22.1 Calibration Goals

In Table 22.1 through Table 22.5, we publish the calibration goals for Cycle 7. These are the accuracies we aim to provide to users by the end of Cycle 7 for data taken in supported modes at any time during Cycle 7. That is, at the end of Cycle 7, if you use the most up to date calstis calibration software and the most appropriate reference files to recalibrate your data, then these are the accuracies we aim to be able to provide. In the interim, as we obtain and process the on-orbit calibration data needed to produce the reference files to support this level of calibration accuracy, and as we improve the calibration software in tandem, the level of accuracy you will receive in your data will be different (lower) than these values. Information about the accuracies obtainable at any one time and about data foibles will be regularly posted to the STIS WWW page and announced in Space Telescope Analysis Newsletters (STANs) sent via E-mail to the STIS community (see below).

CCD Spectroscopic Accuracies

Attribute	Accuracy	Limiting Factors
Relative wavelengths-within an exposure	0.1-0.25 pixels	Stability of optical distortion
Absolute wavelengths-across exposures	1.0 pixels	· Thermal stability · Internal versus external illumination · Derivation of wavecal zero point
Absolute photometry	10%	Instrument stability and photometric calibration
Relative photometry (within an exposure)	5%	Instrument stability and photometric calibration

MAMA Spectroscopic Accuracies

Attribute	Accuracy	Limiting Factor
Relative wavelengths-within an exposure	0.25-0.5 pixels	Stability of small scale geometric detector + optical distortion
Absolute wavelengths-across exposures	1.0 pixels	· Thermal stability · Internal versus external stability · Derivation of wavecal zero point
Absolute photometry	15%	Instrument stability and calibration
Relative photometry (within an exposure)	5-10%	Instrument stability/flat fields

CCD Imaging Accuracies

Attribute	Accuracy	Limiting Factor
Relative astrometry-within an image	0.1 pixels	Stability of optical distortion
Absolute photometry	5-10%	Instrument stability
Relative photometry within an image	5%	External illumination pattern

MAMA Imaging Accuracies

Attribute	Accuracy	Limiting Factor
Relative astrometry-within an image	0.25 pixels	Small scale distortion stability
Absolute photometry	15%	Instrument stability and calibration
Relative photometry within an image	10%	Flat fields/external illumination

Target Acquisition Accuracies

Attribute	Accuracy	Limiting Factor
Guide star acquisition	1-2"	Catalog uncertainties
Following target acquisition exposure	0.2"	Centering accuracy plus plate scale accuracy to convert pixels to arcsecond
Following peakup acquisition exposure	30% of the slit width	Number of steps in scan + PSF