Rho Scorpii

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ρ Scorpii
Scorpius constellation map.svg
Red circle.svg
Location of ρ Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension  15h 56m 53.07624s[1]
Declination −29° 12′ 50.6612″ [1]
Apparent magnitude (V) 3.86[2]
Spectral type B2 IV[3]
U−B color index -0.82[2]
B−V color index -0.20[2]
Radial velocity (Rv)−0.40[4] km/s
Proper motion (μ) RA: −15.68[1] mas/yr
Dec.: −24.88[1] mas/yr
Parallax (π)6.91 ± 0.19[1] mas
Distance470 ± 10 ly
(145 ± 4 pc)
Absolute magnitude (MV)−1.93[5]
Period (P)4.0033 d
Eccentricity (e)0.27
Periastron epoch (T)2442178.6060 JD
Argument of periastron (ω)
Semi-amplitude (K1)
16.40 km/s
Mass7.94±0.55[3] M
Radius5.0[7] R
Luminosity (bolometric)3,432[3] L
Temperature21,150[3] K
Rotational velocity (v sin i)113[8] km/s
Other designations
Iklil, 5 Scorpii, ADS 9846, CCDM J15569-2913A, FK5 3258, GC 21398, HD 142669, HIP 78104, HR 5928, SAO 183957, CD−28° 11714[9]
Database references

Rho Scorpii (ρ Scorpii, abbreviated Rho Sco, ρ Sco) is a double star in the constellation of Scorpius. It has an apparent visual magnitude of +3.87, which is bright enough to be seen with the naked eye. Based upon parallax measurements, it is located approximately 472 light years from the Sun.[1] At that distance, the visual magnitude of the system is reduced by 0.07 due to extinction from interstellar dust.[10] It is a member of the Upper Scorpius OB association.[11]

It has two components, designated Rho Scorpii A and B. Rho Scorpii A is itself a single-lined spectroscopic binary whose components are designated Rho Scorpii Aa (formally named Iklil /ˈɪklɪl/, traditionally the name for several neighboring stars)[12] and Ab.


ρ Scorpii (Latinised to Rho Scorpii) is the system's Bayer designation. The designations of the three constituents as Rho Scorpii A and B, and those of A's components - Rho Scorpii Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[13]

Rho Scorpii was likely part of the Arabic lunar mansion of Iklil (الإكليل al-ʼiklīl) "the crown (of the forehead)"), along with Beta, Delta, Pi and possibly Nu Scorpii.

The corresponding asterism in Chinese astronomy, 房宿 (Fáng Xiù), meaning Room, consists of Rho Scorpii, Pi Scorpii, Delta Scorpii, Beta¹ Scorpii and Beta² Scorpii.[14] Consequently, the Chinese name for ρ Scorpii itself is 房宿二 (Fáng Xiù èr), "the Second Star of Room".[15]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[17] It approved the name Iklil for the component Rho Scorpii Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[12]


Rho Scorpii A displays the spectrum of blue-white B-type subgiant with a stellar classification of B2 IV.[3] It has an estimated mass nearly 8 times that of the Sun's and shines with 3,432 times the Sun's luminosity.[3] The two constituent stars orbit each other with a period of 4 days and an eccentricity of 0.27.[6]

Rho Scorpii B is a magnitude 12.80 visual companion that lies at an angular separation of 38.40 arcseconds along a position angle of 95°, as of the year 2000.[18]


  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 Ducati, J. R. (2002), "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system", CDS/ADC Collection of Electronic Catalogues, 2237, Bibcode:2002yCat.2237....0D.
  3. ^ a b c d e f Hohle, M. M.; et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
  4. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick (eds.), Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E.
  5. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  6. ^ a b Pourbaix, D.; et al. (September 2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424: 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  7. ^ Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics, 367 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  8. ^ Simón-Díaz, S.; Herrero, A. (2014), "The IACOB project: I. Rotational velocities in northern Galactic O- and early B-type stars revisited. The impact of other sources of line-broadening", Astronomy & Astrophysics, 562: A135, arXiv:1311.3360, Bibcode:2014A&A...562A.135S, doi:10.1051/0004-6361/201322758.
  9. ^ "rho Sco". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-09-22.
  10. ^ Shatsky, N.; Tokovinin, A. (January 2002), "The mass ratio distribution of B-type visual binaries in the Sco OB2 association", Astronomy and Astrophysics, 382: 92–103, arXiv:astro-ph/0109456, Bibcode:2002A&A...382...92S, doi:10.1051/0004-6361:20011542.
  11. ^ Grellmann, R.; et al. (June 2015), "New constraints on the multiplicity of massive young stars in Upper Scorpius", Astronomy & Astrophysics, 578: 11, Bibcode:2015A&A...578A..84G, doi:10.1051/0004-6361/201219577, A84.
  12. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  13. ^ 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].
  14. ^ (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.
  15. ^ (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.
  16. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  17. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  18. ^ Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920

External links[edit]

  • Kaler, James B. (June 20, 2008), "Rho Scorpii", Stars, University of Illinois, retrieved 2016-09-23.