Distances to planetary nebulae. I. The reddening-distance method.

Distances to 12 planetary nebulae are derived from the increase of interstellar reddening with distance along the lines of sight of the nebulae. The reddening-distance relations are determined using Walraven VBLUW photometry of stars in small fields around the planetary nebulae. With a theoretical calibration of the VBLUW colors the effective temperature, surface gravity and reddening are determined for early type stars. Distances are then determined by means of a luminosity calibration which is based on the stellar evolution models of Hejlesen (1980). The reddenings of the planetary nebulae are determined using a number of different methods. The amount of internal reddening is estimated. The planetary nebula distances derived from the reddening-distance relations have accuracies of 10 to 40 percent. This is a substantial improvement compared to accuracies of previously determined distances. As a byproduct, the distance to the young open cluster NGC 2453 is determined.