A search for planetary nebulae around hot white dwarfs

We have performed a search for old planetary nebulae around hot white dwarfs by direct Ha narrow-band imaging. The 16 examined objects are white dwarfs representing different spectral subtypes, comprising DA and various non-DA stars, among them being PG 1159 stars and white dwarfs exhibiting spectral signatures of ongoing mass-loss by ultra-hot winds. The search was entirely negative - with one possible exception: PG0109+111, which is the most massive DO white dwarf known (M=0.74 M.) and among the hottest DOs (T-eff=110000 K). An asymmetric nebulosity extends about 5' from the star to the south-west, and there are hints that it extends even further out. If our detection is in fact the first definite case of a PN around a DO white dwarf it needs to be investigated by detailed spectroscopic observations.