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Overview

WFC3 offers slitless spectroscopy with both the ultra-violet/optical (UVIS) and infrared (IR) channels. The table below gives a brief summary of the WFC3 grism capabilities. Grism calibration information is linked in the grism name column.

WFC3 Spectroscopic Capabilities

 

Channel Grism Wavelength Range (nm) Resolving Power Dispersion
(nm/pixel)
Recommended
Direct Filters
UVIS G280 190-800 70 @ 300nm 1.3 F300X or F200LP
IR G102 800-1150 210 @ 1000 nm 2.45 F105W or F098M
IR G141 1075-1700 130 @ 1400 nm 4.65 F140W or F160W

 

For point sources. For extended sources, the extent of the target in the dispersion direction effectively determines the spectral resolution.

A direct image is required as part of all grism observations in order to set the wavelength zero-point. Note: these are only recommended filters. Other filters may be used if desired, but one must use the correct calibration files as indicated below.

Latest Developments

Persistence

The WFC3 IR detector is susceptible to persistence which appears as afterglow in parts of the detector that experienced high fluence (total number of photo-electrons released) in earlier exposures. Persistence is not corrected for in calwf3 or aXe. Examples of persistence and suggestions on how to mitigate it are given in the WFC3 Data Handbook.

STScI provides a persistence model for each WFC3 IR dataset through a separate persistence search form which allows users to view and download the persistence model. Search for the dataset of interest and then follow the links under "Dataset" to view the model and the links under "Visit" to download the model. A full description of the data products is provided here. A detailed description of the current modeling algorithm can be found in ISR 2015-15.

Observers and archive users are encouraged to contact the help desk if the persistence subtraction substantially limits their ability to extract science from an image or set of images.

Additional Resources

2010 STScI Slitless Spectroscopy Workshop

The 2010 workshop highlighted scientific results of slitless spectroscopy and hosted tutorials on using and analyzing data from the WFC3 Grism; the archived webcast of workshops and talks is publically accessible. 

PandExo

PandExo is a community tool and python package to generate instrument simulations of JWST (NIRSpec, NIRCam, and NIRISS) and HST/WFC3 for the purposes of transiting exoplanet science. It is publically hosted on Github.

Last Updated: 01/08/2024

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HST Help Desk 

Please contact the HST Help Desk with any questions.