On the discovery of an enormous ionized halo around the hot DO white dwarf PG 1034+001

The discovery of the largest known planetary nebula on the sky surrounding the DO white dwarf PG 1034+001 with an apparent diameter of about 2°, corresponding to a linear diameter of 3.5-7.0 pc at the likely distance of 100-200 pc, has been reported by Hewett et al. (2003). A careful inspection of available sky survey data has now shown that this planetary nebula, Hewett 1, is surrounded by an elliptical emission shell with an apparent diameter of 6° x 9° (16.2 +6.1 -4.5 x 24.3 +9.1 -6.8 pc at d = 155 +58 -43 pc). A further emission structure, detected northeast of the central star, may indicate another shell with a size of 10° x 16°. From presently available observational data we do not have indications revealing whether the emission arises from material ejected from PG 1034+001 or from ionized ambient ISM. Improved proper motion data combined with radial velocity and distance data from the literature have enabled us to derive a Galactic orbit for the central star PG 1034+001. Its thin disk orbit and the morphology of the first halo suggest that the nebula is in an advanced stage of interaction with the interstellar medium.