NICMOS Instrument Handbook for Cycle 11

Expected Calibration Accuracies

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Remarks

In Table 13.1 we list a provisional summary of our calibration goals for Cycle 11. These goals represent the calibrations and performance achieved by NICMOS during Cycle 7 and 7N. Calibration proposals which will be executed during the SMOV phase and during the Cycle 11 calibration program are aimed at reproducing (and possibly improving on) the same level of calibration obtained during Cycle 7 and 7N. Although observers may plan on NICMOS achieving these levels of performance, uncertainties still exist, as explained in the next section. Science programs which require superior calibrations should request and justify additional observing time to reach the necessary calibration accuracy.

Areas of Significant Uncertainty

The figures reported in the Table 13.1 are drawn directly from the performance and calibrations achieved with NICMOS during its "cryogenic life" (Cycle 7 and Cycle 7N). Our goal for Cycle 11 and subsequent cycles is to achieve the same level of calibration accuracy obtained during Cycle 7 and 7N.

Uncertainties in the actual performance during Cycle 11 are related to the temperature stability under NCS operations on both orbital and secular timescales. Current requirements set goals of 0.1 K temperature stability on orbital scale and 0.5 K over one year. Other areas of uncertainty include the quality of the photometric transformations and (for a small portion of each Camera's field of view) the effects of vignetting.

Provisional Cycle 11 Calibration Goals

Table 13.1: Summary of Cycle 11 Calibration Goals 

Attribute	Accuracy	Limiting Factor/Notes
Detector dark current and shading	<10 DN	All MULTIACCUM sequences will have good calibrations. A small subset of the available ACCUM mode exposure times will have a direct calibration.
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	6% 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 better. Expected accuracy over central 80% of spectral range. Grism C flat field may not achieve this performance.
Astrometry	0.5% plate scale 0.1" to FGS frame	per observation, after geometric distortion correction