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 on June 20, 1764. This 8th magnitude cluster is a challenge to find with typical binoculars, but can be spotted with an 80mm aperture. It is positioned near 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
2MASS Atlas image
Observation data (J2000.0 epoch)
ConstellationScutum
Right ascension 18h 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)

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.

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.