We have also benefited from images of much better resolution, kindly communicated to us by D. Bettoni (for HCG 67), and by P. Hickson (for all three groups); hereafter, these R-band frames will be referred to as DB-Asiago and PH-CFHT images, respectively.
|member||exp. time||slit PA||seeing FWHM|
|HCG 67a||13 49 11.3||-7 13 27.6||37||2.7|
|HCG 67d||13 49 09.7||-7 13 54.3||37||2.7|
|HCG 74a||15 19 24.7||21 06 20.3||21||2.1|
|HCG 74b||15 19 24.4||20 53 23.4||21||2.1|
|HCG 79a||15 59 11.4||20 45 14.9||65||2.9|
|HCG 79b||15 59 12.6||20 45 47.1||79||2.9|
|HCG 79c||15 59 10.9||20 45 41.4||79||2.9|
We have followed closely the technique used in Simien & Prugniel ([1997a], [1997b], [1997c], ), whose main characteristics are summarized again, for convenience. Pre-reduction, cosmic-ray removal in the outer regions, wavelength calibration and sky subtraction were performed with ESO-MIDAS. Multiple spectra of the same object were co-added after applying a proper relative shift, i.e.: a) in , using the calibration spectra to monitor the mechanical flexures within the spectrograph, and b) perpendicularly to the dispersion, to match the nucleus position along the slit, down to a fraction of pixel.
The kinematical parameters are determined by a Fourier-Fitting technique similar to that described in Franx et al. (). This allows the simultaneous calculation of the rotation velocity V(r) and the velocity dispersion , as a function of the distance r from the center.
The removal of the cosmic-ray hits in the central regions is performed on the galaxy spectrum within the same procedure; it is based on a three-sigma clipping of residuals between the galaxy spectrum and the properly shifted, convolved star spectrum. The V and parameters are actually determined in two successive steps, using first the raw galaxy spectrum, and then the spectrum with cosmic rays removed as explained. Adjacent lines are averaged to enhance the S/N ratio of the spectrum in the outer regions. For a spectrum at radius r, a weight is assigned to the neighboring lines ( ) entering the average; for this weight, a Gaussian fall-off as a function of was chosen, with a FWHM width between 0 and 3.6 pixels (0 and ).
Our determinations of the heliocentric recession velocities and central velocity dispersions are collected in Table 3 (also available in electronic form). The radial-velocity and velocity-dispersion profiles are displayed in Fig. 3 and Fig. 6, and proposed in electronic form in Table 4. Individual results are discussed in Sect. 3. MdOH presented the redshift survey of the entire Hickson's sample; our measurements of the systemic velocities have been compared with their measurements and, for the seven galaxies in common, the average difference is km s-1, which is unsignificant.
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