MODEL ATMOSPHERES AND THE T(EFF) SCALE FOR M-DWARFS

The T(eff) (effective temperature) scale for M dwarfs is very uncertain. One method which can be used to establish this scale is to compare observed spectra to synthetic ones derived from appropriate model atmospheres. With this method the adequacy of the model atmosphere is of great importance and simple models can give incorrect results. Alternatively if the T(eff) scale is known with some accuracy then this comparison is a good test of the adequacy of the models. We have computed some new and preliminary model atmospheres for late type dwarfs which accurately treat the line opacity with the opacity sampling technique and employ laboratory values for the transition strengths of molecular bands. With the above two considerations in mind we compare the fluxes of these models to observed fluxes of late K and early M dwarfs. This preliminary analysis indicates a discrepancy with the currently accepted T(eff) scale for early M dwarfs with the models suggesting values some 200 K hotter.