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Messier 26

Coordinates: Sky map 18h 45.2m 00s, −09° 24′ 00″
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Messier 26
Open cluster Messier 26
Credit: Hillary Mathis, Vanessa Harvey, REU program/NOIRLab/NSF/AURA
Observation data (J2000.0 epoch)
Right ascension18h 45m 18.0s[1]
Declination−09° 23′ 00″[1]
Distance5,160 ly (1,582 pc)[2]
Apparent magnitude (V)8.0[3]
Apparent dimensions (V)14′[3]
Physical characteristics
Radius11 ly[4]
Estimated age85.3[1] million years
Other designationsMessier 26, NGC 6694,[5] Cr 389, C 1842-094
Associations
ConstellationScutum
See also: Open cluster, List of open clusters

Messier 26, also known as NGC 6694, is an open cluster of stars in the southern constellation of Scutum. It was discovered by Charles Messier in 1764.[a] This 8th magnitude cluster is a challenge to find in ideal skies with typical binoculars, where it can be, with any modern minimum 3-inch (76 mm) aperture device. It is south-southwest of the open cluster Messier 11 and is 14′ across.[3] About 25 stars are visible in a telescope with a 150–200 mm (6–8 in) aperture.[6]

M26 spans a linear size of 22[4] light years across with a tidal radius of 25 light-years,[7] and is at a distance of 5,160[2] light years from the Earth. The brightest star is of magnitude 11[6] and the age of this cluster has been calculated to be 85.3[1] million years. It includes one known spectroscopic binary system.[8]

An interesting feature of M26 is a region of low star density near the nucleus. A hypothesis was that it was caused by an obscuring cloud of interstellar matter between us and the cluster, but a paper by James Cuffey suggested that this is not possible and that it really is a "shell of low stellar space density".[9] In 2015, Michael Merrifield of the University of Nottingham said that there is, as yet, no clear explanation for the phenomenon.[10]

  • Map showing the location of M26 (Roberto Mura)
    Map showing the location of M26 (Roberto Mura)

Footnotes and references

Footnotes

  1. ^ On June 20

References

  1. ^ a b c d 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.{{citation}}: CS1 maint: unflagged free DOI (link)
  2. ^ a b 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. ^ a b c Thompson, Robert; Thompson, Barbara (2007), Illustrated Guide to Astronomical Wonders: From Novice to Master Observer, DIY science, O'Reilly Media, Inc., p. 431, ISBN 978-0596526856
  4. ^ a b Kharchenko, N. V.; et al. (March 2009), "Shape parameters of Galactic open clusters", Astronomy and Astrophysics, 495 (3): 807–818, arXiv:0812.3542, Bibcode:2009A&A...495..807K, doi:10.1051/0004-6361/200810407.
  5. ^ "M 26". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 15, 2018.
  6. ^ a b Burnham, Robert (1978), Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Dover books on astronomy, vol. 3, Courier Corporation, p. 1756, ISBN 978-0486236735
  7. ^ Piskunov, A. E.; et al. (January 2008), "Tidal radii and masses of open clusters", Astronomy and Astrophysics, 477 (1): 165–172, Bibcode:2008A&A...477..165P, doi:10.1051/0004-6361:20078525.
  8. ^ Mermilliod, J. -C.; et al. (October 2007), "Red giants in open clusters. XIII. Orbital elements of 156 spectroscopic binaries", Astronomy and Astrophysics, 473 (3): 829–845, Bibcode:2007A&A...473..829M, doi:10.1051/0004-6361:20078007.
  9. ^ Cuffey, James (1940). "The Galactic Clusters NGC 6649 and NGC 6694". Astrophysical Journal. 92: 303. Bibcode:1940ApJ....92..303C. doi:10.1086/144220.
  10. ^ Merrifield, Michael (Oct 2, 2015). "M26 - Open Cluster". Deep Sky Videos. University of Nottingham/University of Sheffield. Retrieved March 29, 2016.
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