SIMBAD references

Subarcsecond (0".75) V and I images have been obtained of 13 new proto-planetary nebulae (PPNs). We find nine of them to be resolved, with sizes up to 3", and two others to perhaps also be extended. Of the nine, four appear to be elliptical in shape. Thus an aspherical morphology is demonstrated to commonly exist early in the transition between the asymptotic giant branch and planetary nebula phases. The results of this larger observational study, together with the previously published imaging studies, indicate that most PPNs are elliptical (or bipolar) in shape.