SPHERICAL OPACITY SAMPLING MODEL ATMOSPHERES FOR M-GIANTS .1. TECHNIQUES, DATA AND DISCUSSION

We present a new code for the calculation of static, spherically symme tric, opacity sampling model atmospheres in local thermodynamic equili brium for cool giants and supergiants of spectral type M. Up-to-date d ata for line opacities have been included, with new calculated line li sts for the TiO, VO and H2O molecules. This is the first time both sph ericity and a realistic description (opacity sampling) of all opacity sources are used simultaneously for the calculation of cool stellar at mospheres and this results in a better agreement between calculated an d observed fluxes and colours. A grid of models covering 3000 K less-t han-or-equal-to T(eff) less-than-or-equal-to 4000 K, -0.5 less-than-or -equal-to log g less-than-or-equal-to 1.5 for 1M. less-than-or-equal-t o M less-than-or-equal-to 5M. with solar composition will be published separately.