu Herculis
	; Historical view of the Hercules constellation showing Mu Herculis (μ Her) as one of stars in the hero's elbow.
Observation data; Epoch J2000 Equinox J2000
Constellation	Hercules
	μ Her Aab (μ1 Her)
Right ascension	17h 46m 27.52667s
Declination	+27° 43′ 14.4379″
Apparent magnitude (V)	3.417 ± 0.014
	μ Her BC (μ2 Her)
Right ascension	17h 46m 25.079s
Declination	+27° 43′ 01.45″
Apparent magnitude (V)	10.2 / 10.7
Characteristics
μ Her Aab
Spectral type	G5IV / M4V
U−B color index	+0.40
B−V color index	+0.76
μ Her BC
Spectral type	M3.5V
U−B color index	+1.00
B−V color index	+1.50
Astrometry
μ Her Aab
Radial velocity (Rv)	−17.07 ± 0.12 km/s
Proper motion (μ)	RA: −291.66 mas/yr ; Dec.: −749.60 mas/yr
Parallax (π)	120.33 ± 0.16 mas
Distance	27.11 ± 0.04 ly ; (8.31 ± 0.01 pc)
Absolute magnitude (MV)	3.82 ± 0.02
μ Her BC
Proper motion (μ)	RA: −343.35 mas/yr ; Dec.: −743.88 mas/yr
Parallax (π)	119.8871 ± 0.2055 mas
Distance	27.21 ± 0.05 ly ; (8.34 ± 0.01 pc)
Absolute magnitude (MV)	+10.26
Position (relative to μ Her Aab)
Component	μ Her BC
Angular distance	35″
Orbit
Primary	μ Her Aa
Companion	μ Her Ab
Period (P)	98.9 ± 22.7 yr
Semi-major axis (a)	2.9 ± 0.3″
Eccentricity (e)	0.44 ± 0.06
Inclination (i)	62.82 ± 4.66°
Longitude of the node (Ω)	80.4 ± 1.7°
Periastron epoch (T)	B 1921.1 ± 23.8
Argument of periastron (ω); (secondary)	214 ± 16°
Semi-amplitude (K1); (primary)	1.12 ± 0.10 km/s
Orbit
Primary	μ Her B
Companion	μ Her C
Period (P)	43.127 ± 0.013 yr
Semi-major axis (a)	1.385 ± 0.038″
Eccentricity (e)	0.1796 ± 0.0009
Inclination (i)	66.06 ± 0.15°
Longitude of the node (Ω)	60.07 ± 0.17°
Periastron epoch (T)	B 2008.335 ± 0.073
Argument of periastron (ω); (secondary)	172.85 ± 0.64°
Details
μ Her Aa
Mass	1.11 ± 0.01 M☉
Radius	1.73 ± 0.02 R☉
Luminosity	2.54 ± 0.08 L☉
Surface gravity (log g)	3.98 ± 0.10 cgs
Temperature	5560 ± 80 K
Metallicity [Fe/H]	0.28 ± 0.07 dex
Rotation	52+3; −1 d
Rotational velocity (v sin i)	1.7 ± 0.4 km/s
Age	7.8+0.3; −0.4 Gyr
μ Her Ab
Mass	0.32 M☉
μ Her B
Mass	0.44 M☉
Radius	0.60 R☉
Luminosity	0.087 L☉
Temperature	4,050 K
Metallicity [Fe/H]	+0.21 dex
μ Her C
Mass	0.39 M☉
Other designations
	86 Herculis, Gl 695, HR 6623, BD+27° 2888, HD 161797, LHS 3326/3325, LTT 15266, SAO 85397, FK5 667, LFT 1374, GC 24138, ADS 10786, HIP 86974.
Database references
SIMBAD	μ Her Aab
	μ Her BC

Mu Herculis (μ Herculis) is a nearby quadruple star system about 27.1 light years from Earth in the constellation Hercules. Its main star, Mu Herculis A is fairly similar to the Sun although more highly evolved with a stellar classification of G5 IV. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.^[16] Its mass is about 1.1 times that of the Sun,^[8] and it is beginning to expand to become a giant.

