SIMBAD references

The determination of reliable distances to planetary nebulae (PNe) is a major difficulty in the study of this class of objects in the Galaxy. The availability of new photometric surveys such as IPHAS (the INT/WFC photometric H_α survey of the northern Galactic plane) covering large portions of the sky provide an opportunity to apply the so-called extinction method to determine the distances of a large number of objects. The technique is applied to a sample of 137 PNe located between -5 and 5 degrees in Galactic latitude, and between 29.52 and 215.49 degrees in longitude. The characteristics of the distance-extinction method and the main sources of errors are carefully discussed. The data on the extinction of the PNe available in the literature, complemented by new observations, allow us to determine extinction distances for 70 PNe. A comparison with statistical distance scales from different authors is presented.