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42.10 Expected Accuracies of HSP Data

HSP photometric accuracies are strongly dependent on the observational setup and observing conditions, such as spacecraft jitter. Absolute photometry can be done only with a one sigma limiting accuracy of approximately 5%, but relative photometry is possible with an accuracy of 1-2%.

**Estimated HSP Calibration Accuracies**
Attribute	Estimated Accuracy	Comments
Absolute Timing	~10 millisec	Can be achieved from science headers if HST/UTC timing regression coefficients appropriate to observation date were used in post-observation calibration; otherwise, use methods from HSP ISR 12.
Relative Timing (timing resolution)	Digital modes: 10.7 microsec Analog modes: ~1 millisec	For PRISM mode: relative timing given by science headers must be corrected for format-dependent read-beam switching time (see page 42-2).
Detector stability: Detector linearity:	Sensitivity: UV1, UV2, POL all constant within 1%; VIS: factor of 3 decrease then recovery linearity: +/- 0.01 mag	1991 through summer 1993 monotonic decrease, post-August 1993 complete recovery VIS 551W for magnitude range 5.11 < V < 12.79
Absolute photometry (flux calibration)	5% (one sigma)	Limited by breathing effects and small differences in telescope pointing at different standard star observing epochs
Relative photometry	1-2%	Limited by guiding, re-acquisition centering, orbital effects (breathing, jitter)
Polarimetry: q,u,p	0.3% (one sigma) F327M and F277M	Add in quadrature with photon statistical uncertainty
Aperture Location	Absolute: <50 milliarcsec Relative: <20 milliarcsec

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42.10 Expected Accuracies of HSP Data

Attribute

Estimated Accuracy

Comments