Epsilon Scorpii

Epsilon Scorpii (ε Scorpii, abbreviated Eps Sco, ε Sco), formally named Larawag /ˈlærəwæɡ/,[12] is a star in the southern zodiac constellation of Scorpius. It has an apparent visual magnitude of +2.3,[2] making it the fifth-brightest member of the constellation. Parallax measurements made during the Hipparcos mission provide an estimated distance to this star of around 63.7 light-years (19.5 parsecs) from the Sun.[1]

ε Scorpii
Location of ε Sco (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 16h 50m 09.8s[1]
Declination –34° 17′ 36″[1]
Apparent magnitude (V) +2.310[2] (2.24 - 2.35)[3])
Characteristics
Spectral type K1 III[4]
U−B color index +1.147[2]
B−V color index +1.150[2]
Variable type suspected[3]
Astrometry
Radial velocity (Rv)–2.5[5] km/s
Proper motion (μ) RA: –614.85[1] mas/yr
Dec.: –255.98[1] mas/yr
Parallax (π)51.19 ± 0.22[1] mas
Distance63.7 ± 0.3 ly
(19.54 ± 0.08 pc)
Absolute magnitude (MV)0.78 ± 0.04[6]
Details
Mass1.24[7] M☉
Radius12.6[8] R☉
Surface gravity (log g)2.49[9] cgs
Temperature4,560[9] K
Metallicity [Fe/H]–0.17[9] dex
Rotational velocity (v sin i)2.6 ± 0.5[10] km/s
Other designations
Wei, Larawag, 26 Scorpii, CD–34 11285, FK5 628, GCTP 3823.00, Gl 639.1, HD 151680, HIP 82396, HR 6241, LHS 3244, SAO 208078.[11]
Database references
SIMBADdata

Epsilon Scorpii has a stellar classification of K1 III,[4] which indicates it has exhausted the supply of hydrogen at its core and evolved into a giant star. The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 5.99 ± 0.06 mas,[13] which, at its estimated distance, equates to a physical radius of nearly 13 times the radius of the Sun.[8] Presently it is generating energy through the nuclear fusion of helium at its core, which, considering the star's composition, places it along an evolutionary branch termed the red clump.[14] The star's outer atmosphere has an effective temperature of 4,560 K,[9] giving it the orange hue of a cool K-type star.

ε Scorpii is classified as a suspected variable star,[3] although a study of Hipparcos photometry showed a variation of no more than 0.01–0.02 magnitudes.[14] It is an X-ray source with a luminosity of (1.5–1.6) × 1027 erg s−1.[6][15]

Nomenclature

ε Scorpii (Latinised to Epsilon Scorpii) is the star's Bayer designation.

The star bore the traditional name Larawag in the culture of the Wardaman people of the Northern territory of Australia,[16] meaning clear sighting.[17] In 2016, the IAU organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN approved the name Larawag for Epsilon Scorpii on 19 November 2017 and it is now so included in the List of IAU-approved Star Names.[12]

Patrick Moore introduced the name Wei as Chinese name for this star.[19] However, this seems to be a misreading, as Chinese 尾宿 (Wěi Xiù, English Tail) refers to an asterism (i.e. Chinese constellation) consisting of Epsilon Scorpii, Mu¹ Scorpii, Zeta¹ Scorpii and Zeta² Scorpii, Eta Scorpii, Theta Scorpii, Iota² Scorpii and Iota¹ Scorpii, Kappa Scorpii, Lambda Scorpii and Upsilon Scorpii.[20] Consequently, the name for Epsilon Scorpii itself is 尾宿二 (Wěi Xiù èr), which means "the Second Star of Tail".[21][22]

In culture

Epsilon Scorpii appears on the flag of Brazil, symbolising the state of Ceará.[23]

See also: Epsilon Scorpii in fiction

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. 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. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.
  4. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992
  5. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W
  6. Schroeder, K.-P.; Huensch, M.; Schmitt, J. H. M. M. (July 1988), "X-ray activity and evolutionary status of late-type giants", Astronomy and Astrophysics, 335: 591–595, Bibcode:1998A&A...335..591S
  7. Fuhrmann, K; Chini, R; Kaderhandt, L; Chen, Z (2017). "Multiplicity among Solar-type Stars". The Astrophysical Journal. 836 (1): 139. Bibcode:2017ApJ...836..139F. doi:10.3847/1538-4357/836/1/139.
  8. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  9. McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527
  10. Carney, Bruce W.; et al. (March 2008), "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars", The Astronomical Journal, 135 (3): 892–906, arXiv:0711.4984, Bibcode:2008AJ....135..892C, doi:10.1088/0004-6256/135/3/892, S2CID 2756572
  11. "eps Sco". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-02-23.
  12. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  13. Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039
  14. Adelman, Saul J. (2001), "On the Photometric Variability of Red Clump Giants", Baltic Astronomy, 10 (4): 593–597, Bibcode:2001BaltA..10..593A, doi:10.1515/astro-2001-0404
  15. Gondoin, P. (December 1999), "Evolution of X-ray activity and rotation on G-K giants", Astronomy and Astrophysics, 352: 217–227, Bibcode:1999A&A...352..217G
  16. "IAU Approves 86 New Star Names From Around the World" (Press release). IAU.org. 11 December 2017.
  17. "IAU Working Group on Star Names (WGSN)" (Press release). IAU.org.
  18. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  19. Moore, P. (1983), The Guinness Book of Astronomy: Facts (2nd ed.), Middlesex, UK: Guinness Superlatives Limited, p. 242
  20. (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.
  21. (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.
  22. Ridpath, Ian, Star Tales.
  23. "Astronomy of the Brazilian Flag". FOTW Flags Of The World website.
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