The data reduction pipeline for the VLT 2nd generation instrument X-Shooter
uses a physical model to determine the optical distortion and derive the
wavelength calibration. The parameters of this model describe the positions,
orientations, and other physical properties of the optical components in the
spectrograph. They are updated by an optimisation process that ensures the best
possible fit to arc lamp line positions. ESO Quality Control monitors these
parameters along with all of the usual diagnostics. This enables us to look for
correlations between inferred physical changes in the instrument and, for
example, instrument temperature sensor readings.Comment: 9 pages, 8 figures, style files included, Proc. of Observatory
Operations: Strategies, Processes, and Systems III, eds. D.R. Silva, A.B.
Peck, B.T. Soifer, SPIE 7737, 1