Astronomy:KW Sagittarii

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Short description: Star in the constellation Sagittarius
KW Sagittarii
Observation data
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]
Characteristics
Spectral type M1.5Iab[3] (M0I - M4Ia[4])
Apparent magnitude (K) 1.43[2]
U−B color index 3.21[3]
B−V color index 2.47[3]
V−R color index 2.58[3]
J−K color index 1.56[3]
Variable type SRc[4]
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
Distance7,890 ly
(2,420[lower-alpha 1][7] pc)
Absolute magnitude (MV)−7.7[8]
Details
Mass4.89+0.96
−0.07[9] M☉
Radius1,009±142[3] R☉
Luminosity (bolometric)176,000+164,000
−87,000[3] L☉
Surface gravity (log g)0.0[3] cgs
Temperature3,720±183[3] 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 1,900 parsecs (6,200 light-years) away from the Sun in the direction of the constellation Sagittarius. It is one of the largest-known stars. If placed at the center of the Solar System, the star's surface would engulf Mars.

Variability

AAVSO light curve of KW Sgr from 1 January 1990 to 24 November 2010. Up is brighter and down is fainter. Day numbers are Julian day.

KW Sagitarii was discovered to be variable in 1928 from a study of photographic plates.[10] It varies erratically in brightness over a range of about two magnitudes.[11] It is classified as a semiregular variable,[4] although the listed period of 670 days is poorly defined.[11] The peculiar cool spectrum has led to comparisons with symbiotic variables, but it is no longer considered to be a cataclysmic binary.[12]

Distance

A distance of 2,420 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] The Gaia Data Release 2 parallax is 0.5281±0.1392 mas and implies a distance of around 1,900 pc. A calculation using a prior based on known galactic structure gives a distance of 1,945+1,039
−511 pc.[13] The Gaia result carries a significant statistical margin of error, as well as an indicator that the astrometric excess noise is far beyond acceptable levels so that the parallax should be considered unreliable.[6]

Characteristics

KW Sagittarii is classed as a luminous cool supergiant and varies its spectral type between M0 and M4.[4] A 2005 study led by Levesque, using a MARCS model, calculated a high luminosity of 363,000 L☉ for KW Sgr and consequently very large radius of 1,460 R☉ based on the assumption of an effective temperature of 3,700 K at a distance of 3,000 pc. The star was then described as among the four largest and most luminous galactic red supergiants, which includes V354 Cephei, KY Cygni and Mu Cephei.[14]

More recently, KW Sagittarii was calculated to have a lower bolometric luminosity around 200,000 L☉ and a radius around 1,009 ± 142 R☉ was based on the measured angular diameter and luminosity.[3][15]

See also

Notes

  1. ↑ Assumed as KW Sagittarii is assumed to be part of Sgr OB5 association

References

  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): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  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 3.3 3.4 3.5 3.6 3.7 3.8 3.9 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. doi:10.1051/0004-6361/201220920. Bibcode: 2013A&A...554A..76A. 
  4. ↑ 4.0 4.1 4.2 4.3 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)
  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: 603. Bibcode: 1994A&AS..108..603B. 
  6. ↑ 6.0 6.1 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G.  Gaia DR2 record for this source at VizieR.
  7. ↑ 7.0 7.1 Melnik, A. M.; Dambis, A. K. (2020). "Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions". Astrophysics and Space Science 365 (7): 112. doi:10.1007/s10509-020-03827-0. Bibcode: 2020Ap&SS.365..112M. 
  8. ↑ Massey, Philip; Silva, David R.; Levesque, Emily M.; Plez, Bertrand; Olsen, Knut A. G.; Clayton, Geoffrey C.; Meynet, Georges; Maeder, Andre (2009). "Red Supergiants in the Andromeda Galaxy (M31)". The Astrophysical Journal 703 (1): 420. doi:10.1088/0004-637X/703/1/420. Bibcode: 2009ApJ...703..420M. 
  9. ↑ Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A. et al. (2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics 628: A94. doi:10.1051/0004-6361/201935765. Bibcode: 2019A&A...628A..94A. 
  10. ↑ Woods, Ida E. (1928). "Tenth Magnitude Nova in Sagittarius". Harvard College Observatory Bulletin 861: 5. Bibcode: 1928BHarO.861....5W. 
  11. ↑ 11.0 11.1 Swope, Henrietta Hill (1942). "Variable stars in MWF 189". Annals of Harvard College Observatory 109: 1. Bibcode: 1942AnHar.109....1S. 
  12. ↑ Downes, Ronald A.; Webbink, Ronald F.; Shara, Michael M.; Ritter, Hans; Kolb, Ulrich; Duerbeck, Hilmar W. (2001). "A Catalog and Atlas of Cataclysmic Variables: The Living Edition". Publications of the Astronomical Society of the Pacific 113 (784): 764. doi:10.1086/320802. Bibcode: 2001PASP..113..764D. 
  13. ↑ Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Mantelet, G.; Andrae, R. (2018). "Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2". The Astronomical Journal 156 (2): 58. doi:10.3847/1538-3881/aacb21. Bibcode: 2018AJ....156...58B. 
  14. ↑ 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): 973–985. doi:10.1086/430901. Bibcode: 2005ApJ...628..973L. 
  15. ↑ Mauron, N.; Josselin, E. (2011). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy and Astrophysics 526: A156. doi:10.1051/0004-6361/201013993. Bibcode: 2011A&A...526A.156M. 

External links



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