NGC 121

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NGC 121
Potw1428a.tif
Hubble Space Telescope image of globular cluster NGC 121
Observation data (J2000 epoch)
Constellation Tucana
Right ascension 00h 26m 49.0s [1]
Declination −71° 32′ 10″ [1]
Distance 200  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 radius 143″ [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]

Contents

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]

Related Research Articles

<span class="mw-page-title-main">Globular cluster</span> Spherical collection of stars

A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".

<span class="mw-page-title-main">Local Group</span> Group of galaxies that includes the Milky Way

The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly 3 megaparsecs (10 million light-years; 9×1019 kilometres), and a total mass of the order of 2×1012 solar masses (4×1042 kg). It consists of two collections of galaxies in a "dumbbell" shape; the Milky Way and its satellites form one lobe, and the Andromeda Galaxy and its satellites constitute the other. The two collections are separated by about 800 kiloparsecs (3×10^6 ly; 2×1019 km) and are moving toward one another with a velocity of 123 km/s. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster. The exact number of galaxies in the Local Group is unknown as some are occluded by the Milky Way; however, at least 80 members are known, most of which are dwarf galaxies.

<span class="mw-page-title-main">Large Magellanic Cloud</span> Magellanic spiral galaxy that is a satellite of the Milky Way in the constellation Dorado

The Large Magellanic Cloud (LMC) is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (163,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal (c. 16 kiloparsecs (52,000 light-years) away) and the possible dwarf irregular galaxy called the Canis Major Overdensity. Based on the D25 isophote at the B-band (445 nm wavelength of light), the Large Magellanic Cloud is about 9.86 kiloparsecs (32,200 light-years) across. It is roughly one-hundredth the mass of the Milky Way and is the fourth-largest galaxy in the Local Group, after the Andromeda Galaxy (M31), the Milky Way, and the Triangulum Galaxy (M33).

<span class="mw-page-title-main">Small Magellanic Cloud</span> Dwarf irregular galaxy, satellite galaxy of the Milky Way

The Small Magellanic Cloud (SMC), or Nubecula Minor, is a dwarf galaxy near the Milky Way. Classified as a dwarf irregular galaxy, the SMC has a D25 isophotal diameter of about 5.78 kiloparsecs (18,900 light-years), and contains several hundred million stars. It has a total mass of approximately 7 billion solar masses. At a distance of about 200,000 light-years, the SMC is among the nearest intergalactic neighbors of the Milky Way and is one of the most distant objects visible to the naked eye.

<span class="mw-page-title-main">Tarantula Nebula</span> H II region in the constellation Dorado

The Tarantula Nebula is a large H II region in the Large Magellanic Cloud (LMC), forming its south-east corner.

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

Messier 62 or M62, also known as NGC 6266, is a globular cluster of stars in the south of the equatorial constellation of Ophiuchus. It was discovered in 1771 by Charles Messier, then added to his catalogue eight years later.

<span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

<span class="mw-page-title-main">47 Tucanae</span> Globular cluster in the constellation Tucana

47 Tucanae or 47 Tuc is a globular cluster located in the constellation Tucana. It is about 4.45 ± 0.01 kpc (15,000 ± 33 ly) away from Earth, and 120 light years in diameter. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 44 arcminutes across including its far outreaches. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa.

<span class="mw-page-title-main">NGC 1569</span> Galaxy in the constellation Camelopardalis

NGC 1569 is a dwarf irregular galaxy in Camelopardalis. The galaxy is relatively nearby and consequently, the Hubble Space Telescope can easily resolve the stars within the galaxy. The distance to the galaxy was previously believed to be only 2.4 Mpc. However, in 2008 scientists studying images from Hubble calculated the galaxy's distance at nearly 11 million light-years away, about 4 million light-years farther than previously thought, meaning it is a member of the IC 342 group of galaxies.

