Model Atmospheres
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Parameters
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Models were computed for seven overall metallicities, \[M/H\] from $-$2.5 to 0.5, with a step size of 0.5 dex. For each of these seven overall \[M/H\] mixtures, 25 combinations of modified carbon and $\alpha$ element abundances were adopted: The modifications to the logarithmic C and $\alpha$ abundances are $-$1, $-$0.5, 0, 0.5, and 1 dex. This format resulted in a total of 175 subgrids with unique chemical compositions (Table 4). The $\alpha$ elements in MARCS are O, Ne, Mg, Si, S, Ar, Ca, and Ti. This composition scheme is exactly the same as the previous models found on the MARCS website. The systematic $\alpha$ abundance changes were chosen to overlap the scheme (Section 2.1) used in the ATLAS9 model calculations.

[lrrr]{} $[$M/H$]$ & $-$2.5 & 0.5 & 0.5\
$[$C/M$]$ & $-$1 & 1 & 0.5\
$[\alpha$/M$]$& $-$1 & 1 & 0.5\

[lrrrrrr]{} M, N, R, K & 3500 & 4000 & 100 & 0 & 3 & 0.5\
K, G & 4250 & 5500 & 250 & 0 & 3 & 0.5\
M, N, R, K & 3500 & 4000 & 100 & 3.5 & 5 & 0.5\
K, G & 4250 & 5500 & 