Scientific/Technical Abstract:

To take advantage SOFIA's unique potential for high resolution spectroscopy in the mid-infrared, the Echelon-Cross-Echelle Spectrograph (EXES) to operate in three spectroscopic modes (R~10⁵, 10⁴, and 3000) from 5 -28 microns.

EXES will use a 256² Si:As BIB detector. High dispersion is provided by an echelon, a coarsely-ruled, steeply-blazed aluminum reflection grating. Using the echelon requires an echelle grating to cross-disperse the spectrum, resulting in continuous wavelength coverage of ~5 cm^-1 and a slit length of ~10" at R=10⁵. Optionally, the echelon can be bypassed so that the echelle or a low order grating acts as the sole dispersive element. This results in a single order spectrum with slit length of roughly 90" and R=10⁴ or 3000, respectively. The low resolution grating also serves as a slit positioning camera when it is rotated face on.

One of the greatest advantages of SOFIA will be its ability to study molecules which are blocked by the Earth's atmosphere. In particular, high spectral resolution enables the study of molecular hydrogen, water vapor, and methane from sources such as molecular clouds, protoplanetary disks, interstellar shocks, circumstellar shells, and planetary atmospheres.

EXES 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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