METAL-POOR PLANETARY-NEBULAE - EFFECTS OF WINDS

Some planetary nebulae in the galactic thick disk display extremely lo w abundances of heavy elements such as O, Ne, S, and Ar, compared with ''normal'' or type II nebulae. Their central stars are generally rela tively cool and underluminous, indicating that the progenitor stars ha d very low masses. It is suggested that strong stellar winds have had an important role in the formation of these objects, which is supporte d by the large mass loss rates now observed.