Messier 26

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.[lower-alpha 1] 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]

Messier 26
Open cluster Messier 26
Credit: Hillary Mathis, Vanessa Harvey, REU program/NOIRLab/NSF/AURA
Observation data (J2000.0 epoch)
ConstellationScutum
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

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)

Footnotes and references

Footnotes
  1. On June 20

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. 431, ISBN 978-0596526856
  4. 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. Burnham, Robert (1978), Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System, Dover books on astronomy, 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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