Binary [WR] and wels central stars of planetary nebulae

A sample of 33 [WR] and wels (weak emission-line central stars) central stars of planetary nebulae was observed in order to search for binary nuclei. One close binary system was discovered. The central star of PN G222.8 - 04.2 is the first [WR] star in a close binary system known, with a period of 0.63 d. The fraction of close binary central stars, leading to photometrical variability, is lower among the hydrogen-poor [WR] stars and wels than among their hydrogen-rich counterparts. This may indicate larger orbital separations or an intrinsically lower binary fraction among [WR] and wels central stars. The detection of one close binary system among the [WR] stars shows that common-envelope evolution does not preclude such stars. It also shows that although a stellar merger is a possible evolutionary channel towards H-poor emission-line stars, it cannot form the only such channel, as PN G222.8 - 04.2 has avoided a merger.