We have studied the properties of wavelength calibration sources for the near-IR (NIR: 1000-2500 nm) arm of X-shooter.
In a novel approach we are combining laboratory measurements from a Fourier Transform Spectrometer (FTS)
and literature data with corresponding simulated data derived from a physical model of X-shooter. The sources studied
are pen ray lamps filled with the noble gases Ne, Ar, Kr, and Xe and Th-Ar hollow cathode lamps. As a product we
provide a quantitative order by order analysis of the expected properties of the calibration lamps during X-shooter
operations. The analysis accounts for blending of lines and makes realistic assumptions about the dynamic range
available in a typical wavelength calibration exposure. Based on our study we recommend the use of Ne, Kr, and Ar as
the best three lamp combination for X-shooter calibration. A detailed comparison between the predicted and actual
performance of the calibration system has been started as part of the X-shooter testing and validation phase and first
results are very promising. To our knowledge this is the first time that such a detailed and quantitative analysis of a
calibration system has been done prior to the operation of the instrument. The combination of laboratory measurements
and instrument modeling provides a powerful tool for future instrument development.
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