## Checking wavelength calibration

\label{sec:checkwave}

Both automatic and interactive reductions include a check of the wavelength calibration using the sky lines or telluric absorptions. This is computed by cross-correlating the sky lines either with a frame of sky lines observed in the past, or the telluric absorptions with a telluric model. These frames are stored in the directory “standard”. If the check on the wavelength calibration is performed on 1D frames, the third dimension of the file (produced by the iraf task $$apall$$) is used. If the check is performed on 2D wavelength calibrated frames, a median along the spatial axis is used. During the interactive reduction some plots are shown to the user for feedback. Examples of these plots are shown in Figs. \ref{fig:check} and \ref{fig:check2}.

## Fringing correction

\label{sec:fringing}

At the moment fringing correction is only applied to the red part of the spectrum. A keyword is added to the science frame if the fringing correction is applied. Science frames with name starting with ’n’ have been corrected for fringing. While reducing the data in interactive mode, if the correction for fringing is poor, users may try to use the option --fringing 2 and check if this improves the fringing correction. The keywords identifying the flat field used to correct for fringing are reported below.

FLATRED = 'flat_20130401_R642_56463.fits'
FLATBLUE = 'flat_20130401_R642_56463.fits'