Model-based wavelength calibration for CRIRES

摘要

CRIRES, a first generation VLT instrument, is a cryogenic high-resolution (R~100,000) IR spectrograph operating in the range 1-5 μm. Here we present a model based wavelength calibration for CRIRES. The procedure uses a streamlined model of the CRIRES optical path that enables calculation of the location of the illumination in the detector focal plane at sub-pixel accuracy for a given wavelength and instrumental configuration. The instrumental configuration is described in terms of the tips and tilts of optical surfaces, their optical properties and environmental conditions. These parameters are derived through the application of a minimisation algorithm that is capable of using multiple realisations of the model to find the configuration which results in the optimal match between simulated wavelength data and dedicated calibration exposures. Once the configuration is accurately determined the model can be used to provide the dispersion solution for science exposures or to produce two dimensional simulated data for a given spectral source. In addition we describe comparisons to early laboratory data and the optimisation strategy adopted.