Determination of Mass Loss Rates in Central Stars of Planetary Nebulae with the “Sei” Method

Determination of mass loss rates from fast winds in nuclei of planetary nebulae has been extensively performed (Cerruti-Sola and Perinotto, 1985) using low resolution IUE spectra with the method developed by Castor, Lutz and Seaton (1981) (CLS). This method, specially addressed to the analysis of low resolution IUE P Cygni profiles, assumes a given behaviour for the velocity law and for the opacity law in the wind. The second assumption may result in being too severe in specific objects. Moreover other aspects that may affect the line profile as the presence of turbulence across the wind and the correct treatment of doublet lines, are neglected in the CLS study. We have developed a new method, the SEI method, intended to reproduce theoretically the observed single or doublet line profiles under very general physical conditions. We explain the basic aspects of the method and present results obtained from the analysis of IUE high resolution spectra of some central stars of planetary nebulae.