The Roman Interactive Sensitivity Tool (RIST)

The Roman Interactive Sensitivity Tool (RIST)#

Kernel Information and Read-Only Status#

To run this notebook, please select the “Roman Research Nexus” kernel at the top right of your window.

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#

The 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 Pandeia (the Exposure Time Calculator) – 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 number of resultants, while using a single on-axis point source with a default background of Pandeia. For the details of the background, see Notes below.

Requirements#

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

Import#

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

If running within VS Code, Jupyter Notebook, or JupyterLab, set the WebSocket to conect to Bokeh before importing plot_rist.

# Set up Bokeh
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 *

Now, 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.

  • All calculations were done for Detector 1 (SCA01). More information on the detectors can be found here.

  • The background was calculated using the JWST Backgrounds Tool.

    • The “minzodi” background option refers to a background at RA = 17:26:49 & Dec = -73:20:03 (J2000). At this location, the zodiacal emission is 20% higher than the celestial minimum.

    • The “benchmark” background refers to the background at the minzodi location on June 19, 2020.

  • Multi-accumulation (MA) tables describe the sequence of individual reads that are combined into resultants and that comprise the up-the-ramp sampling during a single exposure of the WFI detectors. The MA tables currently available in RIST are based on the RST-WFI-DESC-0110 Revision E, and are thoroughly documented on RDox.

  • RIST uses the following abbreviations:

    • IMG: Imaging mode

    • HLWAS: High Latitude Wide Area 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 satisfied with the estimated SNRs, use the Roman WFI ETC to further plan your WFI observations. Documentation on the Roman WFI ETC is available here.

Caveats#

  • Any limitations of Pandeia are also inherited by RIST. For details on the caveats of using Pandeia for Roman, please refer to the RDox for Pandeia.

  • 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.

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_version: 2024.12

  • Pandeia_refdata: 2024.12

Help#

For assistance with RIST, please contact the Roman SOC Help Desk through https://stsci.service-now.com/roman

About this Notebook#

Author: Eunkyu Han
Last Updated: 2025-01-08

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