For each peculiar galaxy an x-y position in millimeters was recorded,
as measured from the lower-left (south-east) corner of each
plate. These cartesian co-ordinates have been preserved, and are given
with the description of each object in Volume I, along with the plate
and field to which they pertain. These co-ordinates should be
sufficient to locate the object to within a few millimeters. To locate
the same objects on the ESO Quick Blue Survey films, it is necessary
to subtract approximately thirty-five millimeters from both x and y.
Because of uncertainties in the exact centering of the plate at the
telescope and in our measuring devices, it was not possible to produce
precise right ascension and declination co-ordinates from the x-y
co-ordinates directly. Because rotations as well as translations of
the plates with respect to the sky were obviously present in some of
the earliest plates in the survey, (but not in later plates), a single
off-set could not be determined for all of the objects on a given
plate. Instead, individual scaled overlays were prepared for every
object in the Catalogue after rough positions had been derived from
the millimeter positions on the plate. Each object was then
re-examined and corrections to the nominal positions were measured to
an accuracy of fifteen arc seconds. The final positions are given to
the nearest second of time and tenth of a minute of arc. Although
these positions still carry a somewhat optimistic appraisal of the
errors, they are certainly an order of magnitude better than any
derived from the original x-y positions alone.
In some cases the co-ordinates are over-specified. That is, because
of the lack of symmetry of some objects, the ``centre'' is rather
subjective. Additionally, because of the extent of some systems or
because more than one major object is involved in a system, some
visually averaged centre (such as the mid-point between an interacting
double) was chosen which does not necessarily contain any member of
the system. This type of ``centre'' was restricted to systems less than
a few arc minutes in extent. For larger systems, the co-ordinates for
individual members are usually presented. Time constraints precluded
this in some instances, and so readers are strongly advised to
interpret the listed co-ordinates with care, especially when dealing
with multiple systems.
POSITIONS