Observatory Support
STScI Exposure Time Calculators Oversight

STIS Grating Summary

¹ Resolution of up to 200,000 may be obtained when using this grating with the 0.1 X 0.03 aperture and specialized data reduction techniques.

For gratings with more than one supported central wavelength value, the user is also allowed to choose which central wavelength to use for the calculation. Whenever the grating or central wavelength value is changed, the wavelength value which specified in section 2 as the wavelength for at which the calculation is to be performed is checked to see if it is within the valid range for that grating and cental wavelength value. If the wavelength specified here is out of the allowed range, then its value is reset to the mid-point wavelength of the allowed range. Users should check this value carefully, as the value already in this field may depend on prior selections made in the web interface.

To simplify instrument operation and calibration, only specific grating tilts with corresponding central wavelengths are implemented. There are also a few unsupported or unavailable central wavelengths.

Approximate wavelength solutions for the prism settings at 1200 and 2125 Å are available.

Issues to consider when choosing between G230LB and G230L or choosing between G230MB and G230M include relative sensitivity, read noise, plate scale, bright object limits, and detector PSF.

G750L and G750M are subject to long wavelength fringing for wavelengths > 7500 Å.

Spectral format plots for each combination of detector, optical element and central wavelength are available.

Only a portion of the full spectral range falls on the detector for the intermediate-resolution first-order and the echelle (except E140M) gratings. Therefore separate exposures must be taken for these gratings for full wavelength coverage.

STIS Filter Summary

¹red halo

²red leak

³The 50CORON aperture is an unfiltered aperture with a number of occulting bars and wedges which functions as a coronagraphic mask. A number of separate aperture positions have been defined for use within 50CORON, ad may be individually specified in Phase 2 proposals.

⁴not well focused

⁵excludes O I 1302

⁶excludes Ly-alpha

⁷high airglow

⁸low throughput

Note that MAMA imaging observations are subject to especially strict bright object limits, and will not be performed unless ALL objects in or near the aperture can be shown to be below these limits.

As STIS filters are located in the STIS slit wheel they must be listed as apertures in Phase II proposals and cannot be used in combination with other apertures. The STIS filters can, however, be used together with a grating to do filtered slitless first order spectroscopy. This can be especially useful when it is necessary to exclude contamination due to geocoronal lines.

STIS has a relatively limited set of filters. However its imaging capabilities do include some unique advantages that make it worth considering as an alternative to WFPC2 or ACS for some UV and optical imaging projects.

Comparisons of Imaging Mode Throughputs:

• CCD, FUV-MAMA and NUV-MAMA Clear and Filtered Throughputs
• STIS CCD Clear vs. WFPC2
• STIS vs. ACS Imaging
• Color Corrections from Johnson V to AB Magnitude

Choosing a filter for imaging observations or slitless spectroscopy:

• CCD Ghosts and Reflections
• CCD Red Light Halo
• Filter Choice for Target ACQ Observations
• Other Caveats for STIS Imaging
• MAMA Longpass Filters and Geocoronal Lines
• MAMA Imaging Bright Object Limits
• STIS Imaging, Spectroscopic, and Target ACQ ETCs