TiO and H2O Absorption Lines in Cool Stellar Atmospheres

We compare the structures of model atmospheres and synthetic spectracalculated using different line lists for TiO and water vapor. We discuss theeffects of different line list combinations on the model strutures and spectrafor both dwarf and giant stars. It is shown that recent improvements result insignificantly improved spectra, in particular in the optical where TiO bandsare important. The water vapor dominated near-IR region remains problematic asthe current water line lists do not yet completely reproduce the shapes of theobserved spectra. We find that the AMES TiO list provides more opacity in mostbands and that the new, smaller oscillator strengths lead to systematicallycooler temperatures for early type M dwarfs than previous models. These effectscombine and will help to siginificantly improve the fits of models toobservations in the optical as well as result in improved synthetic photometryof M stars. We show that the Davis 1986 \fel-values for the $\delta$ and $\phi$bands of TiO best reproduce the observed (V-I) color indices.Comment: ApJ, in press. Also available at ftp://calvin.physast.uga.edu/pub/preprint