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New high resolution IUE spectra of cen- tral stars of the planetary nebulae (CSPN) NGC 40, NGC 6543, NGC 6826, and BD +30 3639 have been ob- tained between August 1994 and September 1995 to ex- plore the variability of their P Cygni proles. The data have been analyzed together with previous observations of the same stars. Signicant changes in the proles of several of the typical wind lines of the N v ,O iv ,O v , Si iv ,C iv ,a nd Niv ions have been revealed in all the observed stars. By combining these results with the ones obtained in a previous paper of this series (Patriarchi & Perinotto 1995; Paper I), it is found that half of the four- teen observed CSPN exhibit changes in the shape of their P Cygni proles up to levels of 10 50% in timescales of years, analogous to similar timescale variations exhib- ited by hot stars of population I. They are: NGC 40, NGC 1535, NGC 2392, NGC 6543, NGC 6826, IC 4593 and BD + 30 3639. The ones for which changes have not been detected are: NGC 246, NGC 6210, NGC 6572, NGC 7009, IC 418, IC 2149 and Lo 8. The present paper completes the survey of this type (at least 2 3 well sep- arated high resolution good exposures for each star) that could have been done in central stars of planetary nebulae using the IUE satellite. In a typical case (NGC 1535) we estimate that the changes in the physical properties of the wind, resulting from the observed changes in the P Cygni proles, amount for _ MqNV to a factor of 3 1.

Wind variability in central stars of planetary nebulae. II.