SIMBAD references

The results of a systematic investigation of ion-dynamical effects on the Stark broadening of hydrogen and single ionized helium are reported. This investigation was motivated by the Balmer line problem present for the analysis of hydrogen-rich central stars of old planetary nebulae (PN) and related objects: very different temperatures are derived from the fit of different Balmer lines. The Balmer line problem and several possible reasons are discussed in detail. After discarding all other considered reasons ion-dynamical effects remain as the most likely explanation. Therefore these effects were examined in detail. Line profiles with the inclusion of ion-dynamics were computed according to the approximate method presented by Schoening (1993). An extensive grid of model atmospheres representative for the whole range of hot stars was calculated. Several atmospheric compositions from pure hydrogen to helium-dominated were considered. Although it is demonstrated by Schoening (1993) that differences between line profiles calculated with and without the inclusion of ion-dynamical effects are large (up to some 10%), the resulting changes in stellar profiles of the Balmer lines are very small and can be neglected for practical purposes. More pronounced are changes in the line profiles of the HeII 4686A line. However, even these differences are small and do not cause important changes in derived parameters. Hence it follows that ion-dynamical effects cannot solve the Balmer line problem. In the moment therefore a plausible explanation is still lacking for this problem.