Planetary nebulae survey and outlook

The planetary nebula NGC 6826

“…He also lists four objects of the "giant halo" type NGC 6543, NGC 6826, NGC 6891, and IC 4593) to which Terzian (1980) added two more (He 2-111 and NGC 6853), but did not include, NGC 6826 in the list of triple-shell objects and quotes only the two listed by Kaler. The problem of multiple-shell formation has been addressed by Aller (1976) and by Mathews (1978), and the dynamics of envelopes have been treated by Wentzel (1976).…”

The PN 164+31 1.

“…The nebula exhibits very weak hydrogen lines with the Ha much weaker than (Aller 1976). Finally, the weakness of the hydrogen lines relative to [O III] suggest a moderate excitation in agreement with Doroshenko and Kolotilov (1973).…”

“…1, in the Catalog of Perek and Kohoutek (1967) is frequently misidentified as NGC 2474/75. The misidentification originated in a paper by Jones and Emberson (1939) and has occurred subsequently in many references (Perek and Kohoutek 1967;Gurzadyan 1969;Aller 1970;Higgs 1971;Doroshenko and Kolotilov 1973). The misidentification was not made in a photograph of 164 + 31?1 given by Minkowski and Aller (1954).…”