Groups & Integrations Tool

In planning JWST exoplanet observations, ExoCTK's Groups & Integrations Tool provides a framework for estimating the number of groups and integrations for a given transiting exoplanet exposure.

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      See also: Understanding Exposure TimesJWST Exposure Time Calculator OverviewJWST Data Rate and Data Volume Limits

ExoCTK's Groups & Integrations Tool is a JWST observation planning tool for transiting exoplanet observations that calculates the optimal number of groups and integrations. Given some information about the target star, transit characteristics, and the planned instrument settings (i.e., subarray, and filter configuration), the tool uses a pre-calculated set of groups for a range of magnitudes and stellar spectral types (using Pandeia, which powers the JWST ETC) to interpolate the saturation limits for this input information, which allows the tool to calculate the optimal number of groups and integrations (that maximize observing efficiency without saturation) for use in observation planning. 

The Groups & Integrations Tool is designed to be a quick-look tool to determine the optimal number of groups and integrations for a given transiting exoplanet observation. Currently, this tool is likely to overestimate saturation in comparison to the ETC; it may predict fewer groups and put users in less danger of over-saturating their observation.

This tool does not check for possible caps on the maximum number of groups and integrations due to limits on the data that can be stored onboard JWST. Therefore, before submitting their proposals, it is imperative that users always double-check their calculations against results from the official JWST ETC and, more importantly, in APT, in order to confirm consistent results between the tools. The JWST ETC and APT always take precedence over the results of ExoCTK's Groups & Integrations Tool.

The Groups & Integrations Tool can be used via a web form, as described below.



Using the web interface

Users may navigate to the Groups & Integrations Tool by clicking on the Groups and Integrations button under the Observation Planning section on the ExoCTK homepage, as shown in Figure 1. Or by going directly to the tool's webpage.

Figure 1. Groups & Integrations on ExoCