Wavelength range: 0.3 Ð 1.1 µm
Dual-channel high-speed direct imaging photometer. Modes include:
Single frames Shuttered time series Frame transfer time series up to 50 Hz Short
time series up to 10 KHz
Broadband imaging filters: Standard UBVRI passbands
Narrow-band filters at, e.g.: Methane filter at 0.89 µm
Dichroic Reflectors: HIPO will use a dichroic reflector to separate its channels. The transition wavelength for the first light dichroic has not been determined.
Additional Filters: Additional custom filters will be added for specific events
HIPO will include standard Johnson filters at first light that will be used primarily for facility performance testing. Occultation observations will normally be unfiltered for events involving faint stars or will use specialized filters such as the methane filter shown here for events with bright stars. The dichroic response shown here is only an example.
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HIPO first-light sensitivity is shown here for several representative cases. The upper figures correspond to occultations by Pluto or Triton while the lower two are for the case of a very faint occulting object. The left and right figures are for 0.5 sec and 50 ms integrations, respectively. Each figure shows S/N for no filter (dichroic only) and for the dichroic plus standard Johnson filters. The dichroic transition is assumed to occur from 0.57 and 0.67µm.
The deviation of S/N from a square root dependence is mostly due to shot noise on the occulting object in the top two figures, mostly to shot noise on the sky in the bottom left figure, and mostly to read noise in the bottom right figure. The improved final SOFIA pointing stability will increase sensitivity for sky-limited events and improve discrimination from nearby bright objects (e.g. Neptune for a Triton occultation).
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Format: 1024 x 1024 pixel array
Low resolution: 0.33Ó x 0.33Ó pixel
High resolution: 0.05Ó x 0.05Ó pixel
Pixels will normally be binned to best match the seeing blur size and to reduce the effect of read noise. High resolution mode includes no reimaging optics and will be used for shear layer imaging tests and for maximum throughput for certain occultations. Occultation photometry will be extracted from data frames using effective aperture sizes comparable to the 80% enclosed light diameter plotted here. The HIPO field is a 5.6Õ square inscribed in the 8Õ diameter SOFIA field.
The graph shows the expected instrument FWHM beam diameter as a function of wavelength. It is expected to be dominated by seeing and image motion effects. The red curve in this figure is the nominal image quality expected at first light for SOFIA, based on the expected shear layer seeing, the as-built optical performance, and 2Ó rms image motion. The blue curve represents the ultimate combined optical quality and image motion requirement (80% encircled energy in a 1.6Ó diameter circle) convolved with the expected shear layer seeing. Also plotted are representative photometry aperture diameters likely to be used for processing occultation frames under both conditions described above. The image motion assumed is larger than will be experienced when observing at high frame rates.
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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