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17.5 Calibration Goals

The Cycle 7 calibration goals for NICMOS are listed in Table 17.1 below. Since NICMOS is expected to run out of cryogens between the end of 1998 and the beginning of 1999, these represent the final calibration goals for the instrument. The main limiting factor for attaining such goals will be the thermal stability of the instrument. The Table summarizes the accuracy we expect to achieve for reference files, photometry, astrometry, etc. (see the NICMOS Instrument Handbook).

**NICMOS Calibration Goals**
Attribute	Accuracy	Comments/Limiting Factors
MULTIACCUM and ACCUM darks	10 ADU	All three detectors. All the supported MULTIACCUM sequences and a subset of ACCUM exposure times will be calibrated to this accuracy. Other ACCUM exposure times will require interpolation.
Flatfields	2% global uncertainty <1% pixel-to-pixel	NIC1 and NIC2 (reduced program for NIC3). Flatfields will be obtained from a combination of internal lamp flats (1% accuracy, polarizers, broad and medium band filters) and Earth flats (2% acccuracy, narrow band filters). Color dependence may limit flatfields in some cases.
Photometry	5-10% absolute 2% relative over field-of-view 2% stability	Main limiting factors: accuracy of standards; filter leaks on red sources
Focus position	maintained within 1 mm	Instrument focus will be monitored throughout the entire Cycle 7 in all three cameras
Polarizers	1% relative photometry 3-5% absolute polarization	Instrumental polarization and zero position angle of NIC1 and NIC2 will be measured. Limiting factors: dark and flatfield uncertainties; polarizing efficiency.
Grisms	0.01 µm (wavelength calibration) 20%-30% (absolute and relative photometric sensitivity)	Expected accuracy over central 80% of spectral range. Grism C flat may not achieve the declared accuracy.
Coronagraph	0.019" positioning	Hole and detector are not at common focus
NICMOS to FGS astrometry	0.1"
Plate Scale Calibration	0.2%

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stevens@stsci.edu

17.5 Calibration Goals

Attribute

Accuracy

Comments/Limiting Factors