We have observed at the 3.6 m Canada-France-Hawaii Telescope during four
nights in May 1993 with the MOS-SIS spectrograph (Le Fèvre et al.
1994) in the imaging mode.
The Loral3 CCD, which
has a 2048 
2048 pixel format, provides images of 9.7 
9.4
arcmin
(after discarding the vignetting area) - at the distance of the
Coma cluster, 10 arcmin correspond to 0.4 
Mpc - and the pixel
size is 0.3145 arcsec.
A ``mosaic'' of 21 overlapping images in the V-band was thus obtained
covering a total field of
about 0.4 degrees
centered on the two brightest central galaxies
of Coma (NGC 4874 and NGC 4889). An additional frame was taken of the
south-west NGC 4839 group. In Fig. 1 (click here) we display the observed regions.
The exposure time for each image was 3 minutes.
Flat-field frames of the twilight sky were also obtained with 1 second
exposure time each, as well as a standard star calibration field in M 92
with a 90 second exposure. During the whole run the seeing (as
estimated by the point spread function of stars in the images) varied from
0.9 to 1.4 arcsec.
Figure 1: Map of the observed areas. Dots indicate the
positions of the giant
galaxies NGC 4874 and NGC 4889 in the centre, and NGC 4839 in the south-west
frame. Coordinates are given relatively to the GMP centre - see
Sect. 5 (click here) - located at 
,
(1950.0). North is up, east is to the left
Figure 2: Normalized compactness parameter Q vs. isophotal magnitude for all
observed objects. The dashed line indicates the 
value
determined
to separate stars (below the line) from galaxies (above the line)
Figure 3: Histogram of magnitudes for raw galaxy counts. The turnover of
the histogram, around 
, gives an estimate of the
completeness magnitude of the observations. Poisson error bars are
displayed
Figure 4: Central surface brightness plotted against isophotal magnitudes for
all the catalogued galaxies. The dashed line indicates the completeness
magnitude limit