SIMBAD references

The distances D of planetary nebulae (PNe) are still extremely uncertain. Although a variety of methods have been used to evaluate this parameter, these are often in conflict, and subject to large random and systematic errors. It is therefore important to evaluate D using as many independent procedures as possible. We outline here one further way in which this parameter may be assessed. It is noted that where the nebular mass range is narrow, then one might expect observed PNe radii to be roughly similar. This, where it occurs, would also result in a correlation between their angular diameters Theta, and distances D. We find that just such a trend occurs for Type I nebulae, and we employ this to determine distances to a further 44 such outflows. Our mean values of D appear similar to those of Zhang [ApJS 98 (1995) 659], implying a relatively long PNe distance scale.