Caveats of using Pandeia for Roman
The Roman module of Pandeia is still under active development. Therefore, some features might not accurately reflect the final capabilities of the observatory and these limitations are described below. There are also some known open issues with the software itself that are maintained by the developers and these are referenced here. This documentation is written for Pandeia version 2024.12 (released on December 11, 2024).
Current Limitations in Pandeia for Roman
Simplifying Assumptions for Point Spread Functions
Notional Reference Point
The Point Spread Functions (PSFs) used in Pandeia are obtained using the Roman module of WebbPSF . More information on WebbPSF can be found in the WebbPSF for Roman articles in the Simulation Tools Handbook.
For the astronomical scene, the PSF is computed at a single notional point within the WFI field of view. Thus, the field dependence of the PSF (both within a detector or from one detector to another) is not currently accounted for in these scene simulations. We suggest the user consider using STIPS , the Space Telescope Imaging Product Simulator software, or Roman I-Sim - The Roman Image Simulator for field-dependent PSF models.
Limited Area
Pandeia is primarily designed for scene calculations under 25 arcseconds on a side and that have an overall small number of objects. The PSF is pre-calculated as a finite stamp image that is 3 arcsec by 3 arcsec. While simulating larger PSFs (e.g. to account for diffraction spike contamination from bright stars) is in principle possible, it is not recommended with Pandeia . Once again, we suggest the user consider using STIPS , the Space Telescope Imaging Product Simulator, or Roman I-Sim - The Roman Image Simulator software for more flexibility in the PSF size.
Simplifying Assumptions for Detectors
Quantum Efficiency
Pandeia currently uses a single quantum efficiency curve representative of the set of 18 flight detectors. Note that the throughput can vary between 5% and 10% between the individual detectors.
The WFI detectors are currently undergoing active testing and this reflects the current best practice until better characterization is available.
Simplifying Assumptions for Astronomical Inputs
Background Models
Pandeia assumes background models identical to those of JWST, with the exception of the observatory self-emission background, which has been updated to accurately reflect the contribution from Roman. These estimates will be updated as more characterization data is available (e.g. before and after launch). The background model below 1.2 micron is known to be inaccurate and results in an overestimated zodiacal light component and hence affects the ETC results.
Open Issues in the Pandeia Software
A complete list of known issues for Pandeia can be found on the Documentation for Known Issues that is continuously updated by the Pandeia and STScI ETC team. This documentation is written for Pandeia version 2024.12 (released on December 11, 2024).
For additional questions not answered in this article, please contact the Roman Help Desk at STScI.