NGC 6401

NGC 6401
HST image of NGC 6401
Observation data (J2000 epoch)
ConstellationOphiuchus
Right ascension17h 38m 36.93s[1]
Declination−23° 54′ 31.5″[1]
Distance25.1 kly (7.70 kpc)[2]
Apparent magnitude (V)7.4[3]
Apparent dimensions (V)4.8′[3]
Physical characteristics
Metallicity = −1.15±0.20[4] dex
Estimated age13.2±1.2 Gyr[4]
Other designationsGC 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]

  1. ^ a b Cite error: The named reference Di_Criscienzo_et_al_2006 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference Baumgardt_et_al_2019 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference O'Meara_219 was invoked but never defined (see the help page).
  4. ^ a b c d Cite error: The named reference Cohen_et_al_2021b was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference NASA_ESA_Hubble was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference Tsapras_et_al_2017 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Cohen_et_al_2021a was invoked but never defined (see the help page).