GCl 38

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GCl 38
Observation data (J2000 epoch)
Constellation Hercules
Right ascension 16h 10m 59.00s[1]
Declination 14° 57′ 42.0″[1]
Distance 244,000 ly (74.7 kpc[2])
Apparent magnitude (V) 14.7[2]
Physical characteristics
VHB 20.0[2]
Estimated age 10 Ga[2]
Other designations Palomar 14, Arp 1, C1608 + 150[1]
See also: Globular cluster, List of globular clusters

GCl 38 is a globular cluster located in the constellation Hercules. It was discovered in 1958 by Sidney van den Bergh and Halton Arp during inspection of the photographic plates from the Palomar Sky Survey.[3] This is a round, diffuse cluster located in the outer halo of the Milky Way galaxy. It is about 3–4 billion years younger than a typical galactic cluster.[2]

The metallicity of the cluster is [Fe/H] = −1.50, indicating a lower abundance of elements with mass greater that helium compared to the Sun. The combined mass of the main sequence stars in the cluster is 1340 ± 50 solar masses, and the combined mass of observed stars within the half-light radius is 6020 ± 50 solar masses. (This is the inner radius of the cluster that emits half the total luminosity.) These mass estimates provide lower bounds for determining the total mass of the cluster. The median radial velocity of stars within the cluster is 72.19 ± 0.18 km/s.[4]

Because of the cluster's location on the outer fringes of the Milky Way, it was used as a test case for modified newtonian dynamics (MOND). This is an alternative hypothesis to explain the galactic rotation problem.[4]


  1. ^ a b c "GCl 38 -- Globular Cluster". SIMBAD Astronomical Database. Retrieved 2009-07-08. 
  2. ^ a b c d e Hilker, Michael (March 11, 2006). "Probable Member Stars of the Gravitational Theory-Testing Globular Clusters AM 1, Pal 3 and Pal 14". Astronomy and Astrophysics. 448 (1): 171–180. arXiv:astro-ph/0510679Freely accessible. Bibcode:2006A&A...448..171H. doi:10.1051/0004-6361:20054327. 
  3. ^ Arp, Halton; van den Bergh, Sidney (1960). "A New Faint Globular Cluster". Publications of the Astronomical Society of the Pacific. 72 (48): 48. Bibcode:1960PASP...72...48A. doi:10.1086/127473. 
  4. ^ a b Jordi, K.; Grebel, E. K.; Hilker, M.; Baumgardt, H.; Frank, M.; Kroupa, P.; Haghi, H.; CBtE, P.; Djorgovski, S. G. (2009). "Testing Fundamental Physics with Distant Star Clusters: Analysis of Observational Data on Palomar 14". The Astronomical Journal. 137 (6): 4586–4596. arXiv:0903.4448Freely accessible. Bibcode:2009AJ....137.4586J. doi:10.1088/0004-6256/137/6/4586.