Self broadening of hydrogen lines: Initial results

For the first time broadening by both resonance and dispersive-inductive interactions with H-atoms are included in the formation of Balmer lines in cool stars, without the use of a multipole expansion. Comparison of synthetic profiles with observed profiles for the Sun and two late F dwarfs shows that this improvement in broadening theory accounts for some of the problems found in previous work. It is anticipated that planned future developments in the theory of self broadening will lead to further improve ments in the modelling of cool star atmospheres

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 components of the interaction (van der Waals forces) have been included, and the resonance components have been computed by perturbation theory without the use of the multipole expansion. The theory is applied to lower Balmer lines and the theoretical and observational impact of the new broadening theory is examined. It is shown that this theory leads to considerable differences in the predicted line profiles in cool stars when compared with previous theories which include only resonance interactions. In particular, the effect is found to be very important in metal poor stars. The theory provides a natural explanation for the behaviour of effective temperatures derived from Balmer lines by others using a theory which includes only resonance broadening. When applied to Balmer lines in the solar spectrum the theory predicts an improved agreement between observed and computed profiles for models which also match limb darkening curves and rules out a model which does not. However significant discrepancies still remain which could be due to inadequacies in our theory or the atmospheric model or both

A list of data for the broadening of metallic lines by neutral hydrogen collisions

A list of data for the broadening by neutral hydrogen collisions of many astrophysically important spectral lines, which has been incorporated into the Vienna Atomic Line Database (VALD), is presented. Data for lines of neutral atoms are interpolated from the tabulated data of Anstee & O'Mara (1995), Barklem & O'Mara (1997), and Barklem et al. (1998). Data for lines of singly ionised atoms are compiled from the calculations by Barklem & O'Mara (1998, 2000). The list at present contains data for 4891 lines between 2300 and 13000 A of elements from Li to Ni. We examine the statistical impact of the new theory by comparison with the previously available data. We also demonstrate the direct eect on spectral synthesis calculations