NGC 6426

NGC 6426
HST image of NGC 6426
Observation data (J2000 epoch)
ClassIX[1]
ConstellationOphiuchus
Right ascension17h 44m 54.71s[2]
Declination+03° 10′ 12.5″[2]
Distance67 kly (20.6 kpc)[3]
Apparent magnitude (V)10.9[4]
Apparent dimensions (V)4.2′[4]
Physical characteristics
Metallicity = –2.34[3] dex
Estimated age13.0±1.5 Gyr[5]
Other designationsNGC 6426, Cr 346[6]
See also: Globular cluster, List of globular clusters

NGC 6426 is a globular cluster of stars located in the equatorial constellation of Ophiuchus. It was discovered by the German-English astronomer William Herschel on 3 June 1786.[7] This cluster is at a distance of 67,000 light years from the Sun.[3] It has an apparent visual magnitude of 10.9 and an angular diameter of 4.2′, making it difficult to observe with a small telescope.[4]

This cluster is orbiting in the outer galactic halo at a distance of 47 kly (14.4 kpc) from the Galactic Core. It is one of the oldest and most metal-poor clusters in the Milky Way system. NGC 6426 has an angular half-light radius of 0.92′ and a tidal radius of 13.0′,[3] with a Shapley–Sawyer Concentration Class of IX.[1] It is an estimated 13.0±1.5 billion years old.[5] Chemical abundances of four members at the tip of the red giant branch suggests there may have been at least two generations of stars, with the older stars enriching a younger generation with elements including Mg, Si, and Zn. There is also some indication of hypernova enrichment of the pre-cluster medium by lighter alpha process elements.[8]

Based on the spectra of a dozen identified RR Lyrae variables, this is classified as an Oosterhoff type II cluster.[9] In 2012, a carbon star was discovered near the center of the cluster.[10]

  1. ^ a b Cite error: The named reference Shapley_Sawyer_1927 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference Di_Criscienzo_et_al_2006 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference Koch_et_al_2018 was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference O'Meara_2007 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Dotter_et_al_2011 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference cseligman was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Hanke_et_al_2017 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Papadakis_et_al_2000 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Sharina_et_al_2012 was invoked but never defined (see the help page).