2 Observations

The totality of these observations has been carried out with the meridian-transit Nançay radiotelescope (France). This instrument is a single dish antenna with a collecting area of 6912 m² (200 $\times$ 34.56) equivalent to that of a 94 m-diameter parabolic dish. The half-power beam width at 21-cm is 3.6 arcmin (EW) $\times$ 22 arcmin (NS) (at zero declination). The minimal system temperature at $\delta = 15^{\circ}$ is about 37 K in both horizontal and vertical polarizations. The spectrometer is a 1024-channel autocorrelator of 6.4 MHz bandwidth. The spacing of the channels corresponds to 2.6 km s^-1 at 21 cm with a bank of 512 channels in each polarization. After boxcar smoothing the final resolution is typically 10 km s^-1. In the velocity-search mode the 1024 channels are split in four banks of 256 channels leading to a range of 4800 km s^-1 (generally from 400 to 5200 km s^-1 or from 5200 to 10000 km s^-1). The gain of the antenna has been calibrated according to Fouqué et al. 1990; the final HI-fluxes (Table 7) are expressed by using as reference a set of 9 calibrator galaxies regularly observed since 1988 (see Sect. 6).

We used the Nançay processing package SIR (Système Interactif de Réduction). The processing chain consist of a selection of good observation cycles (one "observation" is a series of on/off observational sequences), the straightening of the base-line by a polynomial fit, and the application of a boxcar smoothing. The maximum of the line is determined by eye as the mean value of the maxima of each profile's horn after taking into account the medium noise (evaluated in the base-line). The widths, measured at the standard levels 20% and 50% of that maximum, correspond to the "distance" separating the two external points of the profile at these intensity levels.

The total list of corrected HI-astrophysical parameters (Table 7), 21-cm line profiles (Fig. 5), and their corresponding comments (Appendix A and B), is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html or via http://www.edpsciences.com. As an example, the first page of Table 2 and Fig. 5 are presented at the end of this paper.