Astronomy:Sigma Sagittarii

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Short description: Second brightest star in the constellation Sagittarius
Sigma Sagittarii
Sagittarius IAU.svg
Red circle.svg
Location of σ Sagittarii (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Sagittarius
Right ascension  18h 55m 15.92650s[1][2]
Declination –26° 17′ 48.2068″[1][2]
Apparent magnitude (V) 2.05[3]
Characteristics
Spectral type B2.5 V[4]
U−B color index –0.761[5]
B−V color index –0.204[5]
Astrometry
Radial velocity (Rv)–11.2[3] km/s
Proper motion (μ) RA: +15.14[1][2] mas/yr
Dec.: –53.43[1][2] mas/yr
Parallax (π)14.32 ± 0.29[1][2] mas
Distance228 ± 5 ly
(70 ± 1 pc)
Absolute magnitude (MV)−2.17[6]
Details
Mass7.8±0.2[7] M☉
Radius4.5[8] R☉
Luminosity3,300[9] L☉
Temperature18,890[9] K
Rotational velocity (v sin i)165[10] km/s
Age31.4±0.4[7] Myr
Other designations
Database references
SIMBADdata

Sigma Sagittarii, Latinized from σ Sagittarii; formally named Nunki /ˈnʌŋki/,[11][12] is the second-brightest star in the constellation of Sagittarius. It has an apparent magnitude of +2.05,[3] making it readily visible to the naked eye. The distance to this star, determined using parallax measurements from the Hipparcos astrometry satellite,[13] yields a value of approximately 228 light-years (70 parsecs) from the Sun.[1][2]

Properties

Sigma Sagittarii has a spectrum matching a stellar classification of B2.5 V,[4] which indicates this is a B-type main-sequence star. Its total luminosity is 3300[14] times that of the Sun while it has a surface temperature of 18,890 K.[9] X-ray emission has been detected from this star, which has an estimated X-ray luminosity of 1.2 × 1028 erg s−1.[15]

It has a 10th magnitude optical companion located 5.2 arcminutes away.[16]

It is 3.45 degrees south of the ecliptic, so it can be occulted by the Moon and rarely by planets. The last occultation by a planet took place on November 17, 1981, when it was occulted by Venus.[17] This is the brightest star that can be principally occulted by an exterior planet between 5000 BC and 5000 AD. However, only Mars can do this, and only rarely; the last time was on September 3, 423.[citation needed]

Nomenclature

σ Sagittarii (Latinised to Sigma Sagittarii) is the star's Bayer designation. In his Uranometria star atlas, Johann Bayer placed this star in the fourth magnitude class, although it is a second-magnitude star by modern measurements.[citation needed]

It bore the traditional name of Nunki, which was an Assyrian or Babylonian name recovered by archaeologists and made public by R. H. Allen.[18] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[19] to catalogue and standardize proper names for stars. The WGSN approved the name Nunki for this star on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[12]

This star, together with :

Zeta Sagittarii and Pi Sagittarii may have been the Akkadian Gu-shi-rab‑ba, the Yoke of the Sea.[21]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Thanih al Sadirah, which was translated into Latin as Secunda τού al Sadirah, meaning second returning ostrich.[22]

In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of Sigma Sagittarii, Phi Sagittarii, Lambda Sagittarii, Mu Sagittarii, Tau Sagittarii and Zeta Sagittarii. Consequently, the Chinese name for Sigma Sagittarii itself is 斗宿四 (Dǒu Xiù sì, English: the Fourth Star of Dipper.)[23]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; Bastian, U.; Bernacca, P. L.; Crézé, M.; Donati, F. et al. (July 1997), "The Hipparcos Catalogue", Astronomy and Astrophysics 323: L49–L52, Bibcode: 1997A&A...323L..49P 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Van Leeuwen, Floor (2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  3. ↑ 3.0 3.1 3.2 Wielen, R. et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode: 1999VeARI..35....1W 
  4. ↑ 4.0 4.1 Houk, Nancy (1979), "Michigan catalogue of two-dimensional spectral types for the HD stars", Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume_3. Declinations -40_ƒ0 to -26_ƒ0 (Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan) 3, Bibcode: 1982mcts.book.....H 
  5. ↑ 5.0 5.1 Gutierrez-Moreno, Adelina; Moreno, Hugo (June 1968), "A photometric investigation of the Scorpio-Centaurus association", Astrophysical Journal Supplement 15: 459, doi:10.1086/190168, Bibcode: 1968ApJS...15..459G 
  6. ↑ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A. 
  7. ↑ 7.0 7.1 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, doi:10.1111/j.1365-2966.2010.17434.x, Bibcode: 2011MNRAS.410..190T 
  8. ↑ Underhill, A. B. et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society 189 (3): 601–605, doi:10.1093/mnras/189.3.601, Bibcode: 1979MNRAS.189..601U 
  9. ↑ 9.0 9.1 9.2 Zorec, J. et al. (July 2009), "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff", Astronomy and Astrophysics 501 (1): 297–320, doi:10.1051/0004-6361/200811147, Bibcode: 2009A&A...501..297Z 
  10. ↑ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, doi:10.1086/340590, Bibcode: 2002ApJ...573..359A 
  11. ↑ Davis, George A. (1944). "The pronunciations, derivations, and meanings of a selected list of star names". Popular Astronomy 52: 26. Bibcode: 1944PA.....52....8D. http://adsbit.harvard.edu/full/1944PA.....52....8D. 
  12. ↑ 12.0 12.1 "Naming Stars". IAU.org. https://www.iau.org/public/themes/naming_stars/. 
  13. ↑ Perryman, Michael (2010), The Making of History's Greatest Star Map, Astronomers’ Universe, Heidelberg: Springer-Verlag, doi:10.1007/978-3-642-11602-5, ISBN 978-3-642-11601-8, Bibcode: 2010mhgs.book.....P, https://cds.cern.ch/record/1338896 
  14. ↑ James B. Kaler, "NUNKI (Sigma Sagatarii)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/nunki.html, retrieved 2012-01-31 
  15. ↑ Cassinelli, J. P. et al. (February 1994), "X-ray emission from near-main-sequence B stars", Astrophysical Journal, Part 1 421 (2): 705–717, doi:10.1086/173683, Bibcode: 1994ApJ...421..705C 
  16. ↑ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M. 
  17. ↑ Können, G. P.; Van Maanen, J. (April 1981). "Planetary occultations of bright stars.". Journal of the British Astronomical Association 91: 148–157. Bibcode: 1981JBAA...91..148K. 
  18. ↑ Allen, Richard Hinckley, Star Names, their lore and meaning, p. 359 
  19. ↑ IAU Working Group on Star Names (WGSN), International Astronomical Union, https://www.iau.org/science/scientific_bodies/working_groups/280/, retrieved 22 May 2016. 
  20. ↑ "Teapot". constellation-guide.com. http://www.constellation-guide.com/teapot/. 
  21. ↑ 21.0 21.1 Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc.. p. 355. ISBN 0-486-21079-0. https://archive.org/details/starnamestheirlo00alle/page/355. Retrieved 2012-09-04. 
  22. ↑ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55 (8): 430. doi:10.1093/mnras/55.8.429. Bibcode: 1895MNRAS..55..429K. 
  23. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日

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