OSCIR Performance and Use

Status and availability: OSCIR has been loaned to Gemini by the University of Florida.  In semester 2001B it will be available in QuickStart service observing mode only. For target RA constraints see the instrument calendar.
Operational use: Like other mid-IR imagers and low resolution spectrographs, accurate cancellation of the sky and telescope background is most readily achieved by the technique of chopping and nodding. The small field of view (11 arcsec) and constraints of tip-tilt image motion compensation means that the source must be chopped off the detector; no on-chip chopping is available. See the telescope characteristics for more details of the chopping performance.
Elements of OSCIR: Specific elements of OSCIR include:
  • Detector - a raw image of the uniformly illuminated detector shows the good cosmetic quality (~10 bad pixels) of the 128x128 pixel device.
  • Filters
  • Gratings, slits and spectral resolution
  • Wavefront sensors (WFSs) and guide stars
    • The Peripheral WFS (PWFS) is required for image motion stabilisation (in one half of the chop cycle) whilst chopping. Note the restrictions on guide star magnitude.
Sensitivity: A preliminary guideline sensitivity table is available.

The estimated image quality delivered to the instrument is given as part of the observing condition constraints.

Calibration: A set of recommended mid-IR standard stars is available.
Observing overheads: Recent results indicate that each new target will incur a configuration overhead of 15 minutes (e.g. to set the peripheral wavefront sensor(s) for aO and tip-tilt correction) and an additional 15 minutes for basic calibration. Once on target, a typical observation with chopping and nodding means that about 25% of the time is spent observing the source (this includes the chop and nod overheads with the nominal 88% chop duty cycle and 15 arcsec chopping at 3Hz). Thus an on-source integration of 30 minutes would take about 2 hours. It is not possible to chop on-chip We are working to reduce these overheads.
Data processing and software: The raw data are 6-dimensional FITS files (see a description of the OSCIR data format). An OSCIR package of IRAF scripts has been released as part of the Gemini IRAF package.

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Last update February 19, 2001; Phil Puxley