We present a new grid of stellar models and isochrones for old stellar populations, covering a large range of [Fe/H] values, for an heavy element mixture characterized by CNONa abundance anticorrelations as observed in Galactic globular cluster stars. The effect of this metal abundance pattern on the evolutionary properties of low mass stars, from the main sequence to the horizontal branch phase is analyzed. We perform comparisons between these new models, and our reference alpha-enhanced calculations, and discuss briefly implications for CMDs showing multiple main sequence or subgiant branches. A brief qualitative discussion of the effect of CN abundances on color-T_{eff} transformations is also presented, highlighting the need to determine theoretical color transformations for the appropriate metal mixture, if one wants to interpret observations in the Stroemgren system, or broadband filters blueward of the Johnson V-band.
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