2 Observations and data reductions

The new velocities presented in this paper have been obtained with the 1.52 m ESO telescope at La Silla (Chile), the 2.0 m telescope at Pic du Midi (France), and with the 1.93 m telescope at Haute-Provence Observatory (France).

Observations with the 1.52 m ESO telescope were carried out in February 1996. We used the Boller and Chivens spectrograph at the Cassegrain focus, equipped with a 600 lines/mm grating blazed at 5000 Å and coupled to an RCA CCD detector ( $1024 \times 640$pixels) with a pixel size of 15 $\mu$m. The dispersion was 172 Å/mm, providing spectral coverage from 3750 to 5700 Å. The exposure times ranged between 30 and 60 min, according to the magnitude of the object. During the run, calibration exposures were made before and after each galaxy observation using an He-Ar source. Observations with the 1.93 m Haute-Provence Observatory telescope were carried out in November 1997, November 1998 and April 2000. We used the CARELEC spectrograph at the Cassegrain focus, equipped with a 150 lines/mm grating blazed at 5000 Å and coupled to an EEV CCD detector (2048$\times$1024 pixels) with a pixel size of 13.5 $\mu$m. The dispersion of 260 Å/mm allowed a spectral coverage from 3600 to 7300 Å. Wavelength calibration was done using exposures of Hg-Ne lamps.

Part of the velocities were obtained during an observing run at the 2.0 m Bernard Lyot telescope at Pic du Midi Observatory in January 1997. Despite the declination of Abell 970, we used the ISARD spectrograph in its long-slit mode with a dispersion of 233 Å/mm with the TEK chip (1024$\times$1024 pixels) of 25 $\mu$m, corresponding to 5.8 Å/pixel. Typically, two exposures of 2700 s each were taken for fields across the cluster. Wavelength calibration was done using Hg-Ne lamps before and after each exposure.

Data reduction was carried out with IRAF using the longslit package. The spectra were rebinned uniformly in log wavelength, with a scale of 1 Å/bin. Radial velocities were determined using the cross-correlation technique (Tonry & Davis 1979) implemented in the RVSAO package (Kurtz et al. 1991; Mink et al. 1995), with radial velocity standards obtained from observations of late-type stars and previously well-studied galaxies.

Table 1 lists positions and heliocentric velocities for 69 individual galaxies in the field of the cluster. The entries in the table are:

1.

identification number;

2.

right ascension (J2000);

3.

declination (J2000);

4.

morphological type determined from a visual inspection of the Palomar sky survey (POSS) images;

5.

$b_{\rm J}$ magnitude from the COSMOS/UKST Southern Sky Object Catalogue;

6.

heliocentric radial velocity with its error (kms^-1);

7.

R-value derived from Tonry & Davis (1979);

8.

telescope and notes- e: 1.52 m ESO telescope, o: 1.93 m OHP telescope; p: 2.0 m Pic du Midi telescope.

For the analysis in the next sections it is important to estimate the completeness level of the velocity sample as a function of the magnitude. To do that (and also to study the cluster galaxy projected distribution) we extracted from the ROE/NRL COSMOS UKST Southern Sky Object Catalogue, supplied by the Anglo-Australian Observatory (Yentis et al. 1992), a sample of galaxies in the direction of the cluster. An examination of Table 1 indicates that, with one exception, all velocities were measured in a region of $\sim$ $27^\prime \times 22^\prime$ (in RA and DEC, respectively), centered on the position of galaxy number 1 in Table 1, which assured a good level of completeness in the core of the cluster. Indeed, by comparing the velocity and the COSMOS catalogues we verify that, within this region, our velocity sample is $\sim$92% complete at $b_{\rm J}^{\rm cosmos}=18$, $\sim$75% at $b_{\rm J}^{\rm cosmos}=19$, and $\sim$51% at $b_{\rm J}^{\rm cosmos} = 19.75$.