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Effects of metallicity changes

The effects of metallicity changes on low resolution synthetic spectra are shown in Figs. 5-8 for models with $\hbox{$\,T_{\rm eff}$}=3400\,{\rm K}$ and $\hbox{$\,T_{\rm eff}$}=2400\,{\rm K}$ for the extreme values of the gravity in our grid. For the higher effective temperature, Figs. 5 and 6, the effects of metallicity are most pronounced in the optical (reduced metallicity causes increased flux due to decreased TiO opacity) and in region from 1 to $1.5\,\mu$m (the reaction of the atmosphere causes reduced flux in this region to compensate for the larger flux in the optical). The water band get stronger with reduced metallicity due to these redistribution effects. For lower effective temperatures, Figs. 7 and 8, the effects of metallicity of the spectra are significantly smaller, in particular for the lower gravity shown in Fig. 7. Here the temperatures are so low that the bands are saturated and thus will not change much within the range of metallicities considered here (larger changes will eventually affect the spectra). Significant changes occur only in localized bands, e.g., the metal hydrides and other non-saturated bands such as VO.

Peter H. Hauschildt