NGC 121

NGC 121
Potw1428a
Hubble Space Telescope image of globular cluster NGC 121
Observation data (J2000 epoch)
ConstellationTucana
Right ascension00h 26m 49.0s[1]
Declination−71° 32′ 10″[1]
Distance200 kly (60 kpc)[1]
Apparent magnitude (V)11.24[2]
Physical characteristics
Mass3.6+0.9
−0.7×105[1] M☉
Radius98 ly (30.2 pc)[1]
Tidal radius143″[3]
Metallicity = −1.28±0.03[4] dex
Estimated age10.5±0.5 Gyr[5]
See also: Globular cluster, List of globular clusters

NGC 121 is a globular cluster of stars in the southern constellation of Tucana. It is the oldest globular cluster in the Small Magellanic Cloud (SMC),[5] which is a dwarf satellite galaxy of the Milky Way. This cluster was first discovered by English astronomer John Herschel on September 20, 1835. The compiler of the New General Catalogue, Danish astronomer John Louis Emil Dreyer, described this object as "pretty bright, pretty small, little extended, very gradually brighter middle".[6] The cluster is located at a distance of around 200,000 light-years (60 kpc) from the Sun.[1]

This cluster forms part of the West Halo, a region that is moving outward with respect to the rest of the SMC.[7] It is located about 2.3° northwest of the SMC galactic center.[4] The cluster mass is 3.6×105 times the mass of the Sun.[1] The angular half-light radius of this cluster is 27.1″,[5] and the tidal radius is 143″.[3] It is positioned about ~32′ from the massive globular cluster 47 Tucanae, which has a tidal radius of 42.86′. Hence the two may be interacting.[5]

NGC 121 is the only old globular cluster in the SMC that is similar to Galactic clusters in the Milky Way.[4] Age estimates for this cluster range from 10.5 to 11.8 billion years old, which is 2-3 billion years younger than the oldest such comparable clusters in the Milky Way.[5] The aging giant stars in this cluster demonstrate that there are two distinct stellar populations, with the younger population being chemically enriched from the output of the first generation. The second generation forms a relatively low ~32% of the total population, but this amount is enhanced in the central portion of the cluster. This suggests the later generation is more centrally concentrated.[4][8]

RR Lyrae variable stars were detected in this cluster in 1988.[9] 20 candidate Dwarf Cepheid candidates were reported in 2008, including SX Phoenicis variables.[10] In 1998, 42 potential blue stragglers were identified via imaging by the Hubble Space Telescope.[3]

References

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  1. ^ a b c d e f g van Loon, J. Th.; et al. (November 2005). "Dust-enshrouded giants in clusters in the Magellanic Clouds". Astronomy and Astrophysics. 442 (2): 597–613. arXiv:astro-ph/0507571. Bibcode:2005A&A...442..597V. doi:10.1051/0004-6361:20053528.
  2. ^ "NGC 121". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2015-09-29.
  3. ^ a b c Shara, Michael M.; et al. (December 1998). "Hubble Space Telescope Observations of NGC 121: First Detection of Blue Stragglers in an Extragalactic Globular Cluster". The Astrophysical Journal. 508 (2): 570–575. Bibcode:1998ApJ...508..570S. doi:10.1086/306423.
  4. ^ a b c d Dalessandro, E.; et al. (October 2016). "Multiple Populations in the Old and Massive Small Magellanic Cloud Globular Cluster NGC 121". The Astrophysical Journal. 829 (2). id. 77. arXiv:1607.05736. Bibcode:2016ApJ...829...77D. doi:10.3847/0004-637X/829/2/77.
  5. ^ a b c d e Glatt, Katharina; et al. (April 2008). "An Accurate Age Determination for the Small Magellanic Cloud Star Cluster NGC 121 with the Hubble Space Telescope/Advanced Camera for Surveys". The Astronomical Journal. 135 (4): 1106–1116. Bibcode:2008AJ....135.1106G. doi:10.1088/0004-6256/135/4/1106.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ Seligman, Courtney. "New General Catalogue Objects: NGC 100-149". Celestial Atlas. Retrieved 2015-09-29.
  7. ^ Mucciarelli, A.; et al. (September 2023). "The chemical DNA of the Magellanic Clouds. II. High-resolution spectroscopy of the SMC globular clusters NGC 121, NGC 339, and NGC 419". Astronomy & Astrophysics. 677. id. A61. arXiv:2307.03470. Bibcode:2023A&A...677A..61M. doi:10.1051/0004-6361/202347120.
  8. ^ Niederhofer, F.; et al. (January 2017). "The search for multiple populations in Magellanic Cloud clusters - I. Two stellar populations in the Small Magellanic Cloud globular cluster NGC 121". Monthly Notices of the Royal Astronomical Society. 464 (1): 94–103. arXiv:1609.01595. Bibcode:2017MNRAS.464...94N. doi:10.1093/mnras/stw2269.
  9. ^ Walker, Alistair R.; Mack, Peter (September 1988). "CCD Photometry of the RR Lyrae Stars in NGC 121 and the Distance to the Small Magellanic Cloud". Astronomical Journal. 96: 872. Bibcode:1988AJ.....96..872W. doi:10.1086/114853.
  10. ^ Fiorentino, G.; et al. (January 2008). "Detection of new variable stars in the SMC cluster NGC 121". Memorie della Società Astronomica Italiana. 79: 3. arXiv:0801.2713.

Further reading

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  • Media related to NGC 121 at Wikimedia Commons
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