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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


Estimated Accuracy


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


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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Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved. Last updated: 01/14/98 16:01:49