THE FORMATION OF BINARY AND SINGLE NUCLEI OF PLANETARY-NEBULAE

We model the evolution of binary systems and explore the possibilities of formation of single and binary planetary nebula nuclei (PNNs). Under the assumption that all stars are born in binary systems, we obtain a Galactic rate of PNN formation of 0.87 yr-1. The model suggests that about 20% of all PNNs are single, while 66% are CO white dwarfs accompanied by main-sequence stars. Our results are consistent with the observations of close binary PNNs. However, a direct comparison is difficult due to poor statistics and selection effects which bias the observed sample. We used the obtained results to place constraints on parameters of common envelope evolution. The important role played by binaries in planetary nebula (PN) formation may have important consequences for the luminosity function of PNs. This can have implications for the use of PNs as distance indicators.