Astronomy:Mu Herculis

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Short description: Quadruple star system in the constellation Hercules

Coordinates: Sky map 17h 46m 27.52667s, +27° 43′ 14.4379″

μ Herculis
Location of μ Herculis (circled in red)
Observation data
{{#ifeq:J2000|J2000.0 (ICRS)|Epoch J2000.0      Equinox J2000.0 (ICRS)| Epoch J2000      [[Astronomy:Equinox (celestial coordinates)|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] / M4±1V[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)120.069 ± 0.089[9] mas
Distance27.16 ± 0.02 ly
(8.329 ± 0.006 pc)
Absolute magnitude (MV)3.82 ± 0.02[8]
μ Her BC
Proper motion (μ) RA: −343.35[10] mas/yr
Dec.: −743.88[10] mas/yr
Absolute magnitude (MV)+10.26[11]
Orbit[9]
Primaryμ Her A
Companionμ Her BC
Period (P)12905.46+421.70
−608.68 yr
Semi-major axis (a)1132+25
−33 AU
Eccentricity (e)0.879±0.004
Inclination (i)79.58±0.21°
Longitude of the node (Ω)238.05±0.34°
Periastron epoch (T)4690500.10+77254.66
−110823.59
Argument of periastron (ω)
(secondary)		290.6±0.8°
Orbit[9]
Primaryμ Her Aa
Companionμ Her Ab
Period (P)78.987±0.288 yr
Semi-major axis (a)20.418±0.050 AU
Eccentricity (e)0.379±0.001
Inclination (i)62.39±0.07°
Longitude of the node (Ω)267.50±0.06°
Periastron epoch (T)2460156.6±7.3
Argument of periastron (ω)
(secondary)		50.303±0.224°
Orbit[9]
Primaryμ Her B
Companionμ Her C
Period (P)43.141±0.008 yr
Semi-major axis (a)11.705±0.031 AU
Eccentricity (e)0.179±0.001
Inclination (i)66.10±0.09°
Longitude of the node (Ω)60.48±0.14°
Periastron epoch (T)2454637.0±20.8
Argument of periastron (ω)
(secondary)		173.430±0.510°
Details
μ Her Aa
Mass1.134±0.007[9] M☉
Radius1.709+0.030
−0.015[12] R☉
Luminosity2.557±0.026[13] L☉
Surface gravity (log g)4.020±0.025[13] cgs
Temperature5,596±22[13] K
Metallicity [Fe/H]+0.26±0.04[13] dex
Rotation52+3
−1 d[8]
Rotational velocity (v sin i)1.7 ± 0.4[8] km/s
Age8.4+0.4
−0.1[12] Gyr
μ Her Ab
Mass0.2286±0.0006[9] M☉
μ Her B
Mass0.417±0.005[9] M☉
Radius0.378±0.026[14] R☉
Luminosity0.087[15] L☉
Temperature3,100±32[14] K
Metallicity [Fe/H]+0.40 dex
μ Her C[14]
Mass0.445±0.005[9] M☉
Radius0.378±0.026[14] R☉
Temperature3,100±32[14] K
Metallicity+0.40[14]
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.[16]
Database references
SIMBADμ Her Aab
μ Her BC

Mu Herculis (μ Herculis) is a nearby quadruple star system about 27.1 light years (8.3 parsecs) 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.[17] 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.[18]

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.[19] 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.[20][21] From this Chinese title, the name Kew Ho appeared.[22]

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.[23] The companion star is a red dwarf with a spectral type of M4±1V and a mass of 0.228 M☉.[5] This pair is also known as Mu1 Herculis.

