Self-broadening in Balmer line wing formation in stellar atmospheres

Details of a theory of self-broadening of hydrogen lines are presented. The main features of the new theory are that the dispersive-inductive componen ts of the interaction (van der Waals forces) have been included, and the re sonance components have been computed by perturbation theory without the us e of the multipole expansion. The theory is applied to lower Balmer lines a nd the theoretical and observational impact of the new broadening theory is examined. It is shown that this theory leads to considerable differences i n the predicted line profiles in cool stars when compared with previous the ories which include only resonance interactions. In particular, the effect is found to be very important in metal poor stars. The theory provides a na tural explanation for the behaviour of effective temperatures derived from Balmer lines by others using a theory which includes only resonance broaden ing. When applied to Balmer lines in the solar spectrum the theory predicts an improved agreement between observed and computed profiles for models wh ich also match limb darkening curves and rules out a model which does not. However significant discrepancies still remain which could be due to inadeq uacies in our theory or the atmospheric model or both.