Extinction Distances: Partly New Access to an Old Problem

Abstract

The distance determination to planetary nebulae (PNe) remains a serious problem as illustrated during the last IAU symposium in 1991 (Terzian, IAU 155, p. 109). Since then the situation has not improved significantly. The number of stars for which reddening and spectral data are available, though, has increased tremendously over the last decade. Using data from the literature we have determined extinction distances for more than 50 PNe. The extinction distance method has been pioneered by Lutz (ApJ 181, 135 (1973)) and Acker (A&AS 33, 367 (1978)). The basic assumption of the extinction method is that a reddening vs distance relation (RDR) exists along the line of sight to a given object. Once this relation and the reddening of the object itself is known, a distance to the object can be derived. Gathier et al. (A&A 157, 171 (1986)) present a thorough discussion of the advantages and possible problems of the method. The most recent contributions are by Martin (A&A 281, 526 (1994)) and Saurer (A&A 297, 261 (1995)).