Mu¹ Scorpii (μ¹ Scorpii, abbreviated Mu¹ Sco, μ¹ Sco) is a binary star system in the southern zodiac constellation of Scorpius. The combined apparent visual magnitude of the pair is +3.04,[2] making it one of the brighter members of Scorpius. Based upon parallax measurements, the distance of this system from the Sun is roughly 500 light-years (150 parsecs).[1] This system is a member of the Scorpius–Centaurus Association, the nearest OB association of co-moving stars to the Sun.[3]

μ¹ Scorpii
Scorpius constellation map.svg
Red circle.svg
Location of μ¹ Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension  16h 51m 52.23111s[1]
Declination −38° 02′ 50.5694″[1]
Apparent magnitude (V) +3.04[2]
Spectral type B1.5 V + B6.5 V[3]
U−B color index –0.859[2]
B−V color index –0.202[2]
Radial velocity (Rv)–25[4] km/s
Proper motion (μ) RA: –10.58[1] mas/yr
Dec.: –22.06[1] mas/yr
Parallax (π)6.51 ± 0.91[1] mas
Distanceapprox. 500 ly
(approx. 150 pc)
Absolute magnitude (MV)–2.9 ± 0.3[3]
Period (P)1.44627 days
Semi-major axis (a)12.90 ± 0.04 R
Eccentricity (e)0.0
Inclination (i)65.4 ± 1°
Periastron epoch (T)2412374.434 HJD
μ1 Sco A
Mass8.49 ± 0.05[3] M
Radius4.07 ± 0.05[3] R
Temperature23,725 ± 500[3] K
μ¹ Sco B
Mass5.33 ± 0.05[3] M
Radius4.38 ± 0.05[3] R
Temperature16,850 ± 500[3] K
Other designations
Xamidimura, CD−37°11033, FK5 1439, HD 151890, HIP 82514, HR 6247, SAO 208102, Washington Double Star Catalog 16519-3803
Database references
For other star systems with a similar Bayer designation, see Mu Scorpii.

The primary (Mu¹ Scorpii Aa) is formally named Xamidimura /ˌkæmidiˈmʊərə/, from the Khoekhoe xami di mûra IPA: [xami ti mũːɾa] 'the (two) eyes of the lion'.[5]


Mu¹ Scorpii is an eclipsing binary of the Beta Lyrae type. Discovered to be a spectroscopic binary by Solon Irving Bailey in 1896, it was only the third such eclipsing pair to be discovered. This is a semidetached binary system where the secondary is close to filling its Roche lobe, or it may even be overflowing. The two stars revolve each other along a circular orbit with the components separated by 12.9 times the Sun's radius.[3] Due to occultation of each component by the other, the apparent magnitude of the system decreased by 0.3 and 0.4 magnitudes over the course of the binary's orbit, which takes 34 hours 42.6 minutes to complete.

The primary component is a B-type main sequence star with a stellar classification of B1.5 V. It has 8.5 times the mass of the Sun and 4.1 times the Sun's radius. The secondary is a smaller B-type main sequence star with a classification of about B6.5 V, having 5.3 times the Sun's mass and 4.4 times the radius of the Sun. The effective temperature of the outer atmosphere for each star is 23,725 K for the primary and 16,850 K for the secondary.[3] At these temperatures, the two stars glow with a blue-white hue.[6]


μ¹ Scorpii (Latinised to Mu¹ Scorpii) is the system's Bayer designation. The designations of the primary as Mu¹ Scorpii Aa derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[7]

The pair of stars Mu¹ and Mu² Scorpii are known as the xami di mura 'eyes of the lion' by the Khoikhoi people of South Africa.[8]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[9] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[10] It approved the name Xamidimura for the component Mu¹ Scorpii Aa on 5 September 2017 (along with Pipirima for the partner of Mu¹ Scorpii) and it is now so included in the List of IAU-approved Star Names.[5]

In Chinese, 尾宿 (Wěi Xiù), meaning Tail, refers to an asterism consisting of Mu¹ Scorpii, Epsilon Scorpii, Zeta¹ Scorpii and Zeta² Scorpii, Eta Scorpii, Theta Scorpii, Iota¹ Scorpii and Iota² Scorpii, Kappa Scorpii, Lambda Scorpii and Upsilon Scorpii.[11] Consequently, the Chinese name for Mu¹ Scorpii itself is 尾宿一 (Wěi Xiù yī), "the First Star of Tail".[12]


  1. ^ 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
  2. ^ a b c d Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement, 15: 459, Bibcode:1968ApJS...15..459G, doi:10.1086/190168
  3. ^ a b c d e f g h i j k l van Antwerpen, C.; Moon, T. (January 2010), "New observations and analysis of the bright semidetached eclipsing binary μ1 Sco", Monthly Notices of the Royal Astronomical Society, 401 (3): 2059–2066, arXiv:0910.1241, Bibcode:2010MNRAS.401.2059V, doi:10.1111/j.1365-2966.2009.15796.x
  4. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W
  5. ^ a b "Naming Stars". Retrieved 16 December 2017.
  6. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
  7. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  8. ^ Astronomical Society of Southern Africa (2013) African ethnoastronomy
  9. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  10. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  11. ^ (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.
  12. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.