Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global and non-global parameters of horizontal branch morphology of
  globular clusters   The horizontal branch (HB) morphology of globular clusters (GCs) is mainly
determined by metallicity. However, the fact that GCs with almost the same
metallicity exhibit different HB morphologies demonstrates that at least one
more parameter is needed to explain the HB morphology. It has been suggested
that one of these should be a global parameter that varies from GC to GC, and
the other a non-global parameter that varies within the GC. In this study we
provide empirical evidence corroborating this idea. We used the photometric
catalogs obtained with the Advanced Camera for Surveys (ACS) of the Hubble
Space Telescope (HST) and analyse the CMDs of 74 GCs. The HB morphology of our
sample of GCs has been investigated on the basis of the two new parameters L1
and L2 that measure the distance between the RGB and the coolest part of the
HB, and the color extension of the HB, respectively. We find that L1 correlates
with both metallicity and age, whereas L2 most strongly correlates with the
mass of the hosting GC. The range of helium abundance among the stars in a GC,
characterised by Delta Y and associated with the presence of multiple stellar
populations, has been estimated in a few GCs to date. In these GCs we find a
close relationship among Delta Y, GC mass, and L2. We conclude that age and
metallicity are the main global parameters while the range of helium abundance
within a GC is the main non-global parameter defining the HB morphology of
Galactic GCs.

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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
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The categories of this paper are: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: cs
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: atom-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph