Theta Scorpii

Theta Scorpii (θ Scorpii, abbreviated Theta Sco, θ Sco) is a binary star in the southern zodiac constellation of Scorpius. The apparent visual magnitude of this star is +1.87,^[5] making it readily visible to the naked eye and one of the brightest stars in the night sky. It is sufficiently near that the distance can be measured directly using the parallax technique and such measurements obtained during the Hipparcos mission yield an estimate of approximately 329 light-years (101 parsecs) from the Sun.

Theta Scorpii

Location of θ Scorpii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius
Right ascension	17h 37m 19.12985s[1]
Declination	−42° 59′ 52.1808″[1]
Apparent magnitude (V)	1.84 (1.862 + 6.22)[2]
Characteristics
Spectral type	F0Ib-F1III[3] or F0 II[4]
U−B color index	+0.21[5]
B−V color index	+0.40[5]
Astrometry
Radial velocity (Rv)	+1.4[6] km/s
Proper motion (μ)	RA: +5.54[1] mas/yr Dec.: −3.12[1] mas/yr
Parallax (π)	9.90 ± 0.26 mas[7]
Distance	329 ± 9 ly (101 ± 3 pc)
Absolute magnitude (MV)	−2.71[8]
Details
Mass	3.10+0.37 −0.32[7] M☉
Radius	26.3 - 35.5[7] R☉
Luminosity	1,400[7] L☉
Surface gravity (log g)	2.4±0.2[9] cgs
Temperature	6,294[7] K
Rotation	16.60[7] d
Rotational velocity (v sin i)	125[10] km/s
Other designations
Sargas, Girtab, 160 G. Scorpii, θ Sco, CD−42°12312, FK5 654, HD 159532, HIP 86228, HR 6553, SAO 228201, CCDM J17373−4300[11]
Database references
SIMBAD	data

The two components are designated θ Scorpii A (officially named Sargas /ˈsɑːrɡæs/, the traditional name for the system)^[12][13] and B.

Nomenclature

θ Scorpii (Latinised to Theta Scorpii) is the system's Bayer designation. The designations of the two components as Theta Scorpii A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).^[14]

It bore the traditional name Sargas, of Sumerian origin.^[15] Another possible origin is Persian for Arrow Head سر گز. The name 'Sar Gaz' is used in Iran as a star name, and was used for timing irrigation water shares.^[16] In 2016, the IAU organized a Working Group on Star Names (WGSN)^[17] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.^[18] It approved the name Sargas for the star θ Scorpii A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.^[13]

In Chinese, 尾宿 (Wěi Xiù), meaning Tail, refers to an asterism consisting of Theta Scorpii, Epsilon Scorpii, Zeta¹ Scorpii and Zeta² Scorpii, Eta Scorpii, Iota¹ Scorpii and Iota² Scorpii, Kappa Scorpii, Lambda Scorpii, Mu¹ Scorpii and Upsilon Scorpii.^[19] Consequently, the Chinese name for Theta Scorpii itself is 尾宿五 (Wěi Xiù wǔ), "the Fifth Star of Tail".^[20]

Properties

The primary (θ Scorpii A) is an evolved bright giant star with a stellar classification of F0 II.^[4] With a mass 3.10 times that of the Sun, it is radiating 1,400^[7] times as much luminosity as the Sun from its outer envelope at an effective temperature of 6,294 K,^[7] giving it the yellow-white-hued glow of an F-type star. This star is rotating rapidly, giving it an oblate shape with an equatorial radius 33% larger than the polar radius. The equatorial radius is about 36 R_☉ while the polar radius is only about 26 R_☉. This rapid rotation suggests that it formed via the merger of a binary star system.^[7]

A magnitude 5.36 companion has been reported at an angular separation of 6.470 arcseconds,^[21] but subsequent observers have failed to detect it, so it probably does not exist. However, a secondary, designated θ Scorpii B, has been detected at an angular separation of 0.538 arcseconds in 1991 by the Hipparcos satellite.^[7]

Modern legacy

Theta Scorpii appears on the flag of Brazil, symbolising the state of Alagoas.^[22]

References

1. 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. S2CID 18759600.
2. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862.
3. Ayres, Thomas R. (2018-02-20). "Cracking the Conundrum of F-Supergiant Coronae". The Astrophysical Journal. 854 (2): 95. arXiv:1802.02552. Bibcode:2018ApJ...854...95A. doi:10.3847/1538-4357/aaa6d7. ISSN 0004-637X.
4. Houk, Nancy (1978). "Michigan catalogue of two-dimensional spectral types for the HD stars". Ann Arbor: Dept. Of Astronomy. 2. Ann Arbor: Departement of Astronomy, University of Michigan. Bibcode:1978mcts.book.....H.
5. Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
6. Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Carnegie Institute of Washington D.C. Bibcode:1953GCRV..C......0W.
7. Lewis, Fiona; Bailey, Jeremy; Cotton, Daniel V.; Howarth, Ian D.; Kedziora-Chudczer, Lucyna; Van Leeuwen, Floor (2022). "A study of the F-giant star θ Scorpii A: A post-merger rapid rotator?". Monthly Notices of the Royal Astronomical Society. 513 (1): 1129–1140. arXiv:2204.02719. Bibcode:2022MNRAS.513.1129L. doi:10.1093/mnras/stac991.
8. 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. S2CID 119257644.
9. Samedov, Z. A. (1988). "Investigation of the atmospheres of the stars ι1 Sco (F2 Ia) and θ Sco (F1 II)". Astrophysics. 28 (3): 335–341. Bibcode:1988Ap.....28..335S. doi:10.1007/BF01112969. S2CID 119828317.
10. van Belle, Gerard T. (March 2012). "Interferometric observations of rapidly rotating stars". The Astronomy and Astrophysics Review. 20 (1): 51. arXiv:1204.2572. Bibcode:2012A&ARv..20...51V. doi:10.1007/s00159-012-0051-2. S2CID 119273474.
11. "* tet Sco". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-02-18.
12. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
13. "Naming Stars". IAU.org. Retrieved 3 March 2018.
14. 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].
15. Burnham, Robert (1978). Burnham's celestial handbook: an observer's guide to the universe beyond the solar system. Dover books explaining science. Vol. 3 (2nd ed.). Courier Dover Publications. p. 1676. ISBN 0-486-23673-0.
16. Nash, Harriet; et al. (2012). Traditional Timing of Qanat Water Shares. International Conference on Traditional Knowledge for Water. Retrieved 26 April 2017.
17. "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Retrieved 22 May 2016.
18. "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
19. (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.
20. (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.
21. Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
22. "Astronomy of the Brazilian Flag". Flags of the World.

External links

• Theta Sco