The reduction of FORS2 data at QC1 Garching is done in a semi-automatic manner where raw data are inserted into an automatic reduction machine. This machine is the FORS2 reduction pipeline.
The main functionalities of the FORS2 pipeline are:

• to produce master calibration data
• to compute QC1 parameters

Since April 1, 2008, the new imaging pipeline has been in operation. Information on the imaging pipeline used before can be found here.

OPERATIONS

There are two instances of the FORS2 reduction pipeline:

• the automatic mode, running on Paranal,
• the optimized mode, running at HQ Garching and operated by Quality Control.

The optimized mode is the mode, which only becomes possible when all data of a night have been collected. Then the calibration data are sorted and assessed independently of their timestamp. The best possible master calibration data are created. Their quality is checked. They are finally applied to the science data of a night. This is the way all calibration data are reduced by QC Garching, as are all science data from Service Mode programmes.

FUNCTIONALITIES

The FORS2 pipeline is run by QC Garching for all the supported modes and produces:

• master calibration data
  These are produced for both Visitor Mode and Service Mode nights. The raw calibration data are stored in the ESO Archive and are publicly accessible.
• QC1 parameters
  These are computed for all the master calibration data. These are used to assess the quality of the master calibration data and to trend the instrument evolution. The QC1 parameters are availble through the QC1 web pages.
• reduced science data.
  These are produced for Service Mode nights. These data are produced using the best available QC-assessed master calibration data.

FILE FORMAT

During the FORS2 detector upgrade on March 22, 2002, the old CCD has been replaced by a mosaic of two red/IR-optimized CCDs. The upper CCD is referenced as Chip1 (also called master), while the lower CCD is referenced as Chip2 (also called slave). Each FORS2 exposure is split into two files, one for each CCD.
The CCD mosaic is mounted off-axis so that the target falls by default on Chip1 and gap between the two CCDs falls between two MOS slits.

The raw FORS2 files in the standard CCD format (2x2 binning, no windowing) have 2048x1034 pixels. The field of view is limited by the MOS unit, therefore the field of Chip1 is larger than that of Chip2. Two pre/overscan regions are present in the CCD. For the standard CCD format (2x2 binning), these regions are 5 pixels wide (i.e. rows 1...5 for the prescan and 1030...1034 for the overscan). For a graphical description of the detector sections, have a look here (pre-view) or here (ps file). Note that for presentation reason, the pre-scan regions have been artificially enlarged.

SUPPORTED MODES AND SETTINGS

The FORS2 pipeline installed in Garching and on Paranal presently supports only the following instrument modes and settings. Non-standard settings are not supported by the pipeline.

Supported Modes	Supported Settings
Imaging  (IMG)	Binning: 2x2, 1x1 Gain: low, high Collimator: SR/HR Windowing: no Filters: all
Long Slit Spectroscopy (LSS)	Binning: 2x2, 1x1 Gain: high Collimator: SR/HR Windowing: no Grisms: all
Multi Object Spectroscopy (MOS/MXU)	Binning: 2x2, 1x1 Gain: high Collimator: SR/HR Windowing: no Grisms: all

The HIT modes are presently not supported by the pipeline. In this case, only raw calibration data are delivered for Service Mode programmes.