Modeling the image distortion of echelle spectrographs with T&P changes

Even slight changes of temperature and pressure in high resolution ´Echelle spectrographs affect the spot image on the detector plane. At the same time astronomical applications require a stability of the measurement of up to 1/3000 of a pixel on the CCD (with a typical pixel size being 15μm). With this paper we present a study of the effects of thermal and pressure instabilities on ray tracing models of a typical ´Echelle spectrograph. We conclude the required minimum stabilty in these two parameters to reach the goal of precision spectroscopy.