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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]

Messier 23
Open cluster Messier 23 in Sagittarius
Observation data (J2000 epoch)
ConstellationSagittarius
Right ascension17h 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

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]




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.
  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.
  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. 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. 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.
  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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На других языках

[de] Messier 23

Messier 23 (M23, auch als NGC 6494 bezeichnet) ist einer der sechs hellsten offenen Sternhaufen im Sommersternbild Schütze (Sagittarius). Er hat eine Helligkeit von +5,5 mag und eine Winkelausdehnung von 27'. Der Haufen steht mit rund 2000 Lichtjahren Entfernung, auf halben Weg zwischen der Sonne und dem Sagittarius-Arm unserer Galaxis. Die Analyse des Farben-Helligkeits-Diagramms von Messier 23 ergibt ein Alter von rund 300 Millionen Jahren.[4]
- [en] Messier 23

[es] Cúmulo abierto M23

M23 (también conocido como NGC 6494) es un cúmulo abierto en la constelación de Sagitario cerca del límite con Ophiuchus, que puede apreciarse con prismáticos. Fue descubierto por Charles Messier el 20 de junio de 1764.

[ru] M 23 (звёздное скопление)

Рассеянное скопление M 23 — рассеянное звёздное скопление в созвездии Стрельца. Также известно как Объект Мессье 23.


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