Welcome to the WebbPSF documentation written for the Roman Space Telescope! In this series of articles, we provide users with a high-level view of the tool, its capabilities and limitations, as well as some use cases and tutorials. 

What is WebbPSF for Roman 

WebbPSF is a Python package that simulates point spread functions (PSFs) for both the James Webb Space Telescope and the Nancy Grace Roman Space Telescope. Using a set of pre-computed Optical Path Difference (OPD) maps, the tool simulates PSFs for various instrument configurations. For Roman, two modes are supported: the Wide Field Instrument (WFI), based on recent optical models from NASA's Goddard Space Flight Center, including field- and wavelength-dependent aberrations, and a preliminary version of the Coronagraph Instrument based on the Shaped-pupil Coronagraph early design.

See the Introduction to the WFI article for more information on the instrument.

Installation

WebbPSF Software Version 

This documentation is written for  WebbPSF version 2.0. Note that as of version 1.2.1, Python 3.9 or higher is required.

WebbPSF is run locally and installation of the software is straightforward when using pip. 

pip install webbpsf

The main dependency of WebbPSF is POPPY (Physical Optics Propagation in PYthon), a highly flexible package that simulates physical optical propagation including diffraction. Other major dependencies include:

• NumPy, a package for scientific computing with Python
• SciPy, a package containing algorithms for scientific computing with Python
• MatPlotLib, a library for Python visualizations
• AstroPy, the community built core package for Astronomy in Python

All the required dependencies are installed by default when the user installs WebbPSF .  Although optional, SYNPHOT is highly recommended in order to enable the simulation of PSFs with realistic source spectra. 

Input Data

Note that  WebbPSF also requires input data for its simulations, including optical path difference (OPD) maps, filter transmission curves, and coronagraph mask shapes. In addition, the environment variable webbpsf_path must also be set to point to the directory where the WebbPSF data is stored. These data files are not included in the source distribution and must be downloaded manually; detailed steps for installation, the associated data, and setting up the environment variables can also be found in the readthedocs documentation.

Users interested in running the development version of WebbPSF and/or contributing to its ongoing development may also clone or fork from the main GitHub repository.

Additional Resources

Interested users will want to refer to the readthedocs documentation.

The source code and other relevant information can also be found on the GitHub repository.

For additional questions not answered in this article, please contact the Roman Help Desk at STScI.

References

In addition to this documentation, WebbPSF is described in the following references. Users are encouraged to cite one of these publications:

1. Perrin et al. 2014, “Updated point spread function simulations for JWST with WebbPSF”, Proc. SPIE. 9143

2. Perrin et al. 2012, “Simulating point spread functions for the James Webb Space Telescope with WebbPSF”, Proc SPIE 8842

3. Perrin 2011, "Improved PSF Simulations for JWST: Methods, Algorithms, and Validation", JWST Technical report JWST-STScI-002469