Final characterization and absolute flux calibration of FIFI-LS on SOFIA

We present the final characterization and absolute flux calibration of the FIFI-LS on SOFIA. The instrument was commissioned in 2014 and observed until September of 2022 when the SOFIA observatory was decommissioned by NASA. All the calibration data taken in the laboratory and in flight have been reanalyzed in order to reprocess the data acquired by the observatory in an optimal way as a closing activity of the observatory. We describe all the improvements achieved during this closing phase: (i) values of the precipitated water vapor have been estimated for every SOFIA flight and added to the raw data in the archive; (ii) More accurate values of the spectral resolution have been obtained by analyzing new laboratory data; (iii) The spatial point-spread function has been evaluated at key wavelengths using dedicated observations of the bright sky point sources; (iv) The flats have been updated by using a more robust approach; (v) The flux calibration has been improved by analyzing all the sky calibrators observed during the course of the mission.

A final version of the pipeline containing all the improved calibration data will be released in August 2023. The data from cycles 5 to 9 are being reprocessed using the new calibration and will be all archived on IRSA by the end of September 2023.