Throughput with STIS

Throughput is defined as the end-to-end effective area divided by the geometric area of an unobstructed 2.4 meter aperture.

STIS Integrated System Throughput Curves

Mode Detectors Optical Elements
Imaging CCD All Visible filters
Imaging NUV-MAMA All NUV filters
Imaging NUV-MAMA MgII vs. CN270
Imaging NUV-MAMA CIII vs. CN182
Imaging FUV-MAMA All FUV filters
Imaging FUV-MAMA LyA vs. (Clear-SrF2)
Spectroscopy All Low Resolution Gratings
Spectroscopy All All Gratings

 

Throughput curves linked above typically have 5% accuracy.

In imaging mode, unfiltered STIS throughput exceeds WFPC2 throughput. For visible light imaging, ACS should have better throughput than STIS.

Visible light throughput curves for unfiltered STIS MAMA detectors show that the FUV-MAMA is effectively solar blind, though long wavelength contamination in cool stars can be significant in imaging mode.

Updated throughput estimates for CCD imaging modes (unfiltered and F28X50LP) were implemented in the pipeline on 2001-Jul-11.

 

Change to CCD Imaging Throughput Calibration

A significant change has been made to the adopted flux calibration for STIS/CCD imaging modes. The overall throughput of the STIS/CCD/MIRVIS combination as a function of wavelength has been changed as detailed in the table below. At the same time, the relative throughput of the F28X50LP filter has been increased by about 25% over most of its wavelength range.

 

Wavelength New/Old Throughput
1500 1.012
2625 1.014
3750 1.016
5008 0.940
6808 0.873
8608 0.833
10408 0.824

 

Note that this new calibration gives our best estimate of the infinite aperture throughput for STIS/CCD imaging modes. Scattered light in the CCD at wavelengths greater than 8000 Angstroms causes aperture corrections to depend very strongly on the spectral energy distribution of the observed target. Sample aperture corrections for 50CCD and F28X50LP observations are given below. A STIS Instrument Science Report giving a full description of the absolute calibration of STIS imaging modes should be available in the near future.

Spectral Type Aperture Radius Used for Photometry (CCD Pixels)
  5 10 20 5 10 20
  50CCD Aperture Corrections (mags) F28X50LP Aperture Corrections (mags)
B -0.18 -0.10 -0.06 -0.21 -0.12 -0.08
F -0.20 -0.13 -0.09 -0.24 -0.16 -0.11
M -0.33 -0.24 -0.17 -0.35 -0.25 -0.19

 

New calibration reference files reflecting these changes have been delivered for use in pipeline processing. The only effect of these changes on calibrated STIS files will be different values for the PHOTFLAM keyword. New throughput files have also been delivered for use in SYNPHOT. Users of SYNPHOT should ensure that they obtain the updated files.

Note that these changes have no effect on the absolute flux calibration of STIS spectroscopic modes.

 

LAST UPDATED: 06/11/2019

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