1 Introduction

Several large objective-prism surveys have been done during the last two decades. They include pioneering work by Markarian 1967; Markarian et al. 1989 and later works (e.g. by Coziol et al. 1994), in which galaxies were primarily selected by strong UV-continuum. Other surveys, such as Tololo (Smith et al. 1976), University of Michigan (UM) survey (MacAlpine et al. 1977, 1981) and surveys by Wasilewski (1983); Moody et al. (1987); Zamorano et al. (1994, 1996) exploited the presence of emission lines in objective-prism spectra.

Two new large objective-prism surveys for ELGs applying new automatized algorithms of search: Hamburg/SAO survey (HSS, Lipovetsky et al. 1996; Ugryumov et al. 1998) and Kitt Peak International Spectral Survey (KISS, Salzer et al. 1994; Kniazev et al. 1996) using CCD as a sensitive detector are now near completion.

Two other large objective-prism surveys used both criteria (unusually strong UV continuum and strong emission lines) to select galaxies with signs of any kind of activity. The first is the Second Byurakan Survey (SBS), in which about 1500 galaxies were selected in the area of 1000 square degrees (Markarian et al. 1983; Stepanian et al. 1993) with a magnitude limit of about $m_{\rm pg} = 18\hbox{$.\!\!^{\rm m}$}0$.The Case Low-Dispersion Northern Sky Survey is another large survey which combines both selection criteria (Pesch & Sanduleak 1983; Sanduleak & Pesch 1984; Stephenson et al. 1992; Pesch et al. 1995). The Case survey includes also the lists of HII-regions in other galaxies, blue and carbon stars.

Follow-up spectroscopy of the objects selected in Schmidt telescope surveys is very fruitful to build up large samples of extragalactic objects with different kinds of activity -- from dwarfs and nuclei of large spirals with enhanced SFR to AGNs of various types from LINERs to QSOs.

In particular, much progress in studies of ELGs has been achieved after extensive studies of Markarian galaxies (Huchra & Sargent 1973; Huchra 1977; Mazzarella & Balzano 1986; Markarian et al. 1988) and the earlier cited therein, and studies of complete samples of ELGs selected from the UM and Wasilewski's surveys (Salzer et al. 1989a,b; Bothun et al. 1989). The follow-up spectroscopy of ELGs from the SBS resulted in many new active star-forming galaxies (Izotov et al. 1993; Stepanian et al. 1993).

The Case survey contains currently 1579 blue and/or emission-line galaxies (see Pesch et al. 1995, for the most recent list). It provides us with deep enough (the limit of about $m_{\rm CG} = 18\hbox{$.\!\!^{\rm m}$}0$) lists of ELG candidates in the large sky area. Spectroscopic observations for several subsamples of Case galaxies have been published by Tifft et al. (1986); Augarde et al. (1987); Weistrop & Downes (1988, 1991) and Weistrop (1989). Large work has been recently done by Salzer et al. (1995), presenting spectroscopy and CCD imaging of 176 Case galaxies from lists I and II.

Our current primary interest lies in studies of low-mass galaxies with star formation burst -- blue compact galaxies (BCGs). We assembled large statistical BCG sample on the basis of the follow-up spectroscopy of ELGs from the SBS, and studied the main properties of this sample (Izotov et al. 1993, 1994; Thuan et al. 1994, 1998; Pustilnik et al. 1995; Lipovetsky et al. 1989). To go further into the understanding of star formation (SF) in low-mass galaxies, new large well-selected samples are necessary.

The main goal of this paper is to build up a new large sample of BCGs in a large well-defined sky region. Thus we carried out the follow-up spectroscopy for those Case candidates, which left outside the scope of the previous slit-spectroscopy studies, in order to combine all available data and produce the BCG sample in the zone of Case survey.

One of the characteristics for a current intensive SF burst in a galaxy is the presence of strong [OIII]$\lambda\lambda$4959, 5007 emission lines in its spectrum. Therefore, to decrease the number of objects to observe and the time necessary to complete the project, we limited ourselves to only the Case galaxies having at least some indication on [OIII] $\lambda\lambda$4959, 5007 emission lines according to the Case survey classification. We emphasize that our working sample is in no way complete. It combines all Case ELG candidates which were not observed in earlier studies cited above, and thus by construction is highly heterogeneous. Therefore comparing directly their properties with those of other known and well selected ELG samples (like UM sample by Salzer et al. 1989) seems to be unreasonable. Instead we are going to undertake such comparison in the forthcoming article, where we try to combine all the published spectroscopy results for ELG candidates in the sky region discussed. The selection of Case galaxies for this program is described in more detail in Sect. 2. In Sect. 3 we describe the observations and data reduction. Section 4 presents the results of observations, attached in 3 tables. In Sect. 5 we give some preliminary analysis of the observational results, and in Sect. 6 we briefly summarize the results and draw some conclusions. All distance dependent parameters are derived for the Hubble constant 75 kms^-1 Mpc^-1.