2. Data acquisition

Long-slit spectra were taken at the CTIO 1.5 m telescope in February 1996. We used a Loral CCD (1 pixel ), grating #13 with centered on 5000 Å in first order. In this configuration the wavelength range covers from to 8500 Å with a reciprocal dispersion of 5.6 Å/pix. The CCD gain was fixed on and a corresponding readout noise of . During the galaxy observations the slit was fixed on 130 microns resulting in a final spectral resolution of 14.4 Å. Wavelength calibration was done with He-Ar comparison lamp. However, since the CCD sensitivity drops quite abruptly in the blue we needed to make two separated calibration exposures. A deep calibration was adopted for the extreme blue with . For the red a normal exposure of of was sufficient to obtain good calibration lines.

Typical exposure time for our objects were three observations of in order to be able to remove cosmic rays more easily. We have also observed a sample of late type stars for radial velocity calibration and CTIO spectrophotometric standard stars (Baldwin & Stone 1984). In Table 1 (click here) we present a list of observed galaxies with the same identification code adopted by Soares et al. (1995).

 

g238b 158-0060 15.3 0 11769 11 12 0.75 11950 5 2 0.09 - -

g240a 203-0070 14.3 -3 5376 10 15 0.85 0.08 334 1060

g240b 203-0040 14.5 4 4316 14 10 0.70 4345 60 3 0.46 334 1060

g255b 486-0180 15.6 1 12563 15 9 0.70 0.06 423 123

g266b 158-0200 15.4 3 10304 12 8 0.60 0.19 376 459

g266bc 158-0201 15.5 1 9845 13 13 0.74 0.14 376 459

g267a 486-0380 14.6 -3 4156 8 15 0.85 0.08 - -

g276a 305-0220 14.6 3 4627 9 6 0.52 4640 38 6 0.87 - -

g276b 305-0310 14.6 4 15114 9 8 0.71 0.08 - -

g277b 305-0230 15.4 1 11717 14 12 0.72 0.07 448 156

g277bc 305-0231 16.4 6 11561 15 12 0.76 0.08 448 156

g278a 253-0040 13.4 -5 4339 7 12 0.82 4224 0.05 209 41

g278b 253-0010 14.7 7 4380 38 6 0.33 0.51 209 41

g280a 306-0030 14.4 4 4687 0 11 0.66 4613 - 2 0.38 - -

g280b 306-0011 15.4 1 11138 10 13 0.66 11022 86 2 0.07 494 83

g280bc 306-0010 15.5 1 11055 10 10 0.63 11084 39 3 0.32 494 83

g281a 204-0200 14.6 5 10347 15 10 0.65 10341 0.16 - -

g281b 204-0190 14.8 6 4503 12 6 0.39 4706 66 3 4523 0.50 - -

g284a 568-0090 14.3 6 3007 13 11 0.63 2724 - 1 0.27 - -

g284b 568-0080 14.7 -5 5577 11 11 0.82 0.02 - -

g304a 305-0150 14.0 -4 7467 11 8 0.79 7541 -0.01 263 289

g304b 505-0170 15.8 0 7756 11 10 0.78 0.01 263 289

g307a 506-0010 13.3 -4 3297 9 14 0.86 3275 0.06 95 33

g318b 443-0220 16.0 8 3531 40 5 0.40 3433 - 2 0.52 93 277

g323a 443-0500 14.5 -2 5664 11 10 0.83 0.03 44 230

g323b 443-0510 15.6 3 5434 16 9 0.61 5185 80 0.19 44 230

g331a 444-0101 14.3 1 9304 10 10 0.78 0.07 23 53

g331b 444-0100 15.4 6 8986 38 8 0.42 9039 120 2 0.22 23 53

g340a 576-0760 13.9 -4 1695 9 15 0.86 0.04 - -

g340b 576-0730 15.1 6 5561 57 8 0.51 5533 39 4 0.50 - -

g344a 444-0760 14.4 -1 4273 9 15 0.85 0.08 36 426

g350a 509-1010 14.3 -1 6805 9 9 0.79 6827 0.03 160 238

g351a 445-0510 14.6 -1 5000 10 14 0.78 5050 72 2 4995 0.13 169 321

g351b 445-0480 15.6 7 4679 26 9 0.48 4686 117 3 0.40 169 321

g357b 510-0550 15.7 3 6167 12 10 0.66 6111 43 6 0.18 - -

g361b 578-0260 15.7 6 10891 16 9 0.74 0.00 - -

g362a 578-0290 14.3 -5 8720 11 12 0.82 0.05 287 19

g362ac 8950 12 9 0.27 0.02 287 19

