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Title:A self-contamination model for the formation of globular star clusters
Author(s):Brown, James Howard
Doctoral Committee Chair(s):Truran, James W.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Physics, Astronomy and Astrophysics
Abstract:This thesis describes a model of globular cluster formation which allows the self contamination of the cluster by an earlier generation of massive stars. It is first shown that such self-contamination naturally produces an (Fe/H) in the range from $-$2.5 to $-$1.0, precisely the same range observed in the metal poor (halo) globular clusters; this also seems to require that the disk clusters started with a substantial initial metallicity. To minimize the problem of creating homogeneous globular clusters, the second (currently observed) generation of stars is assumed to form in the expanding supershell around the first generation stars. Both numerical and analytic models are used to address this problem. The most important result of this investigation was that the late evolution of the supershell is the most important, and that this phase of the evolution is dominated by the external medium in which the cloud is embedded. This result and the requirement that only the most tightly bound systems may become globular clusters lead to the conclusion that a globular cluster with the mass and binding energy typically observed can be formed at star formation efficiencies as low as 10-20%. Furthermore, self contamination requires that the typical (Fe/H) of a bound system be about $-$1.6, independent of the free parameters of the model, allowing the clusters and field stars to form with different metallicity distributions in spite of their forming at the same time. Since the formation of globular clusters in this model is tied to the external pressure, the halo globular cluster masses and distribution can be used as probes of the early galactic structure. In particular, this model requires an increase in the typical globular cluster mass as one moves out from the galactic center; the masses of the halo clusters are examined, and they show considerable evidence for such a gradient. Based on a pressure distribution derived from this data, the effect of the galactic tidal field on the model is also investigated using an N-body simulation.
Issue Date:1991
Rights Information:Copyright 1991 Brown, James Howard
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9136554
OCLC Identifier:(UMI)AAI9136554

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