Poster abstract details

To understand the evolution and morphology of planetary nebulae,
a detailed knowledge
of their central stars is required. Among the most interesting objects
are central stars that exhibit emission lines in their spectra,
indicating stellar mass-loss and thus allowing to study the evolution
of planetary nebulae in action. Emission line central stars constitute
about 10\,\% of all central stars. Half of them are practically
hydrogen-free Wolf-Rayet type central stars of the carbon sequence,
so-called [WC] stars,
that show {\em strong} emission lines of carbon and oxygen in their
spectra. Large attention has already been devoted to studies of [WC]
stars and various scenarios of their formation have been proposed.
In this contribution we address the much less studied
{\em weak} emission line central stars (WELS).
These stars are poorly analyzed and their
hydrogen content is mostly unknown. To clarify this situation we
obtained optical spectra, that include the important Balmer lines of
hydrogen, for four weak emission line central stars. We present the
results of our analysis, provide spectral classification and discuss
possible explanations for their formation and evolution.