9.5 Specific Tools for the Analysis of WFC3
This section describes existing tools and packages that can be used for the analysis of WFC3 data. Some of these tools are distributed as STScI affiliated packages, while others have been developed by STScI scientists for their own scientific projects, but have also been made available to the community. The latter type of software is not directly supported by the WFC3 team; thus users are directed to the software developers for assistance.
wfc3tools is a python package containing several WFC3-specific tools. Online documentation for wfc3tools can be found on read the docs at:
The package is available on github and is also distributed on the STScI-maintained AstroConda channel. wfc3tools contains the python wrapper modules that call the calwf3 pipeline executables (whose source code is written in C), as well as other auxiliary functions. The pipeline modules (calwf3, wf3cte, wf3ccd, wf32d, wf3rej, wf3ir) are described in detail in Chapter 3 of this book. Here we briefly describe the other tools. The boldface paragraph titles correspond to the module name, and link to the read-the-docs resources which contain a more detailed documentation.
Given an image specified by the user which contains a subarray readout, return a full-frame image with the subarray implanted at the appropriate location.
Plot statistics for a specified image section up the ramp of an IR MultiAccum image. Sections from any of the SCI, ERR, DQ, image extensions can be plotted. A choice of mean, median, mode, standard deviation, minimum and maximum statistics is available.
Plot the stack of MultiAccum sample values for a specified pixel in an IR multiaccum image. Pixels from any of the SCI, ERR, DQ, or TIME image extensions can be plotted.
Sampinfo prints information about a WFC3/IR MultiAccum image, including exposure time information for the individual samples (readouts). The global information listed (and the names of the header keywords from which it is retrieved) includes:
- the total number of image extensions in the file (NEXTEND)
- the name of the MultiAccum exposure sample sequence (SAMP_SEQ)
- the total number of samples, including the “zeroth” read (NSAMP)
- the total exposure time of the observation (EXPTIME).
Given an image specified by the user which contains a subarray readout, return the location of the corner of the subarray in a full frame reference image (including the full physical extent of the chip), in 1-indexed pixels. If the user supplies an X and Y coordinate, then the translated location of that point will be returned.
9.5.2 Standalone Fortran routines for CTE correction
While the WFC3 team provides a python tool, wfc3cte, under the wfc3tools package, a standalone routine for cte correction of raw UVIS images is also available and documented here:
9.5.3 Cross-talk correction software
As described in Section 5.5.3, electronic crosstalk between the UVIS amplifiers during readout induces faint, negative, mirror-symmetric ghost images in the other quadrant of the same CCD chip. Software for cross-talk removal as well as a description of the analysis behind such software can be found here:
9.5.4 Grizli: Grism redshift & line analysis software for space-based slitless spectroscopy
Grizli is not official WFC3 software but has been developed by WFC3 scientists. It is intended to provide some general techniques for manipulating HST slitless spectroscopic observations, providing software kernels to address questions such as: "How does the WFC3/IR G141 grism disperse the spectrum of a star/galaxy at pixel position (x,y) in my F140W direct image?".
Grizli, with examples and documentation can be found on github.
9.5.5 PandExo: A community tool for transiting exoplanet science with JWST & HST
PandExo is not official WFC3 software, but WFC3 scientists have made significant contributions to its development. Similar to an exposure time calculator (ETC), PandExo is a transiting exoplanet noise simulator. It is based on Pandeia, the ETC for JWST, and has been expanded to include HST's WFC3 instrument.
PandExo, with examples and documentation can be found on github.
9.5.6 IDL procedures for simulating trajectories of multi-lined spatial scans
The WFC3 ISR 2017-06 describes simulations of spatial scans using a simple physical model of HST motions. The document contains an IDL code in the appendix that can be used both in designing detailed WFC3 observation in spatial scan mode, as well as for analyzing existing ones.
9.5.7 Satellite Trails Detection
The ACS instrument team has developed a code for finding satellite trails in their data, and flagging the interested pixels’ DQ extension accordingly. The software is part of the acstools package and the detailed documentation be found here:
Flagging such trails can be useful e.g., in combining multiple images with Astrodrizzle. Disclaimer: the software is developed and tested only for ACS data, but should work on WFC3 data as well.
9.5.8 LINEAR: IDL and C tools for grism spectroscopy
LINEAR is a suite of IDL and C codes to extract and simulate slitless spectra for WFC3/IR observations with multiple roll angles. The details will be described in Ryan, Casertano, & Pirzkal, 2018, LINEAR: A Novel Algorithm for Reconstructing Slitless Spectroscopy and users are welcome to contact the authors with questions.
9.5.9 Code for mitigation of variable IR background
WFC3 ISR 2016-16 illustrates some possible strategies for dealing with IR variable background due to the HeI atmospheric line at 1.083. The ISR provides a full description of the methods, and the code is available at:https://github.com/gbrammer/wfc3/blob/master/reprocess_wfc3.py
WFC3 Data Handbook
- • Acknowledgments
- Chapter 1: WFC3 Instruments
- Chapter 2: WFC3 Data Structure
- Chapter 3: WFC3 Data Calibration
- Chapter 4: WFC3 Images: Distortion Correction and AstroDrizzle
- Chapter 5: WFC3-UVIS Sources of Error
- Chapter 6: WFC3 UVIS Charge Transfer Efficiency - CTE
Chapter 7: WFC3 IR Sources of Error
- • 7.1 WFC3 IR Error Source Overview
- • 7.2 Gain
- • 7.3 WFC3 IR Bias Correction
- • 7.4 WFC3 Dark Current and Banding
- • 7.5 Blobs
- • 7.6 Detector Nonlinearity Issues
- • 7.7 Count Rate Non-Linearity
- • 7.8 IR Flat Fields
- • 7.9 Pixel Defects and Bad Imaging Regions
- • 7.10 Time Variable Background Contamination
- • 7.11 IR Photometry Errors
- • 7.12 References
- Chapter 8: Persistence in WFC3 IR
- Chapter 9: WFC3 Data Analysis
- Chapter 10: WFC3 Spatial Scan Data