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Дата изменения: Wed Apr 14 14:21:19 1999
Дата индексирования: Sat Sep 11 20:28:59 2010
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Data reduction

The data reduction was done at SAO with the MIDAS software package. The context LONG was adapted to the SAO data formats to perform an automatic reduction. The reduction of the originally two-dimensional CCD data included standard steps such as: bias and dark subtraction, flat-fielding, cosmic-ray removal. After wavelength mapping the subsequent night sky background subtraction was performed. 1-D spectra were extracted by adding 6-10 (depending on seeing and galaxy size) consecutive CCD rows centered on the object intensity peak along the slit. Then the corrections for atmospheric extinction and flux calibration were applied. For the flux calibration we used the mean response curve obtained from the observations of standard stars, mainly Feige 34 and HZ 44.

In the final spectra showing emission lines, redshifts and line fluxes are measured applying Gaussian fitting. To determine redshifts for individual galaxies averages are taken over prominent individual emission lines (mostly H$\beta$, H$\alpha$, [O III]$\lambda$4959,5007 Å). The line [O II]$\lambda$3727 Å is not used for redshift determination since for most of the objects its observed wavelength is determined with significantly larger uncertainties due to the extrapolation of the linear scale below the first line of He I$\lambda$3889 Å in the reference spectrum.

The emission line fluxes are computed by summing up the pixel intensities inside the line region by using standard MIDAS program tools. For all spectra, the individual emission line fluxes of the H$\alpha$, [N II] $\lambda\lambda$6548,6583 Å and [S II] $\lambda\lambda$6716,6731 Å line blends are obtained by summing up of pixel intensities over the total blend and then modelling the individual line fluxes using Gaussian fitting.