Pandeia for Roman
Pandeia generates simple astronomical scenes from which the signal-to-noise can be computed and serves as the Exposure Time Calculator (ETC) for the Roman Space Telescope Wide Field Instrument (WFI).
Pandeia Description
Pandeia is the backend software used for the Exposure Time Calculator (ETC) system developed for the James Webb Space Telescope (JWST) and the Nancy Grace Roman Space Telescope (Pontoppidan et al. 2016). It is based on a Python engine that calculates three-dimensional data cubes from a library point spread functions (PSFs) pre-computed with WebbPSF . These cubes are then projected onto a detector plane given an instrument configuration, and a 2D signal-to-noise map is extracted. This allows for handling of realistic PSFs, Multi Accumulation detector readouts stored in "MA Tables", correlated detector readnoise, dithering, and multiple photometric and spectroscopic extraction strategies.
Pandeia is designed to guide the user toward the best exposure parameters for a given science case and observing setup. The software performs a scene simulation that is used to compute the signal-to-noise achievable given the astronomical input and observational setup. The user can input both point sources and extended sources, where the latter are modeled with Sérsic profiles. The Figure of Example Astronomical Scenes from Pandeia provides an example of a simulation aimed at estimating the signal-to-noise achievable in the detection of a supernova given its location in the host galaxy. The astronomical scene contains a both a point source and an extended source. Pandeia is not designed to create fields of view wider than ~75 arseconds on a side nor multi-detector images. For the simulation of large field of views or multi-detector images, we suggest users to consider the STIPS Space Telescope Imaging Product Simulator software.
Currently, Pandeia computations for Roman are only available by installing the Pandeia package, examples are given in the Pandeia Tutorials article. In the future, a web tool will offer streamlined functionality for quick use.
Figure of Example Astronomical Scenes from Pandeia
An example of an astronomical scene created by Pandeia . In this example, a high-redshift galaxy, modeled using a Sérsic profile, and a superimposed supernova, modeled as a point source, are simulated in each of the eight imaging elements for the Wide Field Instrument (WFI) (from top row from left: F062, F087, F106, F129 and bottom row from left: F146, F158, F184, F213). A description of the optical elements for Roman is given in the WFI Optical Elements article in the WFI Imaging Mode User Guide.
Current Software Version
This documentation is written for Pandeia version 3.1 (released on December 11, 2023). Pandeia can be installed via the Python Package Index (pip):
pip install pandeia.engine==3.0
Pandeia requires additional reference data, which can be obtained from the general Pandeia Engine Installation article.
Pandeia for Roman Documentation
The contents of the user guide for Pandeia are as follows:
Pandeia for JWST Documentation
Pandeia has been thoroughly documented for use with JWST and Roman users may find this documentation useful. The relevant JDox documents can be found here:
While Pandeia for JWST can be ran via an user interface (JWST ETC web UI), Pandeia computations for Roman are only available by installing the Pandeia package, examples are given in the Pandeia Tutorials article. In the future, a web tool will offer streamlined functionality for quick use.
For additional questions not answered in this article, please contact the Roman Help Desk at STScI.
References
- The JWST Documentation (JDox) website.
- "Pandeia: a multi-mission exposure time calculator for JWST and WFIRST", Pontoppidan et al. 2016