SIMBAD references

Monochromatic (Δλ≤10Å) images have been obtained for seven large (2-10 arcmin) Abell planetary nebulae. From this deep survey, we found 4 to have normal bipolar shapes, whereas 3 have truly spherical shells. The structures of these nebulae are discussed using the absolutely calibrated intensity maps in Hα, [N II], and [O III]. An attempt to derive ionized mass using our (dereddened) measured absolute flux as a function of distance to the PN is also given.