Planetary Nebulae (PNe) are highly representative of the last stages of intermediate mass stellar evolution. However, there are still many unresolved questions concerning their evolutionary scheme. Mass loss processes during the Asymptotic Giant Branch (AGB) are not fully understood. Binarity, rotation and magnetic fields may play an important role

Erratum to Astron. Astrophys. Suppl. Ser. 117 (1996) 227-254.

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We report the variations of the UV spectrum of BP Tau from 5 to 19 January, 1992 when the star was monitored with IUE during 2 rotation periods. Our data indicate that lines that can be excited by recombination processes, such as those from O I and He II have periodic-like light curves, whereas lines that are only collisionally excited do not