Analysis of Composite Spectra--the Ultra-violet Excess of Stars in Globular Clusters
1974; Oxford University Press; Volume: 167; Issue: 1 Linguagem: Inglês
10.1093/mnras/167.1.137
ISSN1365-2966
Autores Tópico(s)Galaxies: Formation, Evolution, Phenomena
ResumoUltra-violet excesses which are nearly independent of interstellar reddening are estimated for 38 globular clusters. A model-fitting process is used. The data are details of the observed upper part of each individual B–V, V array and the integrated U–B colours. By noting the effects of changes in the data, we assess errors in a way which may be applicable in other work on the integrated colours of clusters and galaxies. Inconsistencies in the available data are found. A provisional calibration of the ultra-violet excesses in terms of metal-content is possible. Other methods of ordering the clusters in metal-content are considered inferior, but Q = U–B –0.72( B–V ) is a useful rough indicator of ultra-violet excess. There is a possibly identifiable metal-rich subgroup of clusters, but each cluster has at least a small ultra-violet excess. The positions of the clusters in this subgroup imply that the Galaxy is enriched in metals in a 6 kpc thick, 18-kpc diameter ‘superdisk’. The metal-abundance in the superdisk is about one-third that of the Sun, and may explain the composition of the oldest disk stars. A preliminary explanation of the origin of the superdisk is that the collapse of the protogalaxy was retarded or reversed by the pressure of trapped radiation.
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