NGC 6426

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NGC 6426
NGC 6426 HST 11586 R814B606.png
HST image of NGC 6426
Observation data (J2000 epoch)
Class IX [1]
Constellation Ophiuchus
Right ascension 17h 44m 54.71s [2]
Declination +03° 10′ 12.5″ [2]
Distance 67  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 designations NGC 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]

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<span class="mw-page-title-main">Messier 62</span> Globular cluster in the constellation Ophiuchus

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NGC 6388 is a globular cluster of stars located in the southern constellation of Scorpius. The cluster was discovered by Scottish astronomer James Dunlop on May 13, 1826 using a 20 cm (9 in) reflector telescope. It was later determined to be a globular cluster by English astronomer John Herschel, who was able to resolve it into individual stars. NGC 6388 is located at a distance of approximately 35,600 light-years (10.90 kpc) from the Sun. Due to its apparent visual magnitude of +6.8, binoculars or a small telescope are required to view it.

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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 .
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