The aim of project DR07 is to provide an advanced sky correction tool that removes sky emission in science spectra by means of sky spectra taken at a different time. The algorithm adapts a reference sky spectrum to a science spectrum by correcting differences due to airglow variability and issues related with the instrument or the data reduction. The approach is based on a similar method for SINFONI near-IR spectroscopic data described in Davies (2007, MNRAS 375, 1099). For spectroscopic instrument setups and observing programmes that do not provide pure sky spectra in parallel to the desired object spectra (e.g. two-dimensional long-slit spectra where the object does not cover the whole slit), it is necessary to use sky spectra taken at a different time as the science spectra for the sky correction. However, the strong variability of airglow emission on time scales on the order of a few minutes can cause unavoidable sky correction residua. Moreover, different telescope positions and ambient conditions may cause instrument flexures, which result in shifting of the sky with regard to the science spectrum. Hence, the reference sky spectrum has to be adapted in both, the flux and the wavelength regime, to allow a reasonable sky background correction. The project provides a stand-alone tool and a Reflex workflow for incorporation in suitable ESO data reduction pipelines. This model is extended by identifications of lines with similar upper and lower electronic, vibrational, and/or rotational states that are expected to vary in a very similar way. If the spectral resolution is given, the DR05 airglow emission model with the improved line list (ranging from 0.3 to 2.5 μm) allows deriving the contributions of different line groups to the pixels of a sky spectrum. Other than in the original method, which uses fixed wavelength intervals, we use the physics of the excitational levels for the selection of the variability groups. The whole user documentation is given in the ESO document archive as Nr.: VLT-MAN-ESO-19550-5504
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