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Astron. Astrophys. 318, 405-415 (1997)

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2. Observations

Since the observations are described in detail in Paper I, only a short summary will be given here. Four regions were chosen for our program. In two of them the line of sight crosses several known voids behind each other. From the two void regions VN2 and VN4 selected for their emptiness and from the cluster A2151 we obtained deep direct images on the prime focus of the Calar Alto 3.5m telescope. Using photographic plates together with the K3 field corrector a field of roughly 1 [FORMULA] was mapped for each exposure. In addition, using a Tektronix 10242 pix CCD-chip for scanning, a mosaic of frames with roughly another 1 [FORMULA] field in total was covered towards the void region VN8.

On these images we searched for galaxies with diameters larger than [FORMULA] 5 and identified 637 objects (Sample 2 of Paper I). Of these 178 objects with diameters above [FORMULA] 5 were selected (Subsample 2 of Paper I). Finally, 77 objects were chosen for follow-up spectroscopy due to their non-giant morphology (e.g. late types or LSB's) and spectroscopic information as well as redshifts could be derived for all of them.

Additional POSS plates towards VN2, VN8 and A2151 were searched through for objects with diameters larger than [FORMULA]. From the 922 objects found within about 150 [FORMULA] (Sample 1 of Paper I) we selected 362 candidates according to the same morphological criteria (Subsample 1 of Paper I). Of these 77 were classified as targets of first priority and 285 of second priority (Table 2 of Paper I). Because of limited observing time redshifts have been measured only for 61 objects of both priorities. Due to the low field density of the selected objects the spectroscopy for both samples had to be done by single-slit observations.

Besides the redshift, Paper I contains apparent B and R magnitudes, colour, mean surface brightness, apparent major and minor diameters and the morphological type for nearly all of our galaxies. The same data for the additional 15 galaxies, found on the POSS plates towards VN2 and VN8, are given in the appendix here. They have been obtained in two later observing runs.

A further 40 galaxies of Table 10, Paper I and the appendix are included in the following discussion: 18 "Back-up objects" plus 22 indicated with a preceding N (15 in Sample 1, 5 in Sample 2, 2 Back-up). Of the former, a few are brighter than [FORMULA].

Newly measured redshifts are therefore available from 193 galaxies in total: 91 "POSS"- , 82 "K3/CCD"- and 20 "Back-up"-objects. For 185 of these, B and R magnitudes are known.

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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