<span class="mw-page-title-main">NGC 1850</span> Super star cluster in the constellation Dorado

NGC 1850 is a double cluster and a super star cluster in the Dorado constellation, located in the northwest part of the bar of the Large Magellanic Cloud, at a distance of 168 kly (51.5 kpc) from the Sun. It was discovered by Scottish astronomer James Dunlop in 1826.

<span class="mw-page-title-main">R136</span> Super star cluster in the constellation Dorado, in the Large Magellanic Cloud

R136 is the central concentration of stars in the NGC 2070 star cluster, which lies at the centre of the Tarantula Nebula in the Large Magellanic Cloud. When originally named it was an unresolved stellar object but is now known to include 72 class O and Wolf–Rayet stars within 5 parsecs of the centre of the cluster. The extreme number and concentration of young massive stars in this part of the LMC qualifies it as a starburst region.

<span class="mw-page-title-main">NGC 602</span> Open cluster in the constrellation Hydrus

NGC 602 is a young, bright open cluster of stars located in the Small Magellanic Cloud (SMC), a satellite galaxy to the Milky Way. It is embedded in a nebula known as N90.

<span class="mw-page-title-main">NGC 346</span> Open cluster in the constellation Tucana

NGC 346 is a young open cluster of stars with associated nebula located in the Small Magellanic Cloud (SMC) that appears in the southern constellation of Tucana. It was discovered August 1, 1826 by Scottish astronomer James Dunlop. J. L. E. Dreyer described it as, "bright, large, very irregular figure, much brighter middle similar to double star, mottled but not resolved". On the outskirts of the cluster is the multiple star system HD 5980, one of the brightest stars in the SMC.

<span class="mw-page-title-main">NGC 290</span> Open cluster in the constellation Tucana

NGC 290 is an open cluster of stars in the southern constellation of Tucana. This cluster was discovered September 5, 1826, by Scottish astronomer James Dunlop. It lies some 200,000 light years away from the Sun in the Small Magellanic Cloud galaxy. The cluster is an estimated 30–63 million years old and is around 65 light years across.

<span class="mw-page-title-main">NGC 6934</span> Globular cluster in the constellation Delphinus

NGC 6934 is a globular cluster of stars in the northern constellation of Delphinus, about 52 kilolight-years distant from the Sun. It was discovered by the German-born astronomer William Herschel on 24 September 1785. The cluster is following a highly eccentric orbit through the Milky Way along an orbital plane that is inclined by 73° to the galactic plane. It may share a common dynamic origin with NGC 5466. As of 2018, it has been poorly studied.

<span class="mw-page-title-main">NGC 4449</span> Galaxy in the constellation Canes Venatici

NGC 4449, also known as Caldwell 21, is an irregular Magellanic type galaxy in the constellation Canes Venatici, being located about 13 million light-years away. It is part of the M94 Group or Canes Venatici I Group that is relatively close to the Local Group hosting our Milky Way galaxy.

<span class="mw-page-title-main">NGC 2808</span> Globular cluster in the constellation Carina

NGC 2808 is a globular cluster in the constellation Carina. The cluster belongs to the Milky Way, and is one of our home galaxy's most massive clusters, containing more than a million stars. It is estimated to be 12.5-billion years old.

<span class="mw-page-title-main">NGC 6352</span> Globular cluster in the constellation Ara

NGC 6352 is a globular cluster of stars in the southern constellation of Ara, located approximately 18.3 kly from the Sun. It was discovered by Scottish astronomer James Dunlop on May 14, 1826. The cluster has a Shapley–Sawyer Concentration Class of XI:. A telescope with a 15 cm (5.9 in) aperture is required to resolve the stars within this loose cluster.

<span class="mw-page-title-main">NGC 376</span> Globular cluster located in the constellation Tucana

NGC 376 is a young open cluster of stars in the southern constellation of Tucana. It was discovered on September 2, 1826, by Scottish astronomer James Dunlop. Dreyer, a Danish/British astronomer, described it as a "globular cluster, bright, small, round." It is irregular in form, with a central spike.

References

  1. 1 2 3 4 5 6 7 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. 1 2 3 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. 1 2 3 4 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. 1 2 3 4 5 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 .

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