VIMOS is the Visible Multi-Object Spectrograph mounted at the Nasmyth
focus of the 8.2m Melipal (UT3) telescope of the ESO Very Large Telescope. VIMOS operates with four channels in three observing modes: imaging, multi-object spectroscopy (MOS), and integral field spectroscopy. VIMOS data are pipeline-processed and quality-checked by the Data Flow Operation group in Garching. The quality check is performed in two steps. The first one is a visual check of each pipeline product that allows the identification of any potential major data problem, such as, for example, a failure in the MOS mask insertion or an over/under exposure. The second step is performed in terms of Quality Control (QC) parameters, which are derived from both raw and processed data to monitor the instrument performance. The evolution in time of the QC parameters is recorded in a publically available database (http://www.eso.org/qc/). The VIMOS QC parameters include, for each of the four VIMOS channels, the bias level, read-out-noise, dark current, gain factor, flat-field and arc-lamps efficiencies, resolution and rms of dispersion, sky flat-field structure, image quality and photometric zeropoints. We describe here some examples of quality checks of VIMOS data.
Currently four instruments are operational at the four 8.2m telescopes of the European Southern Observatory Very Large Telescope: FORS1, FORS2, UVES, and ISAAC. Their data products are processed by the Data Flow Operations Group (also known as QC Garching) using dedicated pipelines. Calibration data are processed in order to provide instrument health checks, monitor instrument performance, and detect problems in time. The Quality Control (QC) system has been developed during the past three years. It has the following general components: procedures (pipeline and post-pipeline) to measure QC parameters; a database for storage; a calibration archive hosting master calibration data; web pages and interfaces. This system is part of a larger control system which also has a branch on Paranal where quick-look data are immediately checked for instrument health. The VLT QC system has a critical impact on instrument performance. Some examples are given where careful quality checks have discovered instrument failures or non-optimal performance. Results and documentation of the VLT QC system are accessible under http://www.eso.org/qc/.
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