Etymology

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Marfak Al Jathih Al Aisr, which was translated into Latin as Cubitum Sinistrum Ingeniculi, meaning the left elbow of kneeling man.^[17]

In Chinese, 天市左垣 (Tiān Shì Zuǒ Yuán), the Left Wall of Heavenly Market Enclosure, refers to an asterism which represents eleven old states in China, marking the left borderline of the enclosure, consisting of μ Herculis, δ Herculis, λ Herculis, ο Herculis, 112 Herculis, ζ Aquilae, θ¹ Serpentis, η Serpentis, ν Ophiuchi, ξ Serpentis and η Ophiuchi.^[18] Consequently, the Chinese name for μ Herculis itself is 天市左垣三 (Tiān Shì Zuǒ Yuán sān, English: the Third Star of Left Wall of Heavenly Market Enclosure), represent Jiuhe (九河, lit. meaning nine rivers), possibly for Jiujiang, the prefecture-level city in Jiangxi, China, which is the same literally meaning with Jiuhe.^[19]^[20] From this Chinese title, the name Kew Ho appeared.^[21]

Star system

Mu Herculis is a quadruple star system. The brightest star is a well-studied G-type subgiant, whose parameters are precisely determined from asteroseismology.^[8] It was believed to be a close binary with a low-mass stellar or a large substellar companion. This was confirmed when low-mass companion was resolved using near-infrared spectroscopy.^[5] The companion star is a red dwarf with a spectral type of M4V and a mass of 0.32 M_☉.^[5] This pair is also known as Mu¹ Herculis.

The secondary component, also known as Mu² Herculis,^[12] consists of a pair of stars that orbit about each other with a period of about 43 years.^[22] Mu Herculis A and the binary pair B-C are separated by some 35 arcseconds.^[15] The stars B and C, which orbit each other, are separated from each other by 1.385 arcseconds, and have a slightly eccentric orbit, at 0.1796.^[3]

