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Дата изменения: Fri Jun 8 14:28:15 2001
Дата индексирования: Sat Sep 11 20:24:45 2010
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Data reduction

Reduction of the CAHA and KPNO spectral data was performed at the SAO using the standard reduction systems MIDAS and IRAF.

The MIDAS command FILTER/COSMIC was found to be a quite successful way to remove automatically all cosmic ray hits from the images. After that we applied the IRAF package CCDRED for bad pixel removal, trimming, bias-dark subtraction, slit profile and flat-field corrections.

To do accurate wavelength calibration, correction for distortion and tilt for each frame, sky substraction and correction for atmospheric extinction, the IRAF package LONGSLIT was used with invoking the IDENTIFY, REIDENTIFY, FITCOORD, TRANSFORM, BACKGROUND and EXTINCTION tasks.

To obtain an instrumental response function from observed spectrophotometric flux standards, the APSUM procedure from the APEXTRACT package was used first to extract apertures of standard stars. Then the sensivity curve determined by the STANDARD and SENSFUNC procedures was applied by the CALIBRATE task to perform flux calibration for all object images. Finally the APSUM task was used to extract one-dimensional spectra from the flux calibrated images. In case that more than one exposure was obtained with the same setup for an object, the extracted spectra were co-added and a mean vector was calculated. In case of several observations with different setups (telescopes or grisms) for the same object, the data were reduced and measured independently and the more reliable values were taken.

To speed-up and facilitate the line measurements we employed dedicated command files created at the SAO using the FIT context and MIDAS command language. The procedures for the measurement of line parameters and redshifts applied were described in detail in Papers III and IV.