Space Telescope Science Institute  Chapter 13:  Calibration Goals and Plans  13.2 Calibration Plans

13.1 Calibration Accuracies


In Table 13.1 we summarize the calibration goals for Cycle 13. Observers with science programs that require better calibrations should request and justify additional observing time for any supplemental calibrations necessary to achieve their goals.

The calibration proposals that have been executed during the SMOV phase, as well as the ones included in the Cycles 10, 11 and 12 calibration programs, were aimed at reproducing and possibly improving the level of calibration accuracy achieved during Cycle 7 and 7N.

The actual performance of NICMOS is closely related to the temperature stability under NCS operations. Results based on the first 14 months of operations indicate very good stability (rms fluctuations ~ 0.07 K) and, therefore, the accuracies quoted in Table 13.1: should be reached.


Table 13.1: Summary of Cycle 13 Calibration Goals 
Attribute
Accuracy
Limiting Factor/Notes
Detector dark current and shading
<10 DN
All MULTIACCUM sequences will have good calibrations.
Flat fields
1% broad-band
3% narrow-band
Color and temperature dependence may limit flats in some cases.
The low spatial frequency may only be reliable to 3%.
Photometry
3%1 photometric zero point
2% relative over FOV
2% stability
Photometric systems, Intrapixel effects, Filter leaks on red sources, Temperature stability
PSF and focus
Maintained within 1 mm (except for NIC3 which will be ~ 4mm off nominal best focus.)
Breathing and OTA desorption are approximately equal effects. Cold-mask shifting affects PSF shape.
Coronagraphic PSF
0.013 arcsec accuracy positioning in the hole

GRISM wavelength calibration
.005 µm
Limited by centroiding of target for wavelength zeropoint determination.
GRISM photometric calibration
~30% absolute and relative
The figure is quoted without the NIC3 intrapixel sensitivity correction. With this correction, GRISM photometry will be significantly better (within a few percent).
Expected accuracy over central 80% of spectral range.
Grism C flat field may not achieve this performance.
Polarimetry
1%
Polarization uncertainty may be dominated by residual flat field errors.
Astrometry
0.5% plate scale
0.1" to FGS frame

per observation, after geometric distortion correction



1This is an estimate for most of the wide and medium band filters. Larger uncertainty can be expected for the narrow and very red filters. See further details in Bohlin, Dickinson, and Calzetti (2001, AJ, 122, 2218).


Chapter 13:  Calibration Goals and Plans  13.2 Calibration Plans
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