pixels are widely used in solar and
stellar astronomy.
A few years ago, cameras with chips of
2048 pixels were
put into operation for example at NSO, Sacramento Peak (see Kuhn et al.
1997) and at the German Vacuum Tower Telescope (VTT)
operated by the Kiepenheuer-Institut für Sonnenphysik (KIS), Observatório del
Teide, Tenerife (Kentischer & Schleicher 1997).
New advanced computer technology, huge storage media capabilities and the
high speed of data handling has brought the ability to take long time
series of spectra with a high cadence of exposures.
Several general guide books and articles appeared to help with reduction and
restoration of the CCD spectra and images (e.g. Martines & Klotz
1998; Beletic & Amico 1998; Holst 1998;
Newberry 1999).
Nevertheless, any specific goal needs special arrangements for reductions
which are not given in the references mentioned above.
(See for example Harrison 1999, for flat-fielding of the solar
long-slit spectra.)
The aim of this paper is to introduce the reduction of solar CCD spectra taken with high spectral, spatial and time resolution, in long time series of several hours before and/or after the moment of the flat-field frames acquisitions. We will illustrate the whole process of reduction using solar high resolution 2D spectra taken with a large CCD detector.
The basic definitions are summarized in Sect. 2 and the observations are described in Sect. 3. We demonstrate the complete reduction process including an analysis of the spectrograph drift and the importance of different types of flat-fields in Sect. 4. Results are given in Sect. 5. The final discussion is presented in Sect. 6, where we compare and discuss the accuracy of three different types of reduction.
Copyright ESO 2002