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IPCS observations and data reduction

Spectra obtained in the IPCS mode with the grating B1 (600 grooves/mm) cover the range of 3600 - 5500 Å with a dispersion of 1.9 Å/pixel. The spectra were obtained through round apertures with a diameter of 1.5'' to 3'' depending on the seeing, centered on the brightest part of the galaxy, usually near its center. Sky spectrum was accumulated simultaneously in the aperture of the same size displaced by 20'' along the current azimuth direction. A typical exposure time was 3-5 min (snap-shot mode) in order to detect the strongest emission lines [OIII] $\lambda\lambda$4959,5007, H$\beta$and [OII] $\lambda$3727 from the spectra with low S/N ratio, usually not exceeding 5-10 in continuum.

During photometric nights we have observed also spectrophotometric standards from the KPNO list (Massey et al. [1988]). These observations then were used to correct the spectra of the program galaxies for the system spectral response. He-Ne-Ar source was used as the reference spectrum. Flat-field was accumulated every night before and after the observations and all the spectra were corrected for the flat field after azimuth and modulation correction of the original 1024-channel arrays. The data reduction was done in MIDAS (93NOV version), with several programs from the contexts Spec and Long combined into the special package and adopted to perfom automatic mode reduction for IPCS 1-D spectra (Kniazev [1994]).