References

^ ^a ^b ^c ^d ^e ^f van Leeuwen, F. (November 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, S2CID 18759600
^ ^a ^b Cutri, R. M.; et al. (2003). "2MASS All-Sky Catalog of Point Sources". VizieR On-line Data Catalog. 2246. Bibcode:2003yCat.2246....0C.
^ ^a ^b ^c "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 23 March 2017.
^ Yang, Wuming; Meng, Xiangcun (April 2010), "Models of μ Her with asteroseismic constraints", New Astronomy, 15 (4): 367–372, arXiv:0911.0749, Bibcode:2010NewA...15..367Y, doi:10.1016/j.newast.2009.11.001, S2CID 119121800
^ ^a ^b ^c ^d ^e Roberts Jr., Lewis C.; Mason, Brian D.; Aguilar, Jonathan; Carson, Joseph; Crepp, Justin; Beichman, Charles; Brenner, Douglas; Burruss, Rick; Cady, Eric; Luszcz-Cook, Statia; Dekany, Richard; Hillenbrand, Lynne; Hinkley, Sasha; King, David; Lockhart, Thomas G.; Nilsson, Ricky; Oppenheimer, Rebecca; Parry, Ian R.; Pueyo, Laurent; Rice, Emily L.; Sivaramakrishnan, Anand; Soummer, Rémi; Vasisht, Gautam; Veicht, Aaron; Wang, Ji; Zhai, Chengxing; Zimmerman, Neil T. (2016). "Characterization of the Companion to μ Her". The Astronomical Journal. 151 (6): 169. arXiv:1604.06494. Bibcode:2016AJ....151..169R. doi:10.3847/0004-6256/151/6/169. S2CID 43403927.
^ ^a ^b ^c ^d Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data: 0. Bibcode:1986EgUBV........0M.
^ Alonso-Floriano, F. J.; Morales, J. C.; Caballero, J. A.; Montes, D.; Klutsch, A.; Mundt, R.; Cortés-Contreras, M.; Ribas, I.; Reiners, Ansgar; Amado, P. J.; Quirrenbach, A.; Jeffers, S. V. (2015). "CARMENES input catalogue of M dwarfs" (PDF). Astronomy & Astrophysics. 577: A128. arXiv:1502.07580. Bibcode:2015A&A...577A.128A. doi:10.1051/0004-6361/201525803. S2CID 53135130.^{[permanent dead link‍]}
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Grundahl, F.; Andersen, M. Fredslund; Christensen-Dalsgaard, J.; Antoci, V.; Kjeldsen, H.; Handberg, R.; Houdek, G.; Bedding, T. R.; Pallé, P. L.; Jessen-Hansen, J.; Aguirre, V. Silva; White, T. R.; Frandsen, S.; Albrecht, S.; Andersen, M. I.; Arentoft, T.; Brogaard, K.; Chaplin, W. J.; Harpsøe, K.; Jørgensen, U. G.; Karovicova, I.; Karoff, C.; Rasmussen, P. Kjærgaard; Lund, M. N.; Lundkvist, M. Sloth; Skottfelt, J.; Norup Sørensen, A.; Tronsgaard, R.; Weiss, E. (2017). "First Results from the Hertzsprung SONG Telescope: Asteroseismology of the G5 Subgiant Star μ Herculis". The Astrophysical Journal. 836 (1): 142. arXiv:1701.03365. Bibcode:2017ApJ...836..142G. doi:10.3847/1538-4357/836/1/142. S2CID 119480210.
^ ^a ^b Röser, S.; Schilbach, E.; Schwan, H.; Kharchenko, N. V.; Piskunov, A. E.; Scholz, R.-D. (2008). "PPM-Extended (PPMX) – a catalogue of positions and proper motions". Astronomy and Astrophysics. 488 (1): 401. arXiv:0806.1009. Bibcode:2008A&A...488..401R. doi:10.1051/0004-6361:200809775. S2CID 17350617.
^ Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
^ Davison, Cassy L.; White, R. J.; Henry, T. J.; Riedel, A. R.; Jao, W. -C.; Bailey, J. I.; Quinn, S. N.; Cantrell, J. R.; Subasavage, J. P.; Winters, J. G. (2015). "A 3D Search for Companions to 12 Nearby M Dwarfs". The Astronomical Journal. 149 (3): 106. arXiv:1501.05012. Bibcode:2015AJ....149..106D. doi:10.1088/0004-6256/149/3/106. S2CID 9719725.
^ ^a ^b "* mu.02 Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 May 2017.
^ ^a ^b "Multiple Star Catalog". Archived from the original on 2018-12-03. Retrieved 2018-12-02.
^ ^a ^b ^c ^d Gaidos, E.; Mann, A. W.; Lépine, S.; Buccino, A.; James, D.; Ansdell, M.; Petrucci, R.; Mauas, P.; Hilton, E. J. (2014). "Trumpeting M dwarfs with CONCH-SHELL: A catalogue of nearby cool host-stars for habitable exoplanets and life". Monthly Notices of the Royal Astronomical Society. 443 (3): 2561. arXiv:1406.7353. Bibcode:2014MNRAS.443.2561G. doi:10.1093/mnras/stu1313.
^ ^a ^b "* mu. Her". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 24 May 2017.
^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society, 25: 1319, Bibcode:1993AAS...183.1710G, archived from the original on 2019-06-25, retrieved 2012-02-04
^ 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 (8): 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429
^ (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.
^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 23 日 Archived 2021-05-15 at the Wayback Machine
^ (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived 2010-08-10 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
^ Star Name - R.H. Allen p. 238
^ Turner, Nils H.; et al. (June 2001), "Search for Faint Companions to Nearby Solar-like Stars using the Adaptive Optics System at Mount Wilson Observatory", The Astronomical Journal, 121 (6): 3254–3258, Bibcode:2001AJ....121.3254T, doi:10.1086/321075