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Astron. Astrophys. 356, 815-826 (2000)

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2. The data

2.1. Optical data

Our redshift catalogue includes 466 galaxies in the direction of the cluster Abell 496, in a region covering about 160[FORMULA]160 arcmin2 (9.2[FORMULA]9.2 Mpc for an average redshift for Abell 496 of 0.0331). It is fully described in Durret et al. (1999b).

Our photometric catalogues are described in Slezak et al. (1999). The photographic plate catalogue was obtained by scanning an SRC plate in the b[FORMULA] band with the MAMA measuring machine at the Observatoire de Paris; it includes 3879 galaxies located in a region of roughly [FORMULA] 1.3o from the cluster centre. Positions are very accurate in this catalogue and were used for spectroscopy; on the other hand, b[FORMULA] magnitudes are not accurate, so a CCD photometric catalogue was obtained in the V and R bands in order to recalibrate photographic plate magnitudes. The R magnitudes thus estimated for the photographic plate catalogue were used to estimate the completeness of our redshift catalogue. The CCD imaging catalogue includes 239 and 610 galaxies in the V and R bands respectively, and is limited to a much smaller region of [FORMULA] arcmin2 in the centre of the cluster.

The cluster center will be taken to be the position of the cD galaxy, which coincides with the X-ray maximum: [FORMULA] (2000.0).

2.2. X-ray data

The ROSAT PSPC image (#800024) was taken from the archive and analyzed by Pislar (1998). The cluster was observed during 8972 s. The effective exposure time for this image, after data reduction is 5354 s. We have used the routines developed by Snowden (1995) to obtain a non cosmic background subtracted image between 0.5 and 2 keV. We have defined the image limiting radius ([FORMULA] kpc) as the radius where the surface brightness reaches the surface brightness of the cosmic background ([FORMULA]). The different PSPC background components are detailed in Snowden et al. (1994).

The global X-ray gas temperatures derived from Einstein and EXOSAT satellite data are 3.9[FORMULA]0.2 keV (David et al. 1993) and [FORMULA] keV respectively (Edge & Stewart 1991).

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© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000