NGC 1818

NGC 1818
A Hubble Space Telescope (HST) image of NGC 1818
Observation data (J2000 epoch)
ConstellationDorado
Right ascension05h 04m 13.300s[1]
Declination−66° 26′ 05.47″[1]
Distance~164 kly (50 kpc)[2]
Apparent magnitude (V)9.7 (B band)[3]
Physical characteristics
Absolute magnitude−8.8[4]
Mass13,500+5,600
−3,700 M☉
Estimated age30[5] or 40 Myr[6]
Notable featuresRare young globular
See also: Globular cluster, List of globular clusters

NGC 1818 is a young globular cluster in the north-west part of the Large Magellanic Cloud, about 3.2 kpc from the center.[7] It was discovered by Scottish astronomer James Dunlop in 1826,[8] and has since been well studied.[4]

The cluster has an estimated core radius of 2.67 pc and a 90% light radius of 13.83 pc,[1] with a combined mass of around 13,500 times the mass of the Sun.[5] Age estimates for the cluster range from 25[7] to 40[6] million years. Given this, most stars with a mass equal to the Sun or less are still on the pre-main-sequence. The average stellar metallicity – what astronomers term the abundance of elements with higher atomic number than helium – is −0.4, or about 10−0.4 ≈ 40% of the abundance in the Sun.[4]

There appear to be two distinct stellar populations in the cluster with the more blue (hotter) stars showing slower rotation rates than the redder (cooler) stars.[6] The frequency of binary star systems in the cluster increases with distance from the core, which is the opposite of the normal trend for globular clusters. This may be explained by interactions with other stars in the denser core disrupting binary systems, before mass segregation of the cluster has begun to take effect.[5] The cluster contains few if any blue stragglers, which are the result of stellar mergers.[7]

  1. ^ a b c Cite error: The named reference Werchan2011 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference Hubble was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference simbad was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference Liu2009 was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference Geller2015 was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference Marino2018 was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference Johnsonetal2001 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Seligman was invoked but never defined (see the help page).