Up: A visual survey for
A total of 19 POSSII R film copies, each comprising a
field size of about 40 square degrees,
were scanned. The longitude range selected was
and in this interval all fields with
centers at
were examined. Table 1 displays the list of
fields.
The main reasons for selecting this longitude range were:
- 1.
- The Supergalactic Plane crosses the Galactic Plane at
. The significance to probe the ZOA in a wide
strip around this longitude is obvious - and is indicated by the
fact that several bright galaxies (e.g. Maffei1 and 2, IC 342)
lie behind the galactic plane.
- 2.
- Beginning with
, the surface density of
galaxies in the ZOA sharply increases (Weinberger 1980) and the handling of
data is thus made considerably more difficult; fortunately, a large
set of data in the anticenter ZOA based on inspection of POSSI
red-sensitive plates already exists (Pantoja 1995; Seeberger et al. 1996; Saurer et al. 1997).
Table 1:
The fields of POSSII searched for our program
|
In an earlier paper (Seeberger et al. 1996) we have argued that red-sensitive surveys
are the most suitable material for galaxy searches in the ZOA - hence our
selection of the POSSII R films. The visual examination was done by one of us
(MG) and a check of all objects together with the decision to finally
accept or reject an object was done by RW. Individual films were scanned
along overlapping strips of about 1 cm wide by use of a microscope at
16
magnification.
Typically a film copy
took about ten to twelve
hours to scan.
Equatorial coordinates were determined using
a high-resolution digitizer and a suitable software developed at Innsbruck.
The overall accuracy is about
. Diameters
of each galaxy candidate were determined using the microscope
at 25
magnification and a glass plate with a 0.1mm grating;
e.g., the major-axis diameter is defined as the maximum extent of the galaxy
as seen by the eye through the microscope and is specified in increments
of 0
(however, the diameters are not this accurate - about
is probably more appropriate).
Up: A visual survey for
Copyright The European Southern Observatory (ESO)