Historical view of the Hercules constellation showing Mu Herculis (μ Her) as one of stars in the hero's elbow.
Epoch J2000 Equinox J2000
|Right ascension||17h 46m 27.52667s|
|Declination||+27° 43′ 14.4379″|
|Apparent magnitude (V)||3.417 ± 0.014/10.35/10.80|
|Spectral type||G5 IV/M3.5 V/M4 V|
|U−B color index||0.39/1.01|
|B−V color index||0.75/1.50|
|Radial velocity (Rv)||−16.1/-13.7 km/s|
|Proper motion (μ)||RA: −291.66/-77.62 mas/yr
Dec.: −749.60/-270.12 mas/yr
|Parallax (π)||120.33 ± 0.16 mas|
|Distance||27.11 ± 0.04 ly
(8.31 ± 0.01 pc)
|Absolute magnitude (MV)||3.80/10.73/11.18|
|μ Her A|
|Radius||1.77 ± 0.07 R☉|
|Luminosity||2.70 ± 0.16 L☉|
|Surface gravity (log g)||3.70 cgs|
|Temperature||5,596 ± 80 K|
|Metallicity [Fe/H]||0.21 ± 0.07 dex|
|Rotational velocity (v sin i)||20 km/s|
|Age||6.43 ± 0.04 Gyr|
|μ Her BC|
Mu Herculis (μ Herculis) is a nearby 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. Its mass is about 1.1 times that of the Sun, and it is beginning to expand to become a giant.
The secondary component consists of a pair of stars that orbit about each other with a period of 43.2 years. Mu Herculis A and the binary pair B-C are separated by 286 AUs. The stars B-C are separated from each other by 11.4 AUs. Their orbit is quite elliptic (e=0.18) and both stars swing each other between 9.4 and 13.5 AUs.
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.
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. Consequently, μ Herculis itself is known as 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. From this Chinese title, the name Kew Ho appeared.
Star A is itself suspected to be a close binary with a low mass stellar or a large substellar companion, probably at 17.2 AU in an elliptic orbit. Nevertheless the existence of such an object has still not been confirmed.
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