The secondary component, also known as Mu2 Herculis,[24] consists of a pair of stars that orbit about each other with a period of about 43 years.[25] Mu Herculis A and the binary pair B-C are separated by some 35 arcseconds.[16] 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 0.179.[3]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 Cutri, R. M. (2003). "2MASS All-Sky Catalog of Point Sources". VizieR On-line Data Catalog 2246. Bibcode: 2003yCat.2246....0C. 
  3. ↑ 3.0 3.1 "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/wds/orb6. 
  4. ↑ Yang, Wuming; Meng, Xiangcun (April 2010). "Models of μ Her with asteroseismic constraints". New Astronomy 15 (4): 367–372. doi:10.1016/j.newast.2009.11.001. Bibcode: 2010NewA...15..367Y. 
  5. ↑ 5.0 5.1 Roberts Jr., Lewis C.; Mason, Brian D.; Aguilar, Jonathan et al. (2016-06-01). "Characterization of the Companion μ Her". The Astronomical Journal 151 (6): 169. doi:10.3847/0004-6256/151/6/169. ISSN 0004-6256. Bibcode: 2016AJ....151..169R. 
  6. ↑ 6.0 6.1 6.2 6.3 Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data: 0. Bibcode: 1986EgUBV........0M. http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1986EgUBV........0M&db_key=AST&nosetcookie=1. 
  7. ↑ Alonso-Floriano, F. J.; Morales, J. C.; Caballero, J. A. et al. (2015). "CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS". Astronomy & Astrophysics (EDP Sciences) 577: A128. doi:10.1051/0004-6361/201525803. ISSN 0004-6361. Bibcode: 2015A&A...577A.128A. https://www.aanda.org/articles/aa/full_html/2015/05/aa25803-15/aa25803-15.html. Retrieved 2026-04-16. 
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Grundahl, F.; Andersen, M. Fredslund; Christensen-Dalsgaard, J. et al. (2017-02-10). "First Results from the Hertzsprung SONG Telescope: Asteroseismology of the G5 Subgiant Star μ Herculis". The Astrophysical Journal 836 (1): 142. doi:10.3847/1538-4357/836/1/142. ISSN 0004-637X. Bibcode: 2017ApJ...836..142G. 
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 Marcussen, Marcus L.; Lund, Mikkel N.; Grundahl, Frank; et al. (2026-04-14). "The μ Herculis system solved after nearly three centuries". arXiv:2604.12492 [astro-ph.SR].
  10. ↑ 10.0 10.1 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. doi:10.1051/0004-6361:200809775. Bibcode: 2008A&A...488..401R. 
  11. ↑ Davison, Cassy L.; White, R. J.; Henry, T. J.; Riedel, A. R.; Jao, W. -C.; Bailey, J. I.; Quinn, S. N.; Cantrell, J. R. et al. (2015). "A 3D Search for Companions to 12 Nearby M Dwarfs". The Astronomical Journal 149 (3): 106. doi:10.1088/0004-6256/149/3/106. Bibcode: 2015AJ....149..106D. 
  12. ↑ 12.0 12.1 Gupta, Advik; Verma, Kuldeep; Kjeldsen, Hans et al. (2025-11-08). "Glitch analysis and asteroseismic modelling of subgiant μ Herculis: confirming and interpreting the Γ1 peak as the helium glitch". Monthly Notices of the Royal Astronomical Society (Oxford University Press (OUP)) 544 (4): 3428–3443. doi:10.1093/mnras/staf1953. ISSN 0035-8711. Bibcode: 2025MNRAS.544.3428G. 
  13. ↑ 13.0 13.1 13.2 13.3 Karovicova, I.; White, T. R.; Nordlander, T.; Casagrande, L.; Ireland, M.; Huber, D. (February 2022). "Fundamental stellar parameters of benchmark stars from CHARA interferometry -- III. Giant and subgiant stars". Astronomy & Astrophysics 658: A48. doi:10.1051/0004-6361/202142100. ISSN 0004-6361. Bibcode: 2022A&A...658A..48K. 
  14. ↑ 14.0 14.1 14.2 14.3 14.4 14.5 Houdebine, Éric R.; Mullan, D. J.; Doyle, J. G.; de la Vieuville, Geoffroy; Butler, C. J.; Paletou, F. (2019). "The Mass–Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs". The Astronomical Journal 158 (2): 56. doi:10.3847/1538-3881/ab23fe. Bibcode: 2019AJ....158...56H. 
  15. ↑ Gaidos, E.; Mann, A. W.; Lépine, S.; Buccino, A.; James, D.; Ansdell, M.; Petrucci, R.; Mauas, P. et al. (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. doi:10.1093/mnras/stu1313. Bibcode: 2014MNRAS.443.2561G. 
  16. ↑ 16.0 16.1 "* mu. Her". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+mu.+Her. 
  17. ↑ 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. http://www.astro.utoronto.ca/~garrison/mkstds.html. Retrieved 2012-02-04. 
  18. ↑ 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. doi:10.1093/mnras/55.8.429. Bibcode: 1895MNRAS..55..429K. 
  19. ↑ Script error: The function "in_lang" does not exist. 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.
  20. ↑ Script error: The function "in_lang" does not exist. AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 23 日
  21. ↑ Script error: The function "in_lang" does not exist. English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name , Hong Kong Space Museum. Accessed on line November 23, 2010.
  22. ↑ Star Name - R.H. Allen p. 238
  23. ↑ Debes, John H.; Ge, Jian; Chakraborty, Abhijit (2002-06-20). "First High-Contrast Imaging Using a Gaussian Aperture Pupil Mask". The Astrophysical Journal 572 (2): L165–L168. doi:10.1086/341876. Bibcode: 2002ApJ...572L.165D. https://iopscience.iop.org/article/10.1086/341876. Retrieved 2026-04-16. 
  24. ↑ "* mu.02 Her". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+mu.02+Her. 
  25. ↑ 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. doi:10.1086/321075. Bibcode: 2001AJ....121.3254T. 



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