Abell Catalog of Planetary Nebulae
The Abell Catalog of Planetary Nebulae was created in 1966 by George O. Abell and was composed of 86 entries thought to be planetary nebulae that were collected from discoveries, about half by Albert George Wilson and the rest by Abell, Robert George Harrington, and Rudolph Minkowski. All were discovered before August 1955 as part of the National Geographic Society – Palomar Observatory Sky Survey on photographic plates created with the 48-inch (1.2 m) Samuel Oschin telescope at Mount Palomar. Four are better known from previous catalogs: Abell 50 is NGC 6742, Abell 75 is NGC 7076, Abell 37 is IC 972, and Abell 81 is IC 1454. Another four were later rejected as not being planetaries: Abell 11 (reflection nebula), Abell 32 (red plate flaw), Abell 76 (ring galaxy PGC 85185), and Abell 85 (supernova remnant CTB 1 and noted as possibly such in Abell's 1966 paper). Another three were also not included in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (SEC): Abell 9, Abell 17 (red plate flaw), and Abell 64. Planetaries on the list are best viewed with a large aperture telescope (e.g. 18-inch (0.46 m)) and an OIII filter.
- Abell, George O. (1955), "Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey", Publications of the Astronomical Society of the Pacific, 67 (397): 258, Bibcode:1955PASP...67..258A, doi:10.1086/126815,
As the National Geographic Society-Palomar Observatory Sky Survey1 nears completion, preliminary lists are being compiled of some of the many new objects discovered. These lists include more than seventy new planetary nebulae and about a dozen star clusters that are believed to be globular.
- Abell, George O. (April 1966), "Properties of Some Old Planetary Nebulae", Astrophysical Journal, 144: 259, Bibcode:1966ApJ...144..259A, doi:10.1086/148602,
Among the many new objects discovered on the photographs taken for the National Geographic Society-Palomar Observatory Sky Survey, eighty-six provisionally classed as planetary nebulae are described here. A. G. Wilson first identified about half of these objects; the rest were found by R. G. Harrington, R. Minkowski, and the writer. Since the publication of a preliminary finding list of seventy-three of these nebulae (Abell 1955), several more have been discovered; more reliable positions and other data for all of the nebulae are given here. The present list of eighty-six objects includes two entries in the Index Catalogue that were not there-identified as planetary nebulae, five objects in a list of new planetary nebulae that was subsequently published by Kohoutek (1962b, 1963), and at least one object that is a radio source and thus which may be a supernova remnant. All eighty-six objects are included in this investigation, however, and are described as "planetary nebulae," with cognizance of the fact that one or two of them may be improperly identified.
- Acker, A.; Marcout, J.; Ochsenbein, F.; Stenholm, B.; Tylenda, R.; Schohn, C. (1992). "The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae. Parts I, II". The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae. Parts I, II. Garching, Germany: European Southern Observatory (ESO). Bibcode:1992secg.book.....A. ISBN 3-923524-41-2.
The selection of the objects populating this catalogue is mainly based on an observational programme, and a verification programme consisting of spectroscopic observations for all suspected planetary nebulae, assuming that a planetary nebula has a spectral signature which can easy be recognised. For the present catalogue, a list of 1820 objects, each of them called at least once a planetary nebula, have been inspected; 1143 of them have been classified as true or probable planetary nebulae; 347 objects, which status is still unclear, were classified among the "possible" planetary nebulae. Finally, 330 objects have been rejected. Part I: A. Explanation of the catalogue. B. Tables. C. References of papers containing 20 objects or more. D. Finding charts. Part II: The catalogue.
- "The Abell Planetaries".
By "easy" I don't mean easy to see, at least not in a small telescope. (I highly recommend an OIII filter, no matter what size scope you're using.)