Messier 23

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Messier 23
M23 Open Star Cluster.png
Open cluster Messier 23 in Sagittarius
Observation data (J2000 epoch)
Right ascension 17h 57m 04s [1]
Declination −18° 59′ 06″
Distance 2,050  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 designations M23, NGC 6494, [6] Cr 356, C 1753-190
Associations
Constellation Sagittarius
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. [a] [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]

Contents

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, [b] 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]

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, arXiv: 0909.3737 , Bibcode:2009MNRAS.399.2146W, doi: 10.1111/j.1365-2966.2009.15416.x , S2CID   6066790.
  2. 1 2 Kharchenko, N. V.; et al. (2005), "Astrophysical parameters of Galactic open clusters", Astronomy and Astrophysics, 438 (3): 1163–1173, arXiv: astro-ph/0501674 , Bibcode:2005A&A...438.1163K, doi:10.1051/0004-6361:20042523, S2CID   9079873.
  3. 1 2 3 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
  4. 1 2 3 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. 1 2 Netopil, M.; Paunzen, E.; Heiter, U.; Soubiran, C. (2016), "On the metallicity of open clusters. III. Homogenised sample", Astronomy & Astrophysics, 585: A150, arXiv: 1511.08884 , Bibcode:2016A&A...585A.150N, doi:10.1051/0004-6361/201526370, S2CID   118382876.
  6. ↑ "M 23". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved November 12, 2018.
  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.
  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, Bibcode:1979AJ.....84..247R, doi: 10.1086/112414 . 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, Bibcode:1989MNRAS.241..301C, doi: 10.1093/mnras/241.2.301
  12. ↑ Jura, M. (February 1987), "Mass-losing red giants in open clusters", Astrophysical Journal, Part 1, 313: 743–749, Bibcode:1987ApJ...313..743J, doi: 10.1086/165012 .
  13. ↑ Brown, A. G. A.; et al. (Gaia collaboration) (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 .
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