FIFI-LS (the Field Imaging Far Infrared Line Spectrometer for SOFIA) was successfully commissioned in 2014 during six flights on SOFIA. The observed wavelengths are set by rotating reflective gratings. In flight these gratings and their rotating mechanisms are exposed to vibrations. To quantify these vibrations, an acceleration sensor was placed on the exterior of the instrument. Simultaneously, the angle sensor of the grating was read out to analyze the movement of the grating. Based on this data, lab measurements were conducted to evaluate the effect of the vibrations on the image quality of FIFI-LS. The submitted paper will present the measured data and show the results of the analysis.
Observing on the Stratospheric Observatory for Infrared Astronomy (SOFIA) requires a strategy that takes the specific circumstances of an airborne platform into account. Observations of a source cannot be extended or shortened on the spot due to flight path constraints. Still, no exact prediction of the time on source is available since there are always wind and weather conditions, and sometimes technical issues. Observations have to be planned to maximize the observing efficiency while maintaining full flexibility for changes during the observation. The complex nature of observations with FIFI-LS - such as the interlocking cycles of the mechanical gratings, telescope nodding and dithering - is considered in the observing strategy as well. Since SOFIA Cycle 3 FIFI-LS is available to general investigators. Therefore general investigators must be able to define the necessary parameters simply, without being familiar with the instrument, still resulting in efficient and flexible observations. We describe the observing process with FIFI-LS including the integration time estimate, the mapping and dithering setup and aspects of the scripting for the actual observations performed in flight. We also give an overview of the observing scenarios, which have proven to be useful for FIFI-LS.