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

The T(eff) (effective temperature) scale for M dwarfs is very uncertai n. One method which can be used to establish this scale is to compare observed spectra to synthetic ones derived from appropriate model atmo spheres. With this method the adequacy of the model atmosphere is of g reat importance and simple models can give incorrect results. Alternat ively if the T(eff) scale is known with some accuracy then this compar ison is a good test of the adequacy of the models. We have computed so me new and preliminary model atmospheres for late type dwarfs which ac curately treat the line opacity with the opacity sampling technique an d employ laboratory values for the transition strengths of molecular b ands. 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 accept ed T(eff) scale for early M dwarfs with the models suggesting values s ome 200 K hotter.