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Introduction

Several large objective-prism surveys have been done during 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. [1997]) and Kitt Peak International Spectral Survey (KISS, Salzer et al. [1994]; Kniazev et al. [1996]) and using CCD as a sensitive detector are now near completion.

Two other large objective-prism surveys used the 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 & Stepanian [1983]; Stepanian et al. [1993]) with the magnitude limit of about m_b = 18 mag. The Case Low-Dispersion Northern Sky Survey is another large survey which combines the 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 kind 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 actively 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_b =18 mag) 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 178 Case galaxies from lists I and II.

Our current primary interest lies in studies of dwarf 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 of the main properties of this sample (Izotov et al. [1993], [1994]; Thuan et al. [1994], [1997]; Pustilnik et al. [1995]; Lipovetsky et al. [1996]). To go further in understanding 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 behind 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 by 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 sense complete. It combines all Case ELG candidates which were not observed in earlier studies cited above, and thus by construction is highly heterogeneous. Therefore to compare 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 section 2. In section 3 we describe the observations and data reduction. Section 4 presents the results of observations, attached in 3 tables. In section 5 we give some preliminary analysis of the observational results, and in section 6 we briefly summarize the results and draw some conclusions. All distance dependent parameters are derived for the Hubble constant 75 km s^-1Mpc^-1.