Wind variability in central stars of planetary nebulae. II.

¹ GNA/CNR, c/o Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
² Dipartimento di Astronomia e Scienza dello Spazio, Universitá di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy

Send offprint request to: M. Perinotto

Received: 14 May 1996
Accepted: 8 April 1997

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 (Patriarchi & Perinotto 1995; 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 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  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 to a factor of .