  We report on radiative hydrodynamic simulations of M dwarf stellar flares and
compare the model predictions to observations of several flares. The flares
were simulated by calculating the hydrodynamic response of a model M dwarf
atmosphere to a beam of non-thermal electrons. Radiative backwarming through
numerous soft X-ray, extreme ultraviolet, and ultraviolet transitions are also
included. The equations of radiative transfer and statistical equilibrium are
treated in non-LTE for many transitions of hydrogen, helium and the Ca II ion
allowing the calculation of detailed line profiles and continuum radiation. Two
simulations were carried out, with electron beam fluxes corresponding to
moderate and strong beam heating. In both cases we find the dynamics can be
naturally divided into two phases: an initial gentle phase in which hydrogen
and helium radiate away much of the beam energy, and an explosive phase
characterized by large hydrodynamic waves. During the initial phase, lower
chromospheric material is evaporated into higher regions of the atmosphere
causing many lines and continua to brighten dramatically. The He II Lya line is
especially enhanced, becoming the brightest line in the flaring spectrum. The
hydrogen Balmer lines also become much brighter and show very broad line
widths, in agreement with observations. We compare our predicted Balmer
decrements to decrements calculated for several flare observations and find the
predictions to be in general agreement with the observations. During the
explosive phase both condensation and evaporation waves are produced. The
moderate flare simulation predicts a peak evaporation wave of 130 km/s and a
condensation wave of 30 km/s. The velocity of the condensation wave matches
velocities observed in several transition region lines.
