A self contamination model for the formation of globular star clusters
Brown, James Howard
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https://hdl.handle.net/2142/23872
Description
Title
A self contamination model for the formation of globular star clusters
Author(s)
Brown, James Howard
Issue Date
1991
Doctoral Committee Chair(s)
Truran, James W.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
globular cluster formation
self contamination model
globular star clusters
Language
en
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.
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