NGC 2420 explained

NGC 2420
Type:Open Cluster
Epoch:J2000
Constellation:Gemini
Ra:[1]
Dist Ly:10,060 ly[2]
Dist Pc:3,085 pc
Appmag V:8.3
Size V:6.4'
Age:2 billion years
Names:Melotte 69, Collinder 154

NGC 2420 is an open cluster in the constellation Gemini. It was discovered by William Herschel in 1783. The cluster is about two billion years old and it is located 10,000 light years away.

Observation

NGC 2420 lies about 6,5 degrees south-southeast of the star Pollux and a bit over two degrees east-northeast of the Eskimo Nebula. Through a small telescope at low magnification it appears as a uniform ghostly light that gets brighter to the centre, similar to a tail-less comet and at x33 magnification some individual stars can be glimpsed with averted vision. At higher magnification the cluster is resolved into a rich field of individual stars. It is included in the Herschel 400 Catalogue.[3] [4]

Characteristics

The cluster is located at a greater distance from the galactic centre than the Sun, lying in the direction of the galactic anti-centre, and lies 19° above the galactic plane, which corresponds to a distance of 3,000 light years. It has a Trumpler classification of I1r,[4] indicating a rich detached cluster with a central concentration made out of stars of similar apparent magnitude. Photographic photometry down to magnitude 19 indicates that the cluster has over 500 members, with the brightest being of 11th magnitude.[5] The total number of members is estimated to be around 1,000 within a diameter of 30 light years.[6]

It is estimated that 41% of the stars of the cluster are binaries.[7] The cluster has been found to contain two binary systems made out of two blue stragglers, while a third binary system is made out of a blue straggler and an extremely low mass white dwarf. These binary stars shine bright in far ultraviolet.[8] Using data from the Hubble Space Telescope, von Hippel and Gilmore detected eight white dwarf candidates and estimated a cooling age of about 2 billion years.[9]

The metallicity of the cluster has been a subject of many studies and has been found to be a bit sub-solar, with a metallicity of -0.26 according to WEBDA.[2] The cluster was found to be a bit metal poor, with a [Fe/H] of -0.7 to -0.6 from spectrographic studies performed in the 1980s[10] [11] [12] while subsequent CCD photometry indicates of a higher metallicity of about -0.30.[13] Pancino et al. indicated a [Fe/H]= -0.05 ± 0.03 according to Pancino et al., which is close to the trend of metallicity descreasing with increasing distance from the galactic centre.[14] The red giants of the cluster have a mean metallicity of −0.16 ± 0.04.[15] Based on spectrographic data of the Gaia-ESO survey, the stars around the turnoff point have sub-solar metallicities but they increase for stars of smaller mass.[16]

The stars of the cluster have homogenous CN and CH molecular band strengths.[17] Similar low dispersion was observed in other elements.[15]

See also

Notes and References

  1. NGC 2420. 2017-06-19.
  2. Web site: WEBDA: Open cluster page . webda.physics.muni.cz . 16 June 2024.
  3. Book: O'Meara . Stephen James . Herschel 400 Observing Guide . 14 June 2007 . Cambridge University Press . 978-0-521-85893-9 . 75 . en.
  4. Book: O'Meara . Stephen James . Deep-Sky Companions: The Secret Deep . 30 June 2011 . Cambridge University Press . 978-1-139-50007-4 . 166–168 . en.
  5. West . Frederick R. . Photographic Photometry of the Galactic Cluster NGC 2420 . The Astrophysical Journal Supplement Series . September 1967 . 14 . 384 . 10.1086/190160. 1967ApJS...14..384W .
  6. Web site: Star Cluster with Surprising Similarities to Sun's Composition Offers Clues on Milky Way Evolution . www.noirlab.edu . 16 June 2024 . en.
  7. Thompson . Benjamin A. . Frinchaboy . Peter M. . Spoo . Taylor . Donor . John . The Binary INformation from Open Clusters Using SEDs (BINOCS) Project: Reliable Photometric Mass Determinations of Binary Star Systems in Clusters . The Astronomical Journal . 1 April 2021 . 161 . 4 . 160 . 10.3847/1538-3881/abde4c. free . 2101.07857 . 2021AJ....161..160T .
  8. Yadav . R. K. S. . Dattatrey . Arvind K. . Rangwal . Geeta . Subramaniam . Annapurni . Bisht . D. . Sagar . Ram . UOCS. XIII. Study of the Far-ultraviolet Bright Stars in the Open Cluster NGC 2420 Using AstroSat . The Astrophysical Journal . 1 February 2024 . 961 . 2 . 251 . 10.3847/1538-4357/ad13e8. free . 2024ApJ...961..251Y .
  9. von Hippel . Ted . Gilmore . Gerard . The White Dwarf Cooling Age of the Open Cluster NGC 2420 . The Astronomical Journal . September 2000 . 120 . 3 . 1384–1395 . 10.1086/301528. astro-ph/0006033 . 2000AJ....120.1384V .
  10. Cohen . J. G. . Abundances in globular cluster red giants. III - M71, M67, and NGC 2420 . The Astrophysical Journal . November 1980 . 241 . 981 . 10.1086/158412. 1980ApJ...241..981C .
  11. Smith . Verne V. . Suntzeff . Nicholas B. . Velocities and abundances of giant stars in the old open cluster NGC 2420 . The Astronomical Journal . February 1987 . 93 . 359 . 10.1086/114320. 1987AJ.....93..359S .
  12. Pilachowski . C. A. . Wallerstein . G. . Canterna . R. . The chemical compositions of stars in the globular cluster 47 Tucanae and the old disk cluster NGC 2420 . The Astrophysical Journal . January 1980 . 235 . L21 . 10.1086/183150. 1980ApJ...235L..21P .
  13. Anthony-Twarog . Barbara J. . Tanner . Delora . Cracraft . Misty . Twarog . Bruce A. . vby C a Hβ CCD Photometry of Clusters. VI. The Metal-deficient Open Cluster NGC 2420 . The Astronomical Journal . January 2006 . 131 . 1 . 461–472 . 10.1086/498304. astro-ph/0510047 . 2006AJ....131..461A .
  14. Pancino . E. . Carrera . R. . Rossetti . E. . Gallart . C. . Chemical abundance analysis of the open clusters Cr 110, NGC 2099 (M 37), NGC 2420, NGC 7789, and M 67 (NGC 2682) . Astronomy and Astrophysics . February 2010 . 511 . A56 . 10.1051/0004-6361/200912965. 0910.0723 . 2010A&A...511A..56P .
  15. Souto . Diogo . Cunha . K. . Smith . V. . Prieto . C. Allende . Pinsonneault . M. . Zamora . O. . García-Hernández . D. A. . Mészáros . Sz. . Bovy . J. . Pérez . A. E. García . Anders . F. . Bizyaev . D. . Carrera . R. . Frinchaboy . P. M. . Holtzman . J. . Ivans . I. . Majewski . S. R. . Shetrone . M. . Sobeck . J. . Pan . K. . Tang . B. . Villanova . S. . Geisler . D. . Chemical Abundances in a Sample of Red Giants in the Open Cluster NGC 2420 from Apogee . The Astrophysical Journal . 10 October 2016 . 830 . 1 . 35 . 10.3847/0004-637X/830/1/35. free . 1607.06102 . 2016ApJ...830...35S .
  16. Semenova . Ekaterina . Bergemann . Maria . Deal . Morgan . Serenelli . Aldo . Hansen . Camilla Juul . Gallagher . Andrew J. . Bayo . Amelia . Bensby . Thomas . Bragaglia . Angela . Carraro . Giovanni . Morbidelli . Lorenzo . Pancino . Elena . Smiljanic . Rodolfo . The Gaia -ESO survey: 3D NLTE abundances in the open cluster NGC 2420 suggest atomic diffusion and turbulent mixing are at the origin of chemical abundance variations . Astronomy & Astrophysics . November 2020 . 643 . A164 . 10.1051/0004-6361/202038833. 2007.09153 . 2020A&A...643A.164S .
  17. Carrera . R. . Martínez-Vázquez . C. E. . Searching for chemical inhomogeneities in open clusters: Analysis of the CN and CH molecular band strengths in NGC 2158, NGC 2420, NGC 2682, NGC 7789, and Berkeley 29⋆ . Astronomy & Astrophysics . December 2013 . 560 . A5 . 10.1051/0004-6361/201322048. 1308.4548 . 2013A&A...560A...5C .

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