the deeper layers. For the warmer models, this changes significantly, as more Fe and H is ionized, the overall number of electrons increases and the main electron contributors become Mg, Si, and Fe through most of the atmospheres.

Internal tests showed that polyatomic carbon molecules (C$_{2}$H$_{2}$, C3) substantially change the structure of the atmosphere with C/O ratios higher 1.7, if they are included in the linelist. These molecules significantly inflate the atmosphere changing the temperature in the line-forming photospheric layers. Since these molecules were used neither in the ATLAS9, nor in the MARCS calculations, atmospheric structures with C/O $>$ 1.7 and T$_{\rm eff} < 4000$K are not reliable and thus not published.

![Examples of the largest electron contributors to the total electron numbers in the ATLAS9 atmospheres for \[M/H\]=\[C/M\]=\[$\alpha$/M\] = 0. The figure shows the element electron numbers relative to the total number of electrons for the two models used in previous figures. The T$_{\rm eff} = 5500$K, log $g = 1$ model is plotted in the middle section to show that the electron contributors do not change significantly compared to a model with the same temperature but higher gravity. ](figure06.eps){width="3.5in"}

Conclusions
===========

Most of the ATLAS9 models are fully 