Teff and log g dependence of FeH in M‐dwarfs

We present synthetic FeH band spectra in the z‐filter range for several M‐dwarf models with log g = 3.0–5.0 [cgs] and Teff = 2800 K–3450 K. Our aim is to characterize convective velocities in M‐dwarfs and to give a rough estimate of the range in which 3D‐atmosphere treatment is necessary and where 1D‐atmosphere models suffice for the interpretation of molecular spectral features. This is also important in order to distinguish between the velocity‐broadening and the rotational‐ or Zeeman‐broadening. The synthetic spectra were calculated using 3D CO5BOLD radiative‐hydrodynamic (RHD) models and the line synthesis code LINFOR3D. We used complete 3D‐models and high resolution 3D spectral synthesis for the detailed study of some well isolated FeH lines. The FeH line strength shows a dependence on surface gravity and effective temperature and could be employed to measure both quantities in M‐type objects. The line width is related to the velocity‐field in the model stars, which depends strongly on surface gravit...