Astronomy:Messier 23

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Short description: Open cluster in Sagittarius
Messier 23
M23 Eguivar
Open cluster Messier 23 in Sagittarius
Observation data (J2000 epoch)
ConstellationSagittarius
Right ascension 17h 57m 04s[1]
Declination−18° 59′ 06″
Distance2,050 ly (628 pc)[2]
Apparent magnitude (V)5.5[3]
Apparent dimensions (V)35′[2]
Physical characteristics
Mass1,206[4] M☉
Radius8 ly
Estimated age330±100 myr[5]
Other designationsM23, NGC 6494,[6] Cr 356, C 1753-190
See also: Open cluster, List of open clusters

Messier 23, also known as NGC 6494, is an open cluster of stars in the northwest of the southern constellation of Sagittarius.[7] It was discovered by Charles Messier in 1764.[lower-alpha 1][3] It can be found in good conditions with binoculars or a modestly sized telescope.[3] It is in front of "an extensive gas and dust network", which there may be no inter-association.[4] It is within 5° the sun's position (namely in mid-December) so can be occulted by the moon.[8]

The cluster is centered about 2,050 light years away. Estimates for the number of its members range from 169[9] up to 414, with a directly-counted mass of 1,206 M☉; 1,332 M☉ by application of the virial theorem.[4] The cluster is around 330 million years old with a near-solar metallicity of [Fe/H] = −0.04.[5] The brightest component (lucida) is of magnitude 9.3.[10] Five of the cluster members are candidate red giants,[11] while orange variable VV Sgr in the far south,[lower-alpha 2] is a candidate asymptotic giant branch star.[12]

A 6th-magnitude star, shown in the top-right corner, figures in the far north-west as a foreground star – HD 163245 (HR 6679). Its parallax shift is 9.8912±0.0518 mas, having taken into account proper motion, which means it is about 101 parsecs (330 ly) away.[13]

Gallery

  • Map showing the location of M23

See also

Footnotes and References

Footnotes

  1. ↑ On June 20
  2. ↑ east of blue-white 7th magnitude fellow member HD 163427

References

  1. ↑ Wu, Zhen-Yu et al. (November 2009), "The orbits of open clusters in the Galaxy", Monthly Notices of the Royal Astronomical Society 399 (4): 2146–2164, doi:10.1111/j.1365-2966.2009.15416.x, Bibcode: 2009MNRAS.399.2146W. 
  2. ↑ 2.0 2.1 Kharchenko, N. V. et al. (2005), "Astrophysical parameters of Galactic open clusters", Astronomy and Astrophysics 438 (3): 1163–1173, doi:10.1051/0004-6361:20042523, Bibcode: 2005A&A...438.1163K. 
  3. ↑ 3.0 3.1 3.2 Thompson, Robert; Thompson, Barbara (2007), Illustrated Guide to Astronomical Wonders: From Novice to Master Observer, DIY science, O'Reilly Media, Inc., p. 408, ISBN 978-0596526856, https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA408 
  4. ↑ 4.0 4.1 4.2 McNamara, B. J.; Sanders, W. L. (February 1983), "A virial mass determination of the open cluster NGC 6494", Astronomy and Astrophysics 118 (2): 361–362, Bibcode: 1983A&A...118..361M. 
  5. ↑ 5.0 5.1 Netopil, M.; Paunzen, E.; Heiter, U.; Soubiran, C. (2016), "On the metallicity of open clusters. III. Homogenised sample", Astronomy & Astrophysics 585: A150, doi:10.1051/0004-6361/201526370, Bibcode: 2016A&A...585A.150N. 
  6. ↑ "M 23". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=M+23. 
  7. ↑ Gilmour, Jess K. (2003), The Practical Astronomer's Deep-sky Companion, The Patrick Moore Practical Astronomy Series, Springer Science & Business Media, p. 121, ISBN 978-1852334741, https://books.google.com/books?id=3IpZrC0BeewC&pg=PP121. 
  8. ↑ Ridgway, S. T. et al. (February 1979), "Twenty-eight angular diameters for late-type stars by the lunar occultation technique", Astronomical Journal 84: 247–256, doi:10.1086/112414, Bibcode: 1979AJ.....84..247R.  See VV Sgr.
  9. ↑ Sanders, W. L.; Schroeder, R. (August 1980), "Membership in the open cluster NGC 6494", Astronomy and Astrophysics 88: 102–107, Bibcode: 1980A&A....88..102S. 
  10. ↑ Sanders, W. L. (September 1990), "UBV photometry of NGC 6494 and metallicity considerations", Astronomy and Astrophysics Supplement Series 84 (3): 615–618, Bibcode: 1990A&AS...84..615S. 
  11. ↑ Claria, J. J.; Lapasset, E. (November 15, 1989), "Multicolour photometry of red giants in three southern open clusters", Monthly Notices of the Royal Astronomical Society 241 (2): 301–310, doi:10.1093/mnras/241.2.301, Bibcode: 1989MNRAS.241..301C 
  12. ↑ Jura, M. (February 1987), "Mass-losing red giants in open clusters", Astrophysical Journal, Part 1 313: 743–749, doi:10.1086/165012, Bibcode: 1987ApJ...313..743J. 
  13. ↑ 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.

External links

Coordinates: Sky map 17h 56m 48s, −19° 01′ 00″



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