Lambda Sagittarii

Lambda Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings


Location of λ Sagittarii (circled)

Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension 18h 27m 58.24072s[1]
Declination −25° 25′ 18.1146″[1]
Apparent magnitude (V) +2.82[2]
Characteristics
Spectral type K0 IV[3]
U−B color index +0.903[4]
B−V color index +1.045[4]
Astrometry
Radial velocity (Rv)−43.5[2] km/s
Proper motion (μ) RA: −44.76[1] mas/yr
Dec.: −185.66[1] mas/yr
Parallax (π)41.72 ± 0.16[1] mas
Distance78.2 ± 0.3 ly
(23.97 ± 0.09 pc)
Details
Mass2.6[5] M☉
Radius11[6] R☉
Surface gravity (log g)2.90[7] cgs
Temperature4,770[7] K
Metallicity [Fe/H]–0.20[8] dex
Rotational velocity (v sin i)3.81[7] km/s
Other designations
Kaus Borealis, λ Sagittarii, λ Sgr, Lambda Sgr, 22 Sagittarii, CPD-25  6523, FK5 692, GC 25180, HD 169916, HIP 90496, HR 6913, PPM 268438, SAO 186841.

Lambda Sagittarii (λ Sagittarii, abbreviated Lambda Sgr, λ Sgr), also named Kaus Borealis,[9] is a star within the southern constellation of Sagittarius. The star marks the top of the Archer's bow.

Properties

With an apparent visual magnitude of +2.82,[2] this is one of the brighter members of the constellation and, accordingly to the Bortle Dark-Sky Scale, it is readily visible to the naked eye. Based upon parallax measurements, it is located at a distance of 78.2 light-years (24.0 parsecs) from the Sun.[1] Being near the ecliptic, Lambda Sgr is sometimes occulted by the Moon and, more rarely, by a planet. The last planet to pass in front of it was Venus, on 19 November 1984. The previous occasion was on 5 December 1865, when it was occulted by the planet Mercury.

Kaus Borealis is a subgiant star with a stellar classification of K0 IV.[3] It has a mass 2.6 times that of the Sun.[5] The interferometry-measured angular diameter of this star, after correction for limb darkening, is 4.24 ± 0.05 mas.[10] At the estimated distance of Lambda Sagittarii,[1] this yields a physical size of about 11 times the radius of the Sun.[6] This expanded outer envelope is radiating energy at an effective temperature of 4,770 K,[7] causing it to glow with the cool orange hue of a K-type star.[11] It appears to be rotating at a leisurely rate, with a projected rotational velocity of 3.81 km s−1.[7]

Nomenclature

λ Sagittarii (Latinised to Lambda Sagittarii) is the star's Bayer designation.

It bore the traditional name Kaus Borealis, which derives from the Arabic قوس qaws 'bow' and Latin boreālis 'northern'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[13] included a table of the first two batches of names approved by the WGSN; which included Borealis for this star.

This star, together with Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii, Zeta Sagittarii, Sigma Sagittarii, Tau Sagittarii and Phi Sagittarii comprises the asterism 'Teapot'.[14][15]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Rai al Naaim, which was translated into Latin as Pastor Struthionum, meaning keeper of the ostriches.[16]

This star is Al Tizini's Rāʽi al Naʽāïm (ألراع ٱلنعم), the Keeper of the Naʽams (Ostrich), meaning the "keeper" the two asterisms Al Naʽām al Wārid (النعم الوارد), "The Going Ostriches" and Al Naʽām al Ṣādirah (النعم السادرة), "The Returning Ostriches".[17]

In Chinese, 斗 (Dǒu), meaning Dipper, refers to an asterism consisting of Lambda Sagittarii, Phi Sagittarii, Mu Sagittarii, Sigma Sagittarii, Tau Sagittarii and Zeta Sagittarii. Consequently, Lambda Sagittarii itself is known as 斗宿二 (Dǒu Sù èr, English: the Second Star of Dipper.)[18]

References

  1. 1 2 3 4 5 6 7 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. 1 2 3 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.
  3. 1 2 Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770Freely accessible, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
  4. 1 2 Gutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards", Publ. Dept. Astron. Univ. Chile, Publicaciones Universidad de Chile, Department de Astronomy, 1: 1–17, Bibcode:1966PDAUC...1....1G.
  5. 1 2 Edvardsson, B. (January 1988), "Spectroscopic surface gravities and chemical compositions for 8 nearby single sub-giants", Astronomy and Astrophysics, 190 (1–2): 148–166, Bibcode:1988A&A...190..148E.
  6. 1 2 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3 ed.), Birkhäuser, ISBN 3540296921. The radius (R*) is given by:
  7. 1 2 3 4 5 Hekker, S.; Meléndez, J. (2007), "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters", Astronomy and Astrophysics, 475 (3): 1003–1009, arXiv:0709.1145Freely accessible, Bibcode:2007A&A...475.1003H, doi:10.1051/0004-6361:20078233.
  8. ↑ McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series, 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527.
  9. ↑ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  10. ↑ 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.
  11. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16.
  12. ↑ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  13. ↑ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  14. ↑ "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008.
  15. ↑ skywatchers
  16. ↑ 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: 430. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  17. ↑ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 355. ISBN 0-486-21079-0. Retrieved 2012-09-04.
  18. ↑ (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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