Wind variability in central stars of planetary nebulae. II.

Abstract

New high resolution IUE spectra of central stars of the planetary nebulae (CSPN) NGC 40, NGC 6543, NGC 6826, and BD +30 3639 have been obtained between August 1994 and September 1995 to explore the variability of their P Cygni profiles. The data have been analyzed together with previous observations of the same stars. Significant changes in the profiles of several of the typical wind lines of the N v, O iv, O v, Si iv, C iv, and N iv ions have been revealed in all the observed stars. By combining these results with the ones obtained in a previous paper of this series (\cite[Patriarchi & Perinotto 1995]{Pa95}; Paper I), it is found that half of the fourteen observed CSPN exhibit changes in the shape of their P Cygni profiles up to levels of 10-50% in timescales of years, analogous to similar timescale variations exhibited 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 separated 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 profiles, amount for M_⊙q_NV to a factor of 3 +/- 1.