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Quadruple star system in the constellation Hercules From Wikipedia, the free encyclopedia
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.
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[1] |
Declination | +27° 43′ 14.4379″[1] |
Apparent magnitude (V) | 3.417 ± 0.014[1] |
μ Her BC (μ2 Her) | |
Right ascension | 17h 46m 25.079s[2] |
Declination | +27° 43′ 01.45″[2] |
Apparent magnitude (V) | 10.2 / 10.7[3] |
Characteristics | |
μ Her Aab | |
Spectral type | G5IV[4] / M4V[5] |
U−B color index | +0.40[6] |
B−V color index | +0.76[6] |
μ Her BC | |
Spectral type | M3.5V[7] |
U−B color index | +1.00[6] |
B−V color index | +1.50[6] |
Astrometry | |
μ Her Aab | |
Radial velocity (Rv) | −17.07 ± 0.12[8] km/s |
Proper motion (μ) | RA: −291.66[1] mas/yr Dec.: −749.60[1] mas/yr |
Parallax (π) | 120.33 ± 0.16 mas[1] |
Distance | 27.11 ± 0.04 ly (8.31 ± 0.01 pc) |
Absolute magnitude (MV) | 3.82 ± 0.02[8] |
μ Her BC | |
Proper motion (μ) | RA: −343.35[9] mas/yr Dec.: −743.88[9] mas/yr |
Parallax (π) | 119.8871 ± 0.2055 mas[10] |
Distance | 27.21 ± 0.05 ly (8.34 ± 0.01 pc) |
Absolute magnitude (MV) | +10.26[11] |
Position (relative to μ Her Aab)[12] | |
Component | μ Her BC |
Angular distance | 35″ |
Orbit[5] | |
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[3] | |
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[8] M☉ |
Radius | 1.73 ± 0.02[8] R☉ |
Luminosity | 2.54 ± 0.08[8] L☉ |
Surface gravity (log g) | 3.98 ± 0.10[8] cgs |
Temperature | 5560 ± 80[8] K |
Metallicity [Fe/H] | 0.28 ± 0.07[8] dex |
Rotation | 52+3 −1 d[8] |
Rotational velocity (v sin i) | 1.7 ± 0.4[8] km/s |
Age | 7.8+0.3 −0.4[8] Gyr |
μ Her Ab | |
Mass | 0.32[5] M☉ |
μ Her B | |
Mass | 0.44[13] M☉ |
Radius | 0.60[14] R☉ |
Luminosity | 0.087[14] L☉ |
Temperature | 4,050[14] K |
Metallicity [Fe/H] | +0.21[14] dex |
μ Her C | |
Mass | 0.39[13] M☉ |
Other designations | |
Database references | |
SIMBAD | μ Her Aab |
μ Her BC |
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]
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]
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