The Roman Interactive Sensitivity Tool (RIST)

The Roman Interactive Sensitivity Tool (RIST)#

Kernel Information and Read-Only Status#

To run this notebook, please select “Roman Research Nexus {VERSION}” kernel at the top right of your window. For example “Roman Research Nexus 2026.1”.

This notebook is read-only. You can run cells and make edits, but you must save changes to a different location. We recommend saving the notebook within your home directory, or to a new folder within your home (e.g. file > save notebook as > my-nbs/nb.ipynb). Note that a directory must exist before you attempt to add a notebook to it.

Introduction#

Roman Interactive Sensitivity Tool (RIST) is a simulation tool designed to help users quickly explore the feasibility of observations for the Wide Field Instrument (WFI). RIST is a simplified version of the Exposure Time Calculator engine Pandeia – it uses a pre-computed grid of exposure time calculations with Pandeia that sample a set of exposure parameters and observing setups.

RIST provides users an estimate of signal-to-noise ratio (SNR) based on their selections of source brightness, spectral energy distribution (SED) type, multi-accumulation (MA) tables, and backgrounds, while using a single on-axis point source. For the details of the selections, see Notes below.

Requirements#

RIST depends on a number of modules to run. A comprehensive list of these modules and how they are utilized are listed below:

  • NumPy for numerical computing

  • pandas to read and load the pre-computed pandeia grid

  • bokeh for the interactive plotting

  • xarray to provide RIST an N-dimentional array as a structure of the pre-computed pandeia grid

  • SciPy to interpolate RIST’s xarray grid.

  • Pandeia is the Exposure Time Calculator for Roman and is used to compute a grid that samples a set of parameter space. Pandeia uses the following modules:

    • astropy

    • photutils

    • synphot

    • stsynphot

Setting up variable to allow webview in local runs

import os
if 'BOKEH_ALLOW_WS_ORIGIN' not in os.environ:
    os.environ['BOKEH_ALLOW_WS_ORIGIN'] = '*'
    print("BOKEH_ALLOW_WS_ORIGIN set to *")

BOKEH_ALLOW_WS_ORIGIN set to *

Import#

RIST is designed to work within a Jupyter notebook cell with an import of the plot_rist module. Execute the cell below to start using RIST.

from plot_rist import plot_rist
Loading BokehJS ...

Notes#

  • RIST assumes a point source target. For extended sources, please use Pandeia for more accurate results.

  • Among the 18 detectors of WFI, all calculations were done for WFI01. More information on the detectors can be found here.

  • RIST uses canned backgrounds that are pre-computed using the Roman Background Tool at the locations that are representative of the 3 Core Community Surveys footprints. More information on the canned backgrounds can be found under Pandeia Engine & Roman Interactive Sensitivity Tool (RIST) section in Assessing Background Levels for WFI Observations for the details.

    • The background is set to the medium level for all locations.

  • Multi-accumulation (MA) tables describe the sequence of individual reads that are combined into resultants and that comprise the up-the-ramp simplaing during a single exposure of the WFI detectors. The MA tables currently available in RIST are based on the Roman Design Reference Mission, and are thoroughly documented on RDox.

    • MA table naming convention: obs mode_exp time_# of resultants. ‘_s’ at the end of the name indicates ‘sparse fields only’

      • obs mode is either ‘im’ for the imaging or ‘sp’ for the spectroscopic mode (currently not supported by RIST), respectively.

      • exp time is the effective exposure time in seconds

      • # of resultants is the number of samples up-the-ramp that will be downlinked from the telescope

    • As of the R2025.9 release, RIST no longer supports truncation of the MA tables, as it may result in undesirable effects on the data and observations (e.g. data volume for data downlink capabilities, and larger overheads due to telescope slew & settle). If you need to explore shorter exposure times than what is available in RIST, you can still use the Pandeia engine to explore the MA table truncation options, but caution is needed when considering the truncation.

    • More information about the MA tables can be found on the WFI MultiAccum Tables RDox page.

  • RIST uses the following abbreviations:

    • IM: Imaging mode

    • HLWAS: High Latitude Wide Area Survey

    • HLTDS: High Latitude Time Domain Survey

    • GBTDS: Galactic Bulge Time Domain Survey

  • The computed SNR values can be visualized by hovering the cursor over the points in the plot.

  • Pandeia cannot calculate a SNR for saturated sources. In RIST, saturated points are set to zero and marked as triangles in the plot.

  • The x-axis shows the central wavelength of each Roman filter.

  • Once you are satisfied with the estimated SNRs, you should use the Roman WFI ETC to provide specific observing parameters for Roman APT. Documentation on the Roman WFI ETC can be found here.

Caveats#

  • Any limitations that Pandeia bears are also interited by RIST. Please see RDox for Pandeia for the details on caveats for using Pandeia for Roman.

  • The current version does not handle the following features and the users need to use Pandeia for:

    • Extended sources – all SNR computations are performed for a point source.

    • The spectroscopic observing mode – future versions of RIST will support the WFI spectrocopic mode.

    • Truncation of the MA tables.

Additional Resources#

Software release#

We expect to release an updated version of RIST pre-computed grid every time Pandeia updates its reference files for Roman. The current grid is generated using the following versions of Pandeia and its reference data:

  • Pandeia Engine version: 2026.1

  • Pandeia Refdata version: 2026.1

  • Pandeia PSF version: 2026.1

Help#

For assistance with RIST, please contact the Roman SOC Help Desk.

About this Notebook#

Author: Eunkyu Han
Last Updated: 2026 January

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