NGC 6426

NGC 6426
NGC 6426 imaged by Hubble Space Telescope
Observation data (J2000 epoch)
ClassIX
ConstellationOphiuchus
Right ascension17h 44m 54.71s
Declination+03° 10′ 12.5″
Distance67 kly (20.6 kpc)
Apparent magnitude (V)10.9
Apparent dimensions (V)4.2′
Physical characteristics
Metallicity[Fe/H] = –2.34 dex
Estimated age13.0±1.5 Gyr
Other designationsNGC 6426, Cr 346
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. This cluster is at a distance of 67,000 light years from the Sun. 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.

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′, with a Shapley–Sawyer Concentration Class of IX. It is an estimated 13.0±1.5 billion years old. 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.

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

References

  1. 1 2 Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin. 849: 11–14. Bibcode:1927BHarO.849...11S.
  2. 1 2 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.
  3. 1 2 3 4 Koch, Andreas; et al. (August 2018). "Kinematics of outer halo globular clusters: M 75 and NGC 6426". Astronomy & Astrophysics. 616. id. A74. arXiv:1805.06894. Bibcode:2018A&A...616A..74K. doi:10.1051/0004-6361/201833110.
  4. 1 2 3 O'Meara, Stephen James (2007). Herschel 400 Observing Guide. Cambridge University Press. p. 231. ISBN 9780521858939.
  5. 1 2 Dotter, Aaron; et al. (September 2011). "Globular Clusters in the Outer Galactic Halo: New Hubble Space Telescope/Advanced Camera for Surveys Imaging of Six Globular Clusters and the Galactic Globular Cluster Age-metallicity Relation". The Astrophysical Journal. 738 (1). id. 74. arXiv:1106.4307. Bibcode:2011ApJ...738...74D. doi:10.1088/0004-637X/738/1/74.
  6. ↑ "NGC 6426". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-08-19.
  7. ↑ Seligman, Courtney. "NGC 6426 (= GCL 76)". Celestial Atlas. Retrieved 15 October 2016.
  8. ↑ Hanke, M.; et al. (March 2017). "Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426". Astronomy & Astrophysics. 599. id. A97. arXiv:1612.05989. Bibcode:2017A&A...599A..97H. doi:10.1051/0004-6361/201629650.
  9. ↑ Papadakis, I.; et al. (February 2000). "The NGC 6426 RR Lyrae Variables and Horizontal-Branch Morphology". The Astronomical Journal. 119 (2): 851–858. Bibcode:2000AJ....119..851P. doi:10.1086/301221.
  10. ↑ Sharina, M.; et al. (October 2012). "A CH star in the globular cluster NGC 6426". Monthly Notices of the Royal Astronomical Society: Letters. 426 (1): L31–L35. arXiv:1207.4357. Bibcode:2012MNRAS.426L..31S. doi:10.1111/j.1745-3933.2012.01317.x.