We present the initial design, performance improvements, and science opportunities for an upgrade to the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS). FIFI-LS efficiently measures fine structure cooling lines, delivering critical constraints of the interstellar medium and star-forming environments. The Stratospheric Observatory for Infrared Astronomy (SOFIA) provides the only far-infrared (FIR) observational capability in the world, making FIFI-LS a workhorse for FIR lines, combining optimal spectral resolution and a wide velocity range. Its continuous coverage of 51 to 203 μm makes FIFI-LS a versatile tool to investigate a multitude of diagnostic lines within our galaxy and in extragalactic environments. The sensitivity and field of view (FOV) of FIFI-LS are limited by its 90s-era photoconductor arrays. These limits can be overcome by upgrading the instrument using the latest developments in kinetic inductance detectors (KIDs). KIDs provide sensitivity gains in excess of 1.4 and allow larger arrays, enabling an increase in pixel count by an order of magnitude. This increase allows a wider FOV and instantaneous velocity coverage. The upgrade provides gains in point source observation speed by a factor >2 and in mapping speed by a factor >3.5, enabled by the improved sensitivity and pixel count. This upgrade has been proposed to NASA in response to the 2018 SOFIA Next Generation Instrumentation call.
We present the initial design, performance improvements and science opportunities for an upgrade to the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS). FIFI-LS efficiently measures fine structure cooling lines, delivering critical constraints of the interstellar medium and starforming environments. SOFIA provides the only FIR observational capability in the world, making FIFI-LS a workhorse for FIR lines, combining optimal spectral resolution and a wide velocity range. Its continuous coverage from 51-203 microns makes FIFI-LS a versatile tool to investigate a multitude of diagnostic lines within our galaxy and in extragalactic environments. The sensitivity and field-of-view (FOV) of FIFI-LS are limited by its 90s-era photoconductor arrays. These limits can be overcome by upgrading the instrument using the latest developments in Kinetic Inductance Detectors (KIDs). KIDs provide sensitivity gains in excess of 1.4 and allow larger arrays, enabling an increase in pixel count by an order of magnitude. This increase allows a wider FOV and instantaneous velocity coverage. The upgrade provides gains in point source observation speed by a factor <2 and in mapping speed by a factor <3.5, enabled by the improved sensitivity and pixel count. This upgrade has been proposed to NASA in response to the 2018 SOFIA Next Generation Instrumentation call.
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.
KEYWORDS: Observatories, Spectroscopy, Data archive systems, Advanced distributed simulations, X-rays, Data centers, Analytical research, Current controlled current source, Data analysis, Databases
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.
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