The Chemical Evolution of Globular Clusters I. Reactive Elements and
  Non-Metals
  We propose a new chemical evolution model aimed at explaining the chemical
properties of globular clusters (GC) stars. Our model depends upon the
existence of (i) a peculiar pre-enrichment phase in the GC's parent galaxy
associated with very low-metallicity Type II supernovae (SNeII), and (ii)
localized inhomogeneous enrichment from a single Type Ia supernova (SNeIa) and
intermediate-mass (4 7Msun) asymptotic giant branch (AGB) field stars. GC
formation is then assumed to take place within this chemically-peculiar region.
Thus, in our model the first low-mass GC stars to form are those with peculiar
abundances (i.e., O-depleted and Na-enhanced) while ``normal'' stars (i.e.,
O-rich and Na depleted) are formed in a second stage when self-pollution from
SNeII occurs and the peculiar pollution from the previous phase is dispersed.
In this study, we focus on three different GCs: NGC6752, NGC6205 (M13) and
NGC2808. We demonstrate that, within this framework, a model can be constructed
which is consistent with (i) the elemental abundance anti-correlations, (ii)
isotopic abundance patterns, and (iii) the extreme [O/Fe] values observed in
NGC2808 and M13, without violating the global constraints of approximately
unimodal [Fe/H] and C+N+O.
