2 Observations

2.1 Schmidt plates

In the framework of a recent supernova search program (Meusinger & Brunzendorf [1996]; Meusinger et al. [1999a]), 30 plates have been taken with the Tautenburg 2m telescope in its Schmidt mode (134cm free aperture, 4m focal length) between September 1992 and March 1995. These plates provide, in combination with 7 older archive plates, the major part of the observational material for the present study (Table 1). The plate emulsions Kodak 103a-O as well as the similar ORWO AS and ORWO ZU21 are sensitive in the blue spectral range. In combination with a Schott GG13 filter, they closely match the Johnson B band.

  

Table 1: Summary of observations

¹Numbers of plates selected for photometry and/or astrometry are printed italic. ²No filter used.

The plates cover an unvignetted area of $3\hbox{$.\!\!^\circ$}3\times3\hbox{$.\!\!^\circ$}3$ around the centre of the Perseus cluster at a scale of 51.4arcsecmm^-1. With a typical exposure time of 30min (22-60min), the mean limiting magnitude is $B \approx 20$. The deepest plates have limits of $B \approx 21.5$.The mean seeing conditions were rather poor (2''-3''). This is, however, not critical for the investigation of extended features in galaxies. On the other hand, the brighter fine structures, especially in the central regions of galaxies, can be studied well on those few plates taken under good seeing conditions ($\approx 1''$). Almost every plate (except the oldest ones) has a calibration wedge in its northwestern corner.

2.2 Low-dispersion spectroscopy

Comprehensive radial velocity data are important in galaxy cluster studies in several respects. Our work, however, is not focused on a substantial enlargement of the radial velocity data base. Nonetheless, we were interested in further radial velocity measurements in the context of two particular issues: the substructure in the projected galaxy distribution $1\hbox{$.\!\!^\circ$}5$ north of the cluster centre (see Sect.7.1) and the properties of the IRAS galaxies in the field (Meusinger & Brunzendorf, in preparation). In the framework of the follow-up spectroscopy of QSO candidates in a different field (Meusinger et al. [1999b]) we were in the position to use some observing time during the dawn for obtaining several low-dispersion spectra for five galaxies from our catalogue, namely two IRAS galaxies (342, 540) and three galaxies from the clump north of the cluster centre (329, 335, 353). The observations were taken on July 26 and 27, 1998 with CAFOS at the 2.2m telescope on Calar Alto, Spain, equipped with the B-400 grism and a SITe1d CCD. A slit of $1\hbox{$.\!\!^{\prime\prime}$}2$ (July 26) or $1\hbox{$.\!\!^{\prime\prime}$}6$ (July 27) yielded a resolution of about 20 or 30Å, respectively. Two spectra were obtained for each galaxy with total exposure times between 370s and 600s.