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NGC 121

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NGC 121
Potw1428a
Hubble Space Telescope image of globular cluster NGC 121
Observation data (J2000epoch)
ConstellationTucana
Right ascension00h26m49.0s[1]
Declination−71° 32′ 10″[1]
Distance200kly(60kpc)[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±0.5Gyr[5]
See also:Globular cluster,List of globular clusters

NGC 121is aglobular clusterof stars in the southernconstellationofTucana.It is the oldest globular cluster in theSmall Magellanic Cloud(SMC),[5]which is a dwarfsatellite galaxyof theMilky Way.This cluster was first discovered by English astronomerJohn Herschelon September 20, 1835. The compiler of theNew General Catalogue,Danish astronomerJohn 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 200,000light-years(60kpc) 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 is3.6×105times themass of the Sun.[1]The angularhalf-light radiusof this cluster is27.1″,[5]and the tidal radius is143″.[3]It is positioned about~32′from the massive globular cluster47 Tucanae,which has atidal radiusof42.86′.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 aginggiant starsin 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 variablestars were detected in this cluster in 1988.[9]20 candidateDwarf Cepheidcandidates were reported in 2008, includingSX Phoenicis variables.[10]In 1998, 42 potentialblue stragglerswere identified via imaging by theHubble Space Telescope.[3]

References

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  1. ^abcdefgvan 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.Retrieved2015-09-29.
  3. ^abcShara, 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. ^abcdDalessandro, 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. ^abcdeGlatt, 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.Retrieved2015-09-29.
  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 toNGC 121at Wikimedia Commons
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