Wavelength range: 5 - 40 µm. FORCAST has two arrays (Si:As for ~5 - 25 µm, and Si:Sb for ~25 - 40 µm) that can be used to simultaneously observe the same FOV.
Top right graph: An ATRAN model of the atmospheric absorption as a function of wavelength in the FORCAST band (assuming zenith angle 45 degree and 7 µm of precipitable H2O).
Bottom right graph: Filters include COTS line and continuum, and interference filters. Representative filter profiles are plotted.
In-flight atmospheric transmission at grism resolution R = 2000, with planned broadband filter passbands, and grism orders indicated by labeled horizontal bars.
Short wavelength filters (as of 12/01):
5.61 µm (R=70)
7.69 µm (R=15)
6.61 µm (R=34)
8.61 µm (R=42)
Cont. (R=34)
11.28 µm (R=56) 1
8.7 µm (R=15)
18.7 µm (R=15)
21.0 µm (R=15)
24.4 µm (R=30)
Long wavelength filters (as of 10/01):
32.0 µm (R=15)
cont. (R=800)
33.4 µm (R=30)
33.4 µm (R=800) 3
4.8 µm (R=30)
34.8 µm (R=800)
> 36 µm (R=10)
37.6 µm (R=15)
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Sensitivity is shown for a continuum point source, at the effective wavelengths of ten of the filters listed on page one. The Minimum Detectable Continuum Flux (MDCF) in mJy needed to get S/N = 4 in 900 seconds is plotted versus wavelength.
The red dots correspond to the expected SOFIA image quality at first light: 5.3 arc-sec (80% enclosed energy); the blue dots correspond to final SOFIA image quality: 1.6 arc-sec (80% enclosed energy).
MDCF scales roughly as (S/N) /Ã t where t = net integration time
Calibration and setup overhead is roughly 10%. If telescope nodding is used during observations, this may also increase total observing time needed by 5% to 10%.
Atmospheric transmission will affect sensitivity, depending on water vapor overburden.
Sensitivity is also affected by telescope emissivity. Values plotted above are for telescope emissivity = 15%. At telescope emissivity = 5%, sensitivity would be 20% to 60% better (fainter).
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FORCAST field of view is 3.2 arcminutes square (256 x 256 pixels). Imaging scale is 0.75 arcseconds per pixel. The camera optics are diffraction limited longward of l=15 mm.
FORCAST angular resolution (FWHM, arcÐseconds) versus wavelength for different observatory performance specs. The two image quality values are 80% enclosed energy diameters.
SOFIA and all first light focal-plane instruments are now in development. All sensitivity and resolution data are preliminary, and based on anticipated performance of the observatory and the instruments. 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 TEAMS. A POINT OF CONTACT FOR EACH INSTRUMENT IS PROVIDED.
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