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) −2.43 ± 0.94[1] mas
Distance 7,800[4] ly
(2,400 pc)
Details
Radius 1,009 ± 142[4] R
Luminosity (bolometric) 176,000[4]-360,000[6] L
Surface gravity (log g) 0.0[4]-−0.5[6] cgs
Temperature 3,720 ± 183[4] K
Other designations
KW Sgr, CD−27°12032, HD 316496, HIP 87433, AAVSO 1745-28
Database references
SIMBAD data

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 of 1,009 R (up to 1,460 R by some estimates), 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.[7] 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 R based on the assumption of an effective temperature of 3,700 K.[6] 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 R 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. ^ a b c d e f Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b 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. ^ a b c 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. ^ a b c d e f g h i j k 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:1305.6179Freely accessible. 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. ^ a b c 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/0504337Freely accessible. Bibcode:2005ApJ...628..973L. doi:10.1086/430901. 
  7. ^ 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. 

External links[edit]

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