Pi Scorpii

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Pi Scorpii
Diagram showing star positions and boundaries of the Scorpius constellation and its surroundings
Cercle rouge 100%.svg
Location of π Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 15h 58m 51.11324s[1]
Declination −26° 06′ 50.7886″[1]
Apparent magnitude (V) 2.890[2]
Spectral type B1 V + B2 V[3]
U−B color index −0.918[2]
B−V color index −0.187[2]
Variable type Eclipsing binary
Radial velocity (Rv)−3[4] km/s
Proper motion (μ) RA: −11.42[1] mas/yr
Dec.: −26.83[1] mas/yr
Parallax (π)5.57 ± 0.64[1] mas
Distanceapprox. 590 ly
(approx. 180 pc)
Absolute magnitude (MV)−3.35[5]
Period (P)1.570103 ± 0.000005 d[7]
Semi-major axis (a)~0.07 AU
Eccentricity (e)0.0
Inclination (i)~42°
Semi-amplitude (K1)
124.1 ± 1.5 km/s
Semi-amplitude (K2)
196.1 ± 1.8 km/s
π Sco A
Mass12.5 ± 0.6[8] M
Radius5[6] R
Luminosity21,900[9] L
Temperature25,230[9] K
Rotational velocity (v sin i)108[6] km/s
Age15.4 ± 0.6[8]
12–14[9] Myr
π Sco B
Radius4[6] R
Rotational velocity (v sin i)87[6] km/s
Other designations
Fang, 6 Scorpii, CD−25° 11228, HR 5944, HD 143018, HIP 78265, ADS 9862, SAO 183987, WDS 15589-2607
Database references

Pi Scorpii (π Scorpii, abbreviated Pi Sco, π Sco) is a triple star[10] system in the southern constellation of Scorpius. With a combined apparent magnitude of 2.9,[2] it can be easily seen with the naked eye. Parallax measurements yield an estimated distance of around 590 light-years (180 parsecs) from the Sun.[2]

It consists of a binary pair, designated Pi Scorpii A, with a more distant third companion, B. A's two components are themselves designated Pi Scorpii Aa (also named Fang[11]) and Ab.


π Scorpii (Latinised to Pi Scorpii) is the system's Bayer designation. The designations of the three constituents as Pi Scorpii A and B and those of A's components - Pi 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).[12]

In Chinese, 房宿 (Fáng Xiù), meaning Room, refers to an asterism consisting of Pi Scorpii, Rho Scorpii, Delta Scorpii, Beta¹ Scorpii and Beta² Scorpii.[13] Consequently, Pi Scorpii itself is known as 房宿一 (Fáng Xiù yī), "the First Star of Room".[14] In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[16] It approved the name Fang for the component Pi Scorpii Aa on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[11]


The fact that Pi Scorpii had two constituents (A and B) remained unknown until 1899, when it was announced by American astronomer Edward Charles Pickering. Two years later, an orbital period of 1.571 days was found by American astronomer Solon Irving Bailey, but it would not be until 1927 that the precise orbit of this spectroscopic binary was determined by Russian astronomer Otto Struve and American astrophysicist Christian T. Elvey.[6]

The primary, or A, component of this system itself forms an eclipsing binary of the Beta Lyrae type.[17] Both its members are hot, B-type main sequence stars with a blue-white hue. They display an ellipsoidal variation of 0.03 in magnitude.[7] The two stars are rotating rapidly, with projected rotational velocities of 108 and 87 km/s respectively.[6] Their orbital period is 1.57 days and they are separated by an estimated distance of only 15 solar radii along a circular orbit.[6]

The primary is orbited by a smaller, more distant companion (B), which has an apparent magnitude of +12.2. This component is separated from the pair by 50 arcseconds, putting it at least 7000 AU away.[citation needed]

The Pi Scorpii system is a kinematic member of the Upper Scorpius subgroup of the Scorpius-Centaurus Association, a group of thousands of young stars with mean age 11 million years at distance 470 light years (145 parsecs).[9] A recent analysis[9] of the HR diagram position for the primary star Pi Scorpii A estimates its effective temperature to be 25,230 kelvins with a luminosity of 21,900 Suns, consistent with an isochronal age of 12-14 million years and an estimated mass of 12–13 solar masses.


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d e 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. ^ Houk, Nancy; Smith-Moore, M. (1979), "Michigan catalogue of two-dimensional spectral types for the HD stars", Ann Arbor : Dept. of Astronomy, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, 1, Bibcode:1978mcts.book.....H 
  4. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E 
  5. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971Freely accessible, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015. 
  6. ^ a b c d e f g h Stickland, D. J.; et al. (December 1996), "Spectroscopic binary orbits from ultraviolet radial velocities Paper 23: Pi Scorpii (HD 143018)", The Observatory, 116: 387–391, Bibcode:1996Obs...116..387S 
  7. ^ a b Shobbrook, R. R. (December 2005), "Photometry of 20 eclipsing and ellipsoidal binary systems", The Journal of Astronomical Data, 11: 1–17, Bibcode:2005JAD....11....7S 
  8. ^ a b Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  9. ^ a b c d e f Mark J. Pecaut; Eric E. Mamajek & Eric J. Bubar (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association". Astrophysical Journal. 746 (2): 154. arXiv:1112.1695Freely accessible. Bibcode:2012ApJ...746..154P. doi:10.1088/0004-637X/746/2/154. 
  10. ^ Kaler, James B., "PI SCO (Pi Scorpii)", Stars, University of Illinois, retrieved 2012-01-14 
  11. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017. 
  12. ^ 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:1012.0707Freely accessible [astro-ph.SR]. 
  13. ^ (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.
  14. ^ (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.
  15. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  16. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14. 
  17. ^ "pi. Sco -- Eclipsing binary of beta Lyr type", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-14