0. ](figure04.eps){width="3.5in"}

![Examples of how different \[C/M\] and \[$\alpha$/M\] content changes the temperature profile in the ATLAS9 and MARCS atmospheres for T$_{\rm eff}$ = 5500K, log $g$ = 4. For more details see the caption of Figure 6. ](figure05.eps){width="3.5in"}

Changes in model structures related to chemical composition
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Figures 4 and 5 illustrate the changes in the model structures in response to changes in chemical composition. The left-hand panels of Figure 4 (T$_{\rm eff} = 4000$K model) and 5 (T$_{\rm eff} = 5500$K) show the relative changes associated with variations of the carbon abundance from solar proportions. The ATLAS9 model for the warmer temperature has v$_{\rm t}$ = 2 km s$^{-1}$, while the MARCS model has v$_{\rm t}$ = 1 km s$^{-1}$, but this difference does not affect the model structures significantly. The relative variations found are very similar for MARCS and ATLAS9, except in the outermost layers of the atmosphere. The changes in the thermal structure are modest and show a behavior symmetric to that found for oxygen, which strongly suggests that CO formation is the driver of the variation. CO is the most tightly bound molecule and consumes almost all of the free atoms of either carbon or 