Abell Catalogue - The Southern Survey

The Southern Survey

The sky-coverage of the 1958 catalog was limited to declinations north of –27°, the original southern limit of POSS. To rectify this and other shortcomings, the original catalog was later revised and supplemented with an additional catalog – the “Southern Survey” – of rich galaxy clusters from those parts of the south celestial hemisphere that had been omitted from the original catalog.

The Southern Survey added a further 1,361 rich clusters to Abell’s original Northern Survey. The deep IIIa-J plates of the Southern Sky Survey (SSS) were used in the survey. These photographic plates were taken with the United Kingdom’s 1.2-metre Schmidt Telescope at Siding Spring Observatory, Australia, in the 1970s. Abell began the survey during a sabbatical year in Edinburgh in 1976. There he enlisted the assistance of Harold G Corwin of the University of Edinburgh, who continued to work on the catalog until 1981, at which time he joined the Department of Astronomy at the University of Texas. By then about half the survey had been completed. An interim paper on the Southern Survey was read at a symposium in 1983, about one month before Abell’s death; the catalog was completed by Ronald P Olowin of the University of Oklahoma, and published in 1989.

Abell and Corwin worked from original plates stored at the Royal Observatory in Edinburgh, scanning the plates visually with a 3x wide-angle magnifier; Olowin used high-quality film copies, which he scanned both visually with a 7x magnifying lens and automatically with a backlit digitizer.

The criteria for inclusion in Abell’s Northern Survey were retained, as were Abell’s “richness” and “distance” classifications – but with the distance classes now being defined in terms of redshift rather than magnitude. As before, clusters were included if they had at least thirty bright galaxies, as it was estimated that this would all but eliminate the possibility of genuinely rich clusters (i.e. clusters with at least fifty bright members) being omitted. The Southern Survey retains the system of designation devised by Abell for his original catalog, with the numbers running from 2713 to 4076. (The catalog contains three duplicate entries: A3208 = A3207, A3833 = A3832, and A3897 = A2462.) The equatorial co-ordinates are for the equinoxes 1950 and 2000, while the galactic co-ordinates are calculated from the 1950 equatorial co-ordinates.

Abell’s original catalog – revised, corrected and updated – was included in the 1989 paper, as was the Abell Supplement, a supplementary catalog of 1,174 clusters from the Southern Survey which were not rich enough or were too distant to be included in the main catalog.