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Up: A photometric catalogue

1. Observations

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 tex2html_wrap_inline952 2048 pixel format, provides images of 9.7 tex2html_wrap_inline954 9.4  arcmintex2html_wrap_inline956 (after discarding the vignetting area) - at the distance of the Coma cluster, 10 arcmin correspond to 0.4 tex2html_wrap_inline958 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 degreestex2html_wrap_inline962 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 tex2html_wrap_inline964, tex2html_wrap_inline966 (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 tex2html_wrap_inline970 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 tex2html_wrap_inline972, 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

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Up: A photometric catalogue

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