NGC 6401 is a globular cluster in the equatorial constellation of Ophiuchus.[3] This star cluster was discovered by German-English astronomer William Herschel in 1784, but he mistakenly classified it as a bright nebula. Later, his son John Herschel came to the same conclusion because the technology of the day did not allow the individual stars to be visually resolved.[6] It is visible in a small telescope, with an apparent visual magnitude of 7.4 and an angular diameter of 4.8′.[3]

This cluster is located at a distance of 25.1 kly (7.70 kpc) from the Sun[2] and is orbiting in the galactic bulge, in the inner part of the Milky Way galaxy.[4] Because of its high mass, it may be gravitationally trapped inside the Milky Way's bar. From the perspective of the Earth, this cluster is situated 5.3° from the Galactic Center and is strongly reddened due to extinction from interstellar dust.[7] NGC 6401 is a very old cluster with an estimated age of 13.2±1.2 Gyr,[4] but has not undergone core collapse.[8] It has a cluster radius of 2.4′.[7]

23 class ab and 11 class c RR Lyrae variables have been identified within a cluster radius of the core. From this, it is deduced that this is an Oosterhoff type I (Oo I) cluster.[7]

During the June 2011 lunar eclipse, a Total Lunar Eclipse, it was occulted by the Moon over Europe, North Africa and Southwest Asia. This will happen again during the June 2076 lunar eclipse over Eastern North America, Cuba, the Atlantic Ocean, Southeast Europe and the northern half of Africa.[9]: 160 

References

  1. ^ a b Di Criscienzo, M.; et al. (February 2006), "RR Lyrae-based calibration of the Globular Cluster Luminosity Function", Monthly Notices of the Royal Astronomical Society, 365 (4): 1357–1366, arXiv:astro-ph/0511128, Bibcode:2006MNRAS.365.1357D, doi:10.1111/j.1365-2966.2005.09819.x, S2CID 17838243.
  2. ^ a b Baumgardt, H.; Hilker, M.; Sollima, A.; Bellini, A. (2019), "Mean proper motions, space orbits, and velocity dispersion profiles of Galactic globular clusters derived from Gaia DR2 data", Monthly Notices of the Royal Astronomical Society, 482 (4): 5138–5155, arXiv:1811.01507, Bibcode:2019MNRAS.482.5138B, doi:10.1093/mnras/sty2997.
  3. ^ a b c d O'Meara, Stephen James (2007), Herschel 400 Observing Guide, Cambridge University Press, p. 219, ISBN 9780521858939.
  4. ^ a b c d Cohen, Roger E.; et al. (December 2021), "Relative Ages of Nine Inner Milky Way Globular Clusters from Proper-motion-cleaned Color-Magnitude Diagrams", The Astronomical Journal, 162 (6), id. 228, arXiv:2109.08708, Bibcode:2021AJ....162..228C, doi:10.3847/1538-3881/ac281f.
  5. ^ "NGC 6401". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-08-18.
  6. ^ "Enigmatic cluster targeted by Hubble", Hubble News, NASA/ESA, retrieved 2024-08-18.
  7. ^ a b c Tsapras, Y.; et al. (February 2017), "Variable stars in the bulge globular cluster NGC 6401", Monthly Notices of the Royal Astronomical Society, 465 (2): 2489–2504, arXiv:1610.09911, Bibcode:2017MNRAS.465.2489T, doi:10.1093/mnras/stw2773.
  8. ^ Cohen, Roger E.; et al. (January 2021), "Structure and Internal Kinematics of Nine Inner Milky Way Globular Clusters", The Astronomical Journal, 161 (1), id. 41, arXiv:2012.00791, Bibcode:2021AJ....161...41C, doi:10.3847/1538-3881/abd036.
  9. ^ Meeus, Jan (2002). "Occultations of deep-sky objects during a total lunar eclipse". More Mathematical Astronomy Morsels (PDF). pp. 157–162. ISBN 0943396743.


Allikas: http://en.wikipedia.org/wiki/NGC_6401
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