CALWF3 Pipeline Processing

Data downloaded from the Mikulski Archive for Space Telescopes (MAST) is processed on the fly by the calwf3 pipeline with the most recent calibration files. Users generally should not need to reprocess their data. The links below provide more information on the pipeline.

WFC3 Pipeline

A brief description of the calwf3 reduction, and its recent updates, is provided here. A more detailed description is available in the WFC3 Data Handbook and in the wfc3tools package documentation.

WFC3 Reference Files

The most recent individual calibration files for WFC3 are available from the Calibration Reference Data System. These files are used by calwf3 and Astrodrizzle. Reference files can also be retrieved from MAST or downloaded directly from the iref directory.

HSTaXe Spectral Extraction

The calwf3 processing of the grism observations does not include extraction or calibration of the spectra. This must be done off-line using additional tools. The current software supported by STScI is hstaxe which is a complete Python implementation of the Spectral Extraction and Visualization Software (aXe). HSTaXe has the same functionalities as aXe but, unlike aXe, does not require IRAF/PyRAF (no longer supported by STScI). HSTaXe can be used for the calibration and automatic extraction of large numbers of spectra from HST slitless spectroscopic observations.


Please find the most up-to-date installation information here.

Data Reduction

The WFC3 IR Grism Cookbook is a step-by-step guide to reducing G141 IR grism data using aXe. The procedures described in the Cookbook are directly applicable to the G102 grism with small modifications. The grism data from the WFC3 ERS Program used as an example in the Cookbook is also available for download.

Two more Cookbooks exist for reducing UVIS grism data, as described in ISR 2023-07. They address spectral extraction for UVIS full-frame and subarray data separately:

  1. Spectral extraction with full-frame data from WFC3’s UVIS channel, and
  2. Spectral extraction with subarray data from WFC3/UVIS


The configuration and calibration files used with the hstaXe software are available for download below. The download for each grism includes sensitivity, flat-field cube, and configuration files for different direct filter - grism combinations. To use these calibration products with hstaXe, copy them into a local directory and set your AXE_CONFIG_PATH environment variable to point to that directory. No further re-formatting is needed.

G280 UVIS Grism

Download current calibration files: 

For more information on the derivation of G280 calibration files, as well as individual file downloads:

WFC3 G280 Calibrations

G102 IR Grism

Download current calibration files: 

For more information on the derivation of the G102 calibration files as well as individual file downloads:

WFC3 G102 Calibrations


G141 IR Grism

Download current calibration files: 

For more information on the derivation of the G141 calibration files as well as individual file downloads:

WFC3 G141 Calibrations


Zeropoints for WFC3 Filters

The zeropoint of the reference image filter is required by aXeSIM and aXe in the *.cat files:

WFC3 IR and UVIS zero-points



Note: aXe and aXeSIM only accept ST and AB MAG zero-points.

IR Grism Sky

Sky images have been provided for both G102 and G141, however the single images used by aXe do not take into account the full complexity of the sky background of grism observations. A more accurate background subtraction can be achieved by using separate images for each of the background components: zodiacal light, He I emission and scattered light (for G141). Further information and downloads are available on the WFC3 IR grism sky page and in ISR 2015-17The use of the new sky images has not been implemented in aXe.

To take advantage of the new sky images, users are encouraged to follow the algorithm described in the appendix of ISR 2015-17.


UVIS Grism Sky

The G280 sky calibration frames should be applied to data processed with calwf3 v3.4.1 or later. ISR 2023-06 provides details of how these sky frames, which are normalized to 1, were created. These calibration frames can be used as input in the HSTaXe spectral extraction software (please see the G280 extraction cookbook.)

Further information and downloads are available on the WFC3 UVIS grism sky page

Additional Resources


LINEAR is a suite of IDL & C routines designed to simulate & extract WFC3/IR grism spectroscopy, ideally taken at multiple positions/orients. See Ryan, Casertano, & Pirzkal 2018 for more details on the implementation, verification, and improvements. Most packages extract spectra for individual ORIENTs and stitch the contamination-corrected 1-d spectra (for each roll angle) post facto. This is the fundamental distinction with LINEAR, where we attempt to solve for the non-parameteric spectrum that best fits the entire canon of available dispersed images (that may be rotated or dithered with respect to each other).  Example usage of the code is described by Ryan, Casertano, Pirzkal 2018 and  ISR 2018-13.


Wayne is a WFC3 IR Grism Spectroscopy simulator described in Varley & Tsiaras (2015). It can simulate both staring and spatial scanning observations, and is publicly hosted on Github.


A Grism H-alpha SpecTroscopic (AGHAST) survey, led by Ben Weiner, obtained G141 grism observations in GOODS-N.


The WFC3 Infrared Spectroscopic Parallel Survey (WISPS) is a pure-parallel WFC3 survey which has obtained IR grism observations in over 1000 random fields. The current data release provides access to reduced and drizzled direct near-IR imaging (F110W, F140W, & F160W), direct UVIS imaging (F475X & F600LP), and the near-IR grism spectra (G102 and G141).


The 3D-HST Survey was a spectroscopic galaxy evolution survey with HST. 3D-HST obtained G141 grism spectroscopy over four of the five CANDELS fields (AEGIS, COSMOS, GOODS-S and UDS). HST and ground-based images, photometric catalogs and grism spectra for all five CANDELS fields are available for download from the team website. The data reduction pipeline employed by 3D-HST is described in Momcheva, van Dokkum, Brammer et al. (2015).

Last Updated: 03/06/2024


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