g362b 578-0320 15.1 2 8701 11 10 0.80 0.03 287 19

g363a 511-0180 14.5 3 6395 10 13 0.71 6337 31 2 0.24 43 14

g363b 511-0200 15.6 3 6381 14 12 0.63 6461 - 1 0.14 43 14

g373a 580-0430 13.8 -3 5990 11 10 0.79 6054 0.23 - -

g373b 580-0410 14.3 3 2954 23 6 0.48 3004 58 3 0.36 - -

g375a 581-0240 13.7 7 2422 51 5 0.30 2279 0.27 - -

g375b 581-0220 13.7 1 4264 9 13 0.83 4266 0.05 - -

n1741 13.8 P 4136 16 10 2.40 - -

n3819 6274 11 13 0.84 0.03 - -

n3557 337-0160 11.5 -5 2917 10 13 0.85 3151 0.03 - -

n3923 440-0170 10.6 -3 1788 11 11 0.84 1788 -- - -

n4273 12.0 5 2415 17 7 0.60 2492 29 3 2386 0.62 - -

u4703a1 3573 46 9 0.86 - -

u4703a2 3536 23 4 0.36 3580 34 6 - -

 

Standard data reduction techniques were followed using the IRAF package. The extraction was done with apall task in each one of the spectra and later on combined to a single spectra removing the eventual presence of cosmic rays. We used the optimal extraction algorithm (Horne 1986) with weights computed from the estimated noise. The tracing and sky subtraction of each object was interactively determined for each image. The extracted spectra were wavelength calibrated and rebinned to a linear scale of 5 Å in the range . A correction for sensitivity was also applied adopting the average determination on the 5 observed nights using our spectrophotometric observations and the mean extinction coefficient for CTIO.

The radial velocities were determined from the cross correlation package of IRAF, using standard velocity stars as templates. In objects with strong emission lines we have eliminated these regions before applying the correlation technique on the absorption lines. Besides the standard stars, we have also observed a sample of 12 galaxies with known radial velocities. A comparison of our measurements with the literature resulted that the mean RMS error on our determination is of the order of . Moreover, we have also detected a systematic drift of which was removed from our velocities. From those objects with emission lines we have also determined the emission velocities and the two determinations are consistent to within an error of . Our results are shown in Table 1 (click here). In the first two columns we present the object identification as it is described in Soares et al. (1995) and the ESO identification code. In Cols. 3 and 4 we present the total blue magnitudes and the morphological type extracted from the ESO-LV catalog (Lauberts & Valentijn 1989). The absorption line velocities and estimated error () are presented in Cols. 5 and 6. In Cols. 7 and 8 we present the R quality parameter of Tonry & Davis (1979) and the peak value of the correlation spectra. For a few objects we were able to determine the emission line velocities (Cols. 9 and 10) based on the number of observed lines (Col. 11). In Col. 12 we have the radial velocities of the objects collected from the ZCAT redshift catalog (Davis & Huchra 1982). In Col. 13 we show the mean residual parameter in the blue, that will be defined in Sect. 3 bellow. In the last two columns we present the projected separation in kpc and the velocity difference in using h=1.

  
Figure 1: The projected pair separation distribution showing that our sample (solid line) have a larger contribution of loose pairs then the Karachentsev sample (dashed line)