Introduction

In a recent paper we have presented a grid of spherically symmetric model atmospheres for stars with $\log(g)\leq 3.5$ and in the temperature range $3000\leq \hbox{$\,T_{\rm eff}$} \leq 6800\,{\rm K}$. In this paper, we present an update of the NG-giant grid tuned for young pre-MS (PMS) stars. This PMS grid spans the parameter range $2000\,{\rm K}\leq \hbox{$\,T_{\rm eff}$}\leq 6800\,{\rm K}$ and $2.0 \leq \log(g)\leq 3.5$ for solar abundances. The models were calculated for very low mass stars with $M=0.1\hbox{$\,$M$_\odot$}$ but in the parameter range considered the mass of the star changes the synthetic spectra and the atmospheric structure only marginally. A major difference from our NextGen grids of model atmospheres is the replacement of TiO and H₂O line lists with the newer line list calculated by the NASA-AMES group, for TiO (about 175 million lines of 5 isotopes) and for H₂O (about 350 million lines in 2 isotopes).

In the next section we give a brief overview over the model construction and the differences from the NextGen grids. Then we discuss some results, in particular the effects of the new line lists and we end with a summary of the paper.

for H₂O (about 350 million lines in 2 isotopes).

In the next section we give a brief overview over the model construction and the differences from the NextGen grids. Then we discuss some results, in particular the effects of the new line lists and we end with a summary of the paper.