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Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 22 > Chapter 16: Accuracies > 16.1 Summary of Accuracies

16.1
In this chapter we describe the accuracies for STIS photometric, spectral, and astrometric calibration achieved in the close-out calibration of data obtained up to the suspension of STIS operations early in Cycle 13. It is anticipated that similar accuracies will be obtainable with a repaired STIS.
Table 16.1 through Table 16.5 list the accuracies for each of STIS’ basic observation modes: CCD spectroscopy, MAMA spectroscopy, CCD imaging, MAMA imaging, and target acquisition. The pixels in the tables for the MAMA detectors are low-resolution pixels. All accuracies quoted are 2-sigma limits. The accuracies reflect our current understanding of STIS as of August 2010 and are those we expect in the data that has been delivered to the archive for the STIS close-out calibration. The sources of inaccuracy are described in Chapter 4 of the STIS Data Handbook, which includes in-depth discussions of instrumental phenomena and the creation of reference files that characterize those phenomena.
Many significant changes in pipeline calibration have been made since the last edition of this Handbook was published in October 2003; see Chapter 3 of the STIS Data Handbook for details. Extracted spectra and rectified spectral images from all STIS detectors are now corrected for time-dependent and temperature-dependent variations in sensitivity (see also STIS Data Handbook 5.4.1). Extracted CCD spectra are corrected for CTE losses and are adjusted for the formerly neglected interdependence of grating and aperture throughputs. Time-dependent rotation of spectral traces is applied to the most commonly used first order modes during spectral extraction and spectral image rectification. The blaze shift correction has recently been substantially improved for echelle spectral extractions, and echelle flux calibration has also recently been improved. Improvements were made to flat-field reference files (STIS Data Handbook Section 4.1.4).
We remind you that calibration data have always been immediately non-proprietary. If you have need for extreme accuracy or urgent results, you may wish to consider direct analysis of the calibration data for your particular observing mode. (See also Chapter 17 for a description of our on-orbit calibration program.)
Table 16.1: CCD Spectroscopic Accuracies
Absolute photometry1,2,3
L modes4
M modesd
Relative photometrya,b
(within an exposure)
L modesd
M modesd
1
Assumes star is well centered in slit. See the STIS Data Handbook for a more complete description of the impact of centering on accuracies.
2
Assumes use of a 2 arcseconds wide photometric slit. See the STIS Data Handbook for a fuller description of the impact of slit width on photometric accuracy.
3
Photometric accuracies referenced are for continuum sources; equivalent width and line profile measures are subject to other uncertainties (such as spectral purity and background subtraction).
4
This accuracy excludes the G230LB and G230MB modes when used with red targets, for which grating scatter can cause large inaccuracies in the flux calibration; see Gregg et al., (2005 HST Calibration Workshop) available at URL http://www.stsci.edu/hst/
HST_overview/documents/calworkshop/workshop2005/papers/gregg.pdf
).

Table 16.2: MAMA Spectroscopic Accuracies
0.5–1.0 pixel1
1
A pixel for the MAMA refers to 1024 1024 native format pixels.
2
Assumes star is well centered in slit.
3
Assumes use of a wide photometric slit.
4
For 0.2X0.2 arcsecond slit. These are typical accuracies which can be 2 to 3 times better or worse as a function of wavelength (see STIS ISR 1998-18 for details).

Table 16.3: CCD Imaging Accuracies
Table 16.4: MAMA Imaging Accuracies
0.25 pixel1
1
A pixel for the MAMA refers to 1024 1024 native format pixels.

Table 16.5: Target Acquisition Accuracies
1-2
0.2-0.3


0.01

0.01–0.1

Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 22 > Chapter 16: Accuracies > 16.1 Summary of Accuracies

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