When Vincent Reddish was appointed by the United Kingdom Science
Research Council (SRC) to plan and build the 48-inch Schmidt telescope
in Australia, it was clear that a major opportunity would be created
to discover new astronomical objects and phenomena in the relatively
little-explored southern hemisphere. One of the first programmes to be
undertaken on the telescope would be a systematic survey of the whole
southern sky. This project was part of the ESO/SRC Southern Sky Survey
and was one of the responsibilities of the United Kingdom Schmidt
Telescope Unit. The prototype telescope for the UK Schmidt was the
48-inch Schmidt on Palomar Mountain which, in the 1950's, had produced
the famous and widely used sky survey of the northern hemisphere. The
Schmidt in Australia was to utilize the new Eastman Kodak IIIa-J
emulsion, which, together with the fast (f/2.5) optics and the dark
skies at Siding Spring, would penetrate to fainter magnitudes than had
ever before been systematically observed in either hemisphere.
Early in 1973 Reddish decided that the many new and interesting
objects in the southern sky survey should be systematically recorded
and published. To that end he invited Arp to Edinburgh to consider the
production of a catalogue of the objects then appearing on the first
of these survey plates.
Arp (1966)
had previously published the Atlas
of Peculiar Galaxies: 333 unusual objects in the northern hemisphere
discovered on the Palomar Sky Survey by astronomers such as himself,
Vorontsov-Velyaminov, A. Wilson, F. Zwicky and others. Arp realized
that the deep U.K. Schmidt Survey would detect low-surface-brightness
features better than any previous survey and would therefore register
much larger extensions around the outer edges of galaxies. He felt
that these faint outer regions would reveal pecularities of a kind not
ordinarily visible and demonstrate associations between objects not
normally suspected of being associated. Therefore he enthusiastically
began the project on his own in 1973.
After the first session of examining plates it became clear that
thoroughly searching all the plates in the southern hemisphere survey
was a formidable task for one person. In the fall of 1974, to
alleviate the situation Reddish sought participation from some of the
other astronomy centres in Britain. As a result of this invitation
Donald Lynden-Bell proposed to Barry Madore, then in Cambridge, that
he join the project. Madore accepted, and in November 1974 Arp and
Madore searched the first set of plates together in Edinburgh. This
collaboration was to last more than ten years.
During the first seven years Arp and Madore made visits about once a
year to Edinburgh to search each batch of new plates which had been
obtained in Australia and shipped to Scotland. At first, each plate
took a considerable time to scan; inspecting every galaxy down to a
size limit of about 0.2 millimeter (=10 arcsec) is by no means a
trivial task. But gradually, as facility was developed, the
plate-scanning speed rose from an average of two per day to about
six. Still, even with this improvement the decision was made to limit
the Catalogue to zones only as far north as a declination centre of
-25 degrees. Therefore the Catalogue is a complete listing of peculiar
objects from the south celestial pole to a declination of -22
degrees. There are 537 plates, nominally 6.5 degrees by 6.5 degrees
square, comprising the SRC Sky Survey coverage of this area in the
southern sky.
During all these years the whole staff of the U.K. Schmidt Telescope
Unit were enormously helpful. Russell Cannon and Tim Hawarden took the
responsibility of setting up plate-scanning and measuring facilities.
Russell Eberst and Elizabeth Sim helped to locate the best available
plates on which to carry out the survey. When the last plate was
scanned in the fall of 1980 the work of collating the tabular
descriptions and positions of some seven thousand objects, and
producing the photographs of about a sixth of these, was started. It
was decided to produce two volumes. The first, containing positions
and descriptions for all peculiar objects, would be the quantitative
basis for future studies. The second, containing selected
photographs, would illustrate the various categories of peculiarity
and bring attention to the outstanding members of each category.
Because some of the survey plate centres did not coincide exactly
with the nominal centres, some of the early positions of particular
objects were inaccurate. It was therefore decided that the positions
of all objects should be checked by overlays. In 1980 Petrusia
Bojetchko and Ed Anderson spent part of a summer in Toronto correcting
positions; and in 1981 Matthew Bates extended the work in a one-month
stay at Edinburgh. It later became clear, however, that some of the
simple procedures adopted for correcting the co-ordinates were
inadequate and so during 1982/83 Madore and Robert Freedman repeated
the overlays and off-sets for the entire Catalogue.
This re-analysis was almost as time consuming as the original search
and delayed the publication considerably. But it was essential. The
pointing accuracy of most large optical telescopes is now better than
a few tenths of an arcmin, and accordingly the TV acquisition finder
fields are usually only a minute or two in diameter. If the Catalogue
was to serve the practical needs of optical astronomers, the
co-ordinates had to be determined to better than the one arc minute
accuracy obtained for the first rough reductions. Other catalogues
were to be cross-referenced with our Catalogue, thus good positions
were essential in eliminating confusion at a later date. Finally,
since the names of the objects were to consist of the truncated
co-ordinates (the so-called Parkes nomenclature) the derived
co-ordinates had to be correct to the limits of the truncation.
The co-ordinate revision also provided unexpected benefits. Because
the off-sets were generally made using copies of plates that were not
those originally surveyed, ambiguities caused by plate defects were
resolved (for instance, ``dwarf/defect?'' classifications were usually
decided by the second plate). Every classification was in this way
verified for at least a third time after a considerable period. Very
occasionally, a new object was included in the sample if it were of
sufficient interest. Although this type of inclusion was not to be
desired for reasons of uniformity, it was usually only made for dwarf
and compact galaxies which have an intrinsically uncertain discovery
rate.
It was decided that in the case of well-separated associations of
objects, every effort would be made to assign individual names and
positions to the prominent members, while preserving the nature of the
association in the description and code. Often it is by no means clear
what single co-ordinate should apply to groupings: frequently no
single member is dominant, and in the case of pairs, for instance, the
midpoint contains neither member. This latter situation was seen as
potentially leading to problems in TV acquisition and
cross-referencing with other catalogues. Still, because of the numbers
involved in such groupings, some practical limit to this process had
to be imposed. Thus, for systems less than a few minutes in total
extent, or for larger systems in which there is an obvious and
dominant centre of symmetry, only one co-ordinate is listed. For
larger and for more irregular systems with less than half a dozen
dominant members, individual co-ordinates were obtained. We trust that
the effort required in making these modifications and extensions will
make the Catalogue both a practical and long-lived tool despite the
resulting delays.
By the end of 1980, the volume of photographic reproductions was
also ready to be prepared. The thousand photographs which were
scheduled for publication represented a major undertaking for the ROE
Photographic Laboratory. Careful consultation with the head of that
laboratory, Brian Hadley, produced a plan for the production of
standard sizes and formats for the photographs. Two test runs were
made in order to set the optimal contrast and density for the
prints. For the final production, Russell Eberst of the Schmidt Unit
identified each object on the best available plate or film and marked
the area to be photographed. The successful completion of this phase
owes much to the good judgement in identification and framing which
Eberst made on this long list of objects. Lastly, Bill Roberton of the
ROE Photographic Laboratory produced all the final prints. The superb
quality of the final prints is a tribute to Roberton's skill and
diligence.
During this period, Malcolm Longair assumed the Directorship of ROE.
In spite of his many new duties in the vigorous research activities at
ROE he found time to see that the grant given by the SRC for the
completion of the Catalogue was maintained. He consulted and advised
in the publication of the Catalogue, and the whole of the Observatory
staff helped with suggestions and criticism of the final edition.
PREFACE