Messier 23

Messier 23
M23 Eguivar
Open cluster Messier 23 in Sagittarius
Observation data (J2000 epoch)
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
Associations
ConstellationSagittarius
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]

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]

  1. ^ Cite error: The named reference Wu2009 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference kharchenko2005 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Thompson2007 was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference McNamara1983 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference netopil2016 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Gilmour2003 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Ridgway1979 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Sanders1980 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Sanders1990 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Claria1989 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Jura1987 was invoked but never defined (see the help page).
  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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