NGC 6401

File:320px

HST image of NGC 6401

Observation data (J2000 epoch)
Constellation| Ophiuchus
Right ascension|  17h 38m 36.93s[1]
Declination| −23° 54′ 31.5″[1]
Distance| 25.1 kly (7.70 kpc)[2]
Apparent magnitude (V)| 7.4[3]
Apparent dimensions (V)| 4.8′[3]
Physical characteristics
Metallicity| [Fe/H] = −1.15±0.20[4] dex
Estimated age| 13.2±1.2 Gyr[4]
Other designations| GC 4314, NGC 6301[5]
See also: Globular cluster, List of globular clusters

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. ↑ 1.0 1.1 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, doi:10.1111/j.1365-2966.2005.09819.x, Bibcode: 2006MNRAS.365.1357D.
2. ↑ 2.0 2.1 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, doi:10.1093/mnras/sty2997, Bibcode: 2019MNRAS.482.5138B.
3. ↑ 3.0 3.1 3.2 3.3 O'Meara, Stephen James (2007), Herschel 400 Observing Guide, Cambridge University Press, p. 219, ISBN 9780521858939, https://books.google.com/books?id=Nyh9fAC_tpIC&pg=PA219.
4. ↑ 4.0 4.1 4.2 4.3 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, doi:10.3847/1538-3881/ac281f, Bibcode: 2021AJ....162..228C.
5. ↑ "NGC 6401". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+6401.
6. ↑ "Enigmatic cluster targeted by Hubble", Hubble News (NASA/ESA), https://esahubble.org/images/potw1131a/, retrieved 2024-08-18.
7. ↑ 7.0 7.1 7.2 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, doi:10.1093/mnras/stw2773, Bibcode: 2017MNRAS.465.2489T.
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, doi:10.3847/1538-3881/abd036, Bibcode: 2021AJ....161...41C.
9. ↑ Meeus, Jan (2002). "Occultations of deep-sky objects during a total lunar eclipse". More Mathematical Astronomy Morsels. pp. 157-162. ISBN 0943396743. https://falakmu.id/khgt/dokumen/More mathematical astronomy morsels (Jean Meeus) (Z-Library).pdf.

## External links

* NGC 6401 SEDS.org (Revised NGC)
* NGC 6401 NASA Extragalactic Database

Coordinates:  17h 38m 36.93s, −23° 54′ 31.5″

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Astronomical catalogs

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* Astronomy:NGC 6396
* Astronomy:NGC 6397
* Astronomy:NGC 6398
* Astronomy:NGC 6399
* Astronomy:NGC 6400
* NGC 6401
* Astronomy:NGC 6402
* Astronomy:NGC 6403
* Astronomy:NGC 6404
* Astronomy:NGC 6405
* Astronomy:NGC 6406

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