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 (formally named Fang)[11] and Ab.
Nomenclature
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, the Chinese name for Pi Scorpii itself is 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 primary, or A, component of this system itself forms an eclipsing binary of the Beta Lyrae type.[17] Both its members are hot, B-typemain 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.
^ abcdeGutierrez-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
^Houk, Nancy; Smith-Moore, M. (1979), "Michigan catalogue of two-dimensional spectral types for the HD stars", Ann Arbor: Dept. Of Astronomy, 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H
^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, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E
^ abcdefghStickland, 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
^ abcShobbrook, R. R. (December 2005), "Photometry of 20 eclipsing and ellipsoidal binary systems", The Journal of Astronomical Data, 11: 7, Bibcode:2005JAD....11....7S
^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].
^(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, ISBN978-986-7332-25-7.
