In this paper we presented a grid of spherically symmetric model atmospheres for pre-MS stars. The main change with respect to the NG-giant grid is the use of new TiO and water vapor line lists. In the parameter range considered for the PMS models the changes in the structures of the atmospheres compared to similar models with the NextGen setup are relatively small but the differences of the optical and IR spectra are noticeable. We provide the model structures, spectra and broad-band colors in standard filters through the WWW and anonymous FTP for general use, see http://dilbert.physast.uga.edu/yeti or ftp://calvin.physast.uga.edu/pub/PMS. In a forthcoming paper we will discuss dust formation for cool dwarfs and giants that incorporate the opacities used in this paper, and will explore separately the effects of the present PMS models on evolution tracks for pre-main sequence stars.
This work was supported in part by the CNRS, INSU and by NSF grant AST-9720704, NASA ATP grant NAG 5-8425 and LTSA grant NAG 5-3619, as well as NASA/JPL grant 961582 to the University of Georgia, NASA LTSA grant NAG5-3435 and NASA EPSCoR grant NCCS-168 to Wichita State University. This work was supported in part by the Pôle Scientifique de Modélisation Numérique at ENS-Lyon. Some of the calculations presented in this paper were performed on the CNUSC IBM SP2, the IBM SP2 and SGI Origin 2000 of the UGA UCNS, on the IBM SP of the San Diego Supercomputer Center (SDSC), with support from the National Science Foundation, and on the Cray T3E of the NERSC with support from the DoE. We thank all these institutions for a generous allocation of computer time.