Downes & Shara (1993, hereafter DS93) have compiled a very
useful catalogue and atlas of the Cataclysmic Variables discovered through
February 1992. A similar work for classical novae was presented by Duerbeck
(1987, hereafter D87). DS93 listed references to published quiescence
spectra for 271 objects and to outburst spectra for additional 123 systems
(in both cases a significant fraction belonging to the pre-digital
era), but for 359 objects (
half of the total) they have been unable
to locate published spectra.
In Papers I, II and III of this series (Zwitter & Munari 1994-1996) we have begun to present CCD spectra for CVs listed by DS93 as lacking published spectroscopy.
The results of Papers I, II and III confirm the conclusion of DS93 and D87 that the classification of an object as a CV using exclusively the information from photometric observations and/or automated spectral surveys may be misleading. The large fraction of mis-classifications we have encountered so far supports the need for a spectroscopic survey to prune the excellent DS93 catalogue from mis-entries.
In this paper we present flux-calibrated CCD spectra for additional 31 faint systems selected among those without published quiescence spectra according to the DS93 catalogue. The programme continues and observations of additional targets will be presented in future papers of this series.
Beside the confirmation of the CV status, our spectra are intended to expand the set of validated CVs with flux calibrated spectra. A physical analysis of spectral characteristics of the whole investigated sample is postponed to a final paper in this series.