4.2 Summary of Accuracies

In Table 4.1 through Table 4.5, the accuracies are listed for each basic observation mode of the STIS: CCD spectroscopy, MAMA spectroscopy, CCD imaging, MAMA imaging, and target acquisition. The MAMA pixels in these tables are low resolution pixels. All accuracies quoted are 2σ limits, and reflect our current understanding of STIS calibration. Any updates to these accuracies will be documented in Chapter 16.1 of the STIS Instrument Handbook. The main sources of inaccuracy are discussed in some detail in the next subsections.
We remind users that calibration data are, and have always been, made non-proprietary immediately after they are (or were) taken. If higher accuracy or urgent results is needed, one may wish to consider direct analysis of the calibration data for the particular observing mode (see also Chapter 17 of the STIS Instrument Handbook for a description of our on-orbit calibration program).

Table 4.1: CCD Spectroscopic Accuracies

¹ For more recent analyses of wavelength accuracy, see STIS ISR 2011-01 and STIS ISR 2015-02. Note that the wavelength accuracies will also depend on the accuracies of the rest wavelengths used in calculating the dispersion relations

 ² Assumes star is well centered in slit, and use of a 2 arcseconds wide photometric slit. 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., (2006). 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).

Table 4.2: MAMA Spectroscopic Accuracies

¹ For more recent analyses of wavelength accuracy, see STIS ISR 2011-01 and STIS ISR 2015-02. Note that the wavelength accuracies will also depend on the accuracies of the rest wavelengths used in calculating the dispersion relations
² A pixel for the MAMA refers to 1024 × 1024 native format pixels.
³ Assumes star is well centered in slit, and 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).
⁵ Quoted relative flux accuracies of echelle spectra assume that the time dependent shifts in the echelle blaze function are properly corrected. Recent improvements to the blaze shift correction yield agreement in the order overlap regions to better than 5% for E140H (see August 2017 STAN).

Table 4.3: CCD Imaging Accuracies

Table 4.4: MAMA Imaging Accuracies

¹ A pixel for the MAMA refers to 1024 × 1024 native format pixels.
² A recent re-analysis of the FUV-MAMA geometric distortion has yielded rms residuals of 4 mas (0.16 pix) in each coordinate, compared to the positions in an astrometric standard catalog based on WFC3/UVIS imaging data (see STIS ISR 2018-02).

Table 4.5: Target Acquisition Accuracies