Location of λ Sagittarii (circled) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18 27 58.24072 |
| Declination | −25° 25′ 18.1146″ |
| Apparent magnitude (V) | +2.813 |
| Characteristics | |
| Spectral type | K1IIIb |
| U−B color index | +0.903 |
| B−V color index | +1.045 |
| Astrometry | |
| Radial velocity (Rv) | −43.5 km/s |
| Proper motion (μ) | RA: −44.76 mas/yr Dec.: −185.66 mas/yr |
| Parallax (π) | 41.72 ± 0.16 mas |
| Distance | 78.2 ± 0.3 ly (23.97 ± 0.09 pc) |
| Absolute magnitude (MV) | 0.76±0.03 |
| Details | |
| Mass | 1.79±0.20 M☉ |
| Radius | 11.234±0.181 R☉ |
| Luminosity | 58.79±2.61 L☉ |
| Surface gravity (log g) | 2.66±0.10 cgs |
| Temperature | 4,768±36 K |
| Metallicity | −0.11±0.03 dex |
| Rotational velocity (v sin i) | 3.81 km/s |
| Other designations | |
| Kaus Borealis, λ Sgr, 22 Sagittarii, CPD−25 6523, FK5 692, GC 25180, HD 169916, HIP 90496, HR 6913, SAO 186841, PPM 268438 | |
| Database references | |
| SIMBAD | data |
Lambda Sagittarii (Latinized from λ Sagittarii), formally named Kaus Borealis /ˈkɔːs bɒriˈælɪs/, is a star in the southern constellation of Sagittarius. The star marks the top of the Archer's bow.
Properties
With an apparent visual magnitude of +2.81, this is one of the brighter members of the constellation and, according to the Bortle Dark-Sky Scale, it is readily visible to the naked eye. Based upon parallax measurements, it is 78.2 light-years (24.0 parsecs) from the Sun.
Being 2.1 degrees south of the ecliptic, Lambda Sgr is sometimes occulted by the Moon and, rarely, by a planet. The last planet to pass in front of it was Venus, on 19 November 1984. The previous occasion was 5 December 1865, when it was occulted by Mercury.
Kaus Borealis is a giant star with a stellar classification of K1 IIIb. It has a mass 1.8 times that of the Sun and a physical size of about 11.2 times the Sun's radius. This expanded outer envelope is radiating energy at an effective temperature of 4,768 K, causing it to glow with the cool orange hue of a K-type star. It appears to be rotating at a leisurely rate, with a projected rotational velocity of 3.81 km s.
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) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Kaus Borealis for this star.
This star, with Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii, Zeta Sagittarii, Sigma Sagittarii, Tau Sagittarii and Phi Sagittarii comprises the Teapot asterism.
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.
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 ( النعام الوارد ), "The Going Ostriches" and al-Naʽām al-Ṣādir (النعم الصادر), "The Returning Ostriches".
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 斗宿二 (Dǒu Sù èr, English: the Second Star of Dipper.)
References
- ^ 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.
- ^ Ottoni, G.; Udry, S.; Ségransan, D.; Buldgen, G.; Lovis, C.; Eggenberger, P.; Pezzotti, C.; Adibekyan, V.; Marmier, M.; Mayor, M.; Santos, N. C.; Sousa, S. G.; Lagarde, N.; Charbonnel, C. (2022-01-01). "CORALIE radial-velocity search for companions around evolved stars (CASCADES). I. Sample definition and first results: Three new planets orbiting giant stars". Astronomy and Astrophysics. 657: A87. arXiv:2201.01528. Bibcode:2022A&A...657A..87O. doi:10.1051/0004-6361/202040078. ISSN 0004-6361. Lambda Sagittarii's database entry at VizieR.
- ^ Keenan, Philip C.; McNeil, Raymond C. (1989-10-01). "The Perkins Catalog of Revised MK Types for the Cooler Stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373. ISSN 0067-0049. Lambda Sagittarii's database entry at VizieR.
- ^ Gutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards", Publ. Dept. Astron. Univ. Chile, 1, Publicaciones Universidad de Chile, Department de Astronomy: 1–17, Bibcode:1966PDAUC...1....1G.
- Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, 35 (35), Astronomisches Rechen-Institut Heidelberg: 1, Bibcode:1999VeARI..35....1W.
- ^ Rains, Adam D.; et al. (April 2020), "Precision angular diameters for 16 southern stars with VLTI/PIONIER", Monthly Notices of the Royal Astronomical Society, 493 (2): 2377–2394, arXiv:2004.02343, Bibcode:2020MNRAS.493.2377R, doi:10.1093/mnras/staa282, S2CID 214802418
- 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.
- "IAU Catalog of Star Names". Retrieved 28 July 2016.
- "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16.
- 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, S2CID 10436552.
- "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
- "Teapot". constellation-guide.com. Retrieved 2017-05-13.
- 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.
- 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.
- (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日 Archived 2011-05-22 at the Wayback Machine
