Scientific/Technical Abstract:

FIFI-LS will have two separate medium resolution (R ~ 1700) liquid helium cooled grating spectrometers with common fore-optics feeding two large Ge:Ga detector arrays (16 x 25 pixels each). With the two Littrow spectrometers we can simultaneously observe an object in two spectral lines in the wavelength ranges 42 - 110 um, and 110 - 210 um, respectively, in 1st and 2nd order.

Multiplexing takes place both spectrally and spatially. An image slicer redistributes 5 x 5 pixel spatial fields-of-view (~ diffraction-limited in each wave band) along the 1 x 25 pixel entrance slits of the spectrometers. Anamorphic collimator mirrors help keep the spectrometer compact in the cross-dispersion direction.  The spectrally dispersed images of the slits are anamorphicly projected onto the detector arrays, to independently match spectral and spatial resolution to detector size, thus enabling instantaneously coverage over a velocity range of ~ 1500 to 3000 km/s around selected FIR spectral lines, for each of the 25 spatial pixels.

For calibration and flatfielding, black body calibrators internal to the instrument are used.  These have signal levels comparable to the thermal background of the telescope. An image rotator compensates for field rotation during long exposures.

FIFI LS Performance Summary – Instrument sensitivity and resolution summary is provided to permit estimating feasibility of scientific investigations.

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All sensitivity and resolution data are preliminary, and based on anticipated performance of the observatory and the instrument.  Actual performance of the SOFIA telescope and instrument combination will be established after flight operations begin.  Telescope performance is expected to be upgraded during the first two years, and instrument performance may be upgraded, or additional modes or capabilities may be added.

Performance estimates given here are based on data supplied by the instrument team. Further details and updates may be obtained from the instrument team via the contact information given above.

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