Globular cluster system of the galaxy. II. The spatial and metallicity distributions, the second parameter phenomenon, and the formation of the cluster system
The metal abundance measurements that were collected for 84 globular clusters in the first paper of this series are used here to describe the cluster system. The ranking of the clusters by metallicity has been calibrated by a new (Fe/H) scale, which is based in part on the measurement of (Fe/H)=-1.2 for M71. According to this scale, the metal abundance gradient between the inner and outer halo clusters (i.e., R<9 kpc and 9< or =R< 40 kpc) is only a small fraction of that found with previous (Fe/H) scales. It is not clear, however, that the new scale is to be preferred over the old ones; consequently the size of this gradient remains in doubt. The most significant properties of the cluster system that do not depend on the validity of the (Fe/H) scale are the following; (i) there is a wide range in metal abundance among the cluster in the zone 9< or =R<40 kpc, but no evidence of a gradient with R or with distance from the galactic plane, Vertical BarZVertical Bar; (ii) among the clusters with R<9 kpc, there is a metal abundance gradient with Vertical BarZVertical Bar; and (iii) the magnitude of the second parameter effect increases with R, and if age is the second parameter, then over the range 0<40 kpc, the mean cluster age declines by approx.3 Gyr and the scatter in age increases from less than 1 Gyr to approx.2 Gyr.
- Research Organization:
- Mount Wilson and Las Campanas Observatory, Carnegie Institution of Washington; and Yale University Observatory
- OSTI ID:
- 6848625
- Journal Information:
- Astrophys. J.; (United States), Vol. 241:2
- Country of Publication:
- United States
- Language:
- English
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