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]
| NGC 6426 | |
|---|---|
 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 age | 13.0±1.5 Gyr[5] |
| Other designations | NGC 6426, Cr 346[6] |
![{\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4c0821bd80891e071c08e7c7ee8e022baedf522c)
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]
References
edit- ^ a b Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin. 849: 11–14. Bibcode:1927BHarO.849...11S.
- ^ a b 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.
- ^ a b c d 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.
- ^ a b c O'Meara, Stephen James (2007). Herschel 400 Observing Guide. Cambridge University Press. p. 231. ISBN 9780521858939.
- ^ a b 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.
- ^ "NGC 6426". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-08-19.
- ^ Seligman, Courtney. "NGC 6426 (= GCL 76)". Celestial Atlas. Retrieved 15 October 2016.
- ^ 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.
- ^ 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.
- ^ 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.
External links
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Media related to NGC 6426 at Wikimedia Commons- Steinicke, Wolfgang. "Revised NGC Data for NGC 6426". Students for the Exploration and Development of Space. Retrieved 15 October 2016.
