KW Sagittarii

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KW Sagittarii
Sagittarius IAU.svg
Location of KW Sgr
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 17h 52m 00.72665s[1]
Declination −28° 01′ 20.5622″[1]
Apparent magnitude (V) 11.0[2]

8.5 to 11 (AAVSO)[citation needed]
11.0 to 13.2 (p)[3]

Characteristics
Spectral type M1.5Iab[4] (M0I - M4Ia[3])
Apparent magnitude (K) 1.43[2]
U−B color index 3.21[4]
B−V color index 2.47[4]
V−R color index 2.58[4]
J−K color index 1.56[4]
Variable type SRc[3]
Astrometry
Radial velocity (Rv)−7.40[5] km/s
Proper motion (μ) RA: 0.39[1] mas/yr
Dec.: −1.62[1] mas/yr
Parallax (π)0.5281 ± 0.1392[6] mas
Distance7,800[4] ly
(2,400 pc)
Details
Radius1,009 ± 142[4], 1,460[7] R
Diameter1,009 ± 142[4], 1,460[7] D
Luminosity (bolometric)176,000+164,000
−87,000
[4], 363,000[7] L
Surface gravity (log g)0.0[4]-−0.5[7] cgs
Temperature3,720 ± 183[4] K
Other designations
KW Sgr, CD−27°12032, HD 316496, HIP 87433, AAVSO 1745-28
Database references
SIMBADdata

KW Sagittarii is a red supergiant, located approximately 2,400 parsecs away from our Sun in the direction of the constellation Sagittarius. It has a size over 1,000 D making it one of the largest known stars. If placed at the center of the Solar System, the star's surface would engulf Mars.

Distance[edit]

The distance of 2,400 parsecs is based on the assumption of membership on the Sagittarius OB5 association.[8] The parallax derived from the Hipparcos mission is negative so doesn't give much information about the distance except that it is likely to be large.[1]

Characteristics[edit]

Levesque calculate that the star has a bolometric luminosity of over 360,000 L and a radius around 1,460 D based on the assumption of an effective temperature of 3,700 K.[7] Marcaide calculate that the star has a bolometric luminosity of less than 200,000 L based on the measured flux and an assumed distance, and a radius around 1,009 ± 142 D based on the measured angular diameter and luminosity. The effective temperature was then derived from the luminosity and radius.[4]

AAVSO light curve of SRC variable star KW Sgr from 1 Jan 1990 to 24 Nov 2010. Up is brighter and down is fainter. Day numbers are Julian day.

References[edit]

  1. 1.0 1.1 1.2 1.3 1.4 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 2.0 2.1 Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues 2237. Bibcode 2002yCat.2237....0D.
  3. 3.0 3.1 3.2 KW Sgr, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line November 10, 2010. (Quick look: KW+Sgr)
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. (2013). "The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii". Astronomy & Astrophysics 554: A76. arXiv:1305.6179. Bibcode 2013A&A...554A..76A. doi:10.1051/0004-6361/201220920.
  5. Barbier-Brossat, M.; Petit, M.; Figon, P. (1994). "Third bibliographic catalogue of stellar radial velocities (Text in French)". Astronomy and Astrophysics Supplement Series 108. Bibcode 1994A&AS..108..603B.
  6. Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. arXiv:1804.09365. Bibcode 2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  7. 7.0 7.1 7.2 7.3 Levesque, E. M.; Massey, P.; Olsen, K. A. G.; Plez, B.; Josselin, E.; Maeder, A.; Meynet, G. (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal 628 (2): 973. arXiv:astro-ph/0504337. Bibcode 2005ApJ...628..973L. doi:10.1086/430901.
  8. Melnik, A. M.; Dambis, A. K. (2009). "VizieR Online Data Catalog: Velocity and proper motion of OB associations (Melnik+, 2009)". VizieR On-line Data Catalog: J/MNRAS/400/518. Originally published in: 2009MNRAS.400..518M 740. Bibcode 2009yCat..74000518M.


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External links[edit]

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