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 (Lambda Sgr, λ Sagittarii, λ Sgr) is the Bayer designation for a star within the southern constellation of Sagittarius. The star marks the top of the Archer's bow, whence its traditional name Kaus Borealis.

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 Earth.[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.[9] 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.[10] It appears to be rotating at a leisurely rate, with a projected rotational velocity of 3.81 km s−1.[7]

Name and etymology

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:0708.1752, 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/0603770, 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:
    \begin{align} 2\cdot R_* & = \frac{(23.97\cdot 4.24\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 21.9\cdot R_{\bigodot} \end{align}
  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:0709.1145, 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. ↑ 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.
  10. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16.
  11. ↑ "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008.
  12. ↑ skywatchers
  13. ↑ 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.
  14. ↑ 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.
  15. ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日

External links

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