JWST Interactive Sensitivity Tool

The JWST Interactive Sensitivity Tool (JIST) is a quick-look tool to explore the observation feasibility for basic JWST observing modes. JIST allows you to explore signal-to-noise values in real time by adjusting source flux density or telescope exposure time.

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JIST uses a pre-computed grid of simple point source calculations made with the ETC engine (Pandeia) and interpolates within that grid to provide you with insight into the S/N you can obtain for potential JWST integrations. JIST is designed using the Bokeh Python plot functionality to provide a flexible, interactive environment.

JIST runs directly in your browser window, at this website: jist.stsci.edu

By design, JIST offers less flexibility than the JWST ETC in exchange for faster operation. As such, there are a number of factors you should be aware of when using JIST:

  • JIST offers a flat spectrum point source target. Hence, the JWST ETC will be more accurate for different source spectral shapes or for extended sources.
  • JIST offers a single background option of 1.2 times the minimum zodiacal background. A higher fidelity treatment of background and more options are available in the JWST ETC.
  • JIST offers a single integration, which in turn gives it a maximum exposure time.
    • For observations with multiple integrations, the expected S/N can be scaled as the square root on Nint.
    • If you increase the flux density enough to cause saturation, the affected points are removed from the display. This is because JIST can no longer calculate a relevant signal-to noise-ratio.

After exploring the possibilities with JIST, you should use the JWST ETC to determine the specific exposure specifications you will need for entry into APT.

JIST interface

Figure 1. The JIST GUI

This is a screenshot of the GUI interface you will see when you open JIST. By selecting an observing instrument/mode on the left, the plot will change as needed for that mode. As you move the sliders, results in the plot will adjust accordingly.
The main JIST interface is shown in Figure 1. It consists of a flux density slider, an exposure time slider, a group of mode selection radio buttons, and the Bokeh plot itself. The interactable parts of the plot are:

  • Sliders: the source brightness and exposure time sliders allow you to adjust the assumed flux density or AB magnitude of the point source, and the integration time on the detector (note that all Bokeh plots are for a single integration). The range of the sliders varies depending on the mode chosen.
  • Mode selection buttons: these allow you to choose the instrument and observing mode. The wavelength range on the plot changes automatically as different modes are selected.
  • Bokeh widgets, described from top to bottom.
    • Bokeh website widget (): This opens a link to the Bokeh website.
    • Pan control (): This allows you to pan the plot (without changing its scale).
    • Box zoom (): This allows you to zoom in on a particular part of the plot (by drawing a box on the plot). The box you draw will zoom in to occupy the entire plot.
    • Reset (): This allows you to reset the plot to its original range and scale.
    • Save (): This allows you to save the current plot as an image file.
    • Crosshair (): This toggles a crosshair on and off over the plot. It is on by default.
    • Hover tool (): This toggles on or off whether the plot should show annotations (e.g., grating/filter information) when you hover the cursor over a data point. It is on by default.
  • Legend: This shows the currently displayed modes. For spectroscopic data, clicking on a legend entry will hide the corresponding mode from the plot.

Units conversion

JIST allows users to specify inputs as flux density (in mJy) or as AB magnitudes. If you need to convert your source information, there is a handy conversion tool available.

Moving from JIST to the JWST ETC

JIST is an exploratory tool for basic checking of feasibility. Once you have used JIST to determine the feasibility of your observation, you can move on to using the online JWST ETC tool to continue planning your observations. In many cases, it will be possible to improve signal-to-noise ratios by fine-tuning exposure parameters and observing strategies in the ETC. 

Words in bold italics are also buttons 
or parameters in GUI tools. Bold 
style represents GUI menus/
panels & data software packages.

After obtaining an overview of the ETC and its functionality, you can go directly to the ETC Quick Start mode (via the green button at the top left of the webpage) to start using the ETC. Once you are comfortable, actually sign in to the ETC so you can save your work.

Use the main JDox navigation menu to access any of a number of topical articles covering various aspects of the JWST ETC. Also, there are a number of ETC video help tutorials available to help get you started.

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