Any astronomical instrument located at the RC focus of a telescope is subject of mechanical flexures. These flexures at the end degrade the imaging quality of the instrument as well as introduces for example shifts in the spectral lines affecting the quality of the final spectra. In principle, the flexures could come from any motions of the wheels or mechanical components inside the instrument as well as from mechanical flexure in the structure of the instrument.
The procedure proposed is to take exposures of a star at different zenith distances with a given instrument setup. It will also help to take argon exposures in spectroscopy mode to find out any shifts of the spectral lines depending of the position of the telescope. The same experiment can be repeated rotating the instrument.
Therefore, for a given configuration: wide field, slit-100, K-band filter and the grism1, we plan to take frames for differents elevations in steps of 15 degrees. This will be repeated for the four directions (i.e. north, south, east and west) and after we will do the same for the hour angle. See more details in the results section.
Here you can find some preliminar results that suggest a clear distortion in the mechanical structure of OMEGA-Cass.
To avoid these distortions, the option to move the optic wheel by software is disable. It's possible to use all the optics, but you have to choose one and the staff will fixe it manually.