TiO and H2O absorption lines in cool stellar atmospheres

Over the past decade, model atmospheres and synthetic spectra for late-type stars have improved hand-in-hand with higher quality opacities. In 1994, quality lists of transitions of the water vapor molecule based on ab initio molecular calculations became available (Miller et al. 1994; Schryber, Miller, & Tennyson 1995; Jørgensen, Jensen, & Sørensen 1994) which allowed the computation of the first Direct Opacity Sampling (hereafter dOS) model atmospheres for late-type dwarfs (Allard et al. 1994) and brown dwarfs (Allard et al. 1996), later to become the NextGen models described in (Hauschildt, Allard, & Baron 1999). Showing a more physical description of their main opacities, the NextGen dOS model atmospheres promised a better description of the Spectral Energy Distribution (hereafter SED) of cool stars. And this appeared to be verified for the infrared SED of M dwarfs (Jones et al. 1996; Leggett et al. 1996; Allard et al. 1997).