Abstract
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.
Highlights
The Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS)[1] is the sensitive medium resolution (R ∼ 1500) spectrometer for the Stratospheric Observatory for Infrared Astronomy (SOFIA).[2]
We have proposed the upgrade presented in this paper, including a Legacy Science Program to National Aeronautics and Space Administration (NASA), in response to the SOFIA Generation Instrumentation call 2018
The spaxel size on the sky corresponds to 12.2 × 12.5 square arc sec, in the blue channel to 6.14 × 6.25 square arc sec. Both channels are equipped with a reflective integral field unit (IFU), which reorganizes the square 5 × 5 spaxel field of view (FOV) into a ð25 þ 4Þ × 1 spaxel slit, which is coupled into a quasi-Littrow mounted spectrometer
Summary
The Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS)[1] is the sensitive medium resolution (R ∼ 1500) spectrometer for the Stratospheric Observatory for Infrared Astronomy (SOFIA).[2] FIFI-LS operates two spectral channels from 51 to 125 μm and 115 to 203 μm simultaneously. It allows fast mapping of the fine structure cooling lines of the interstellar medium (ISM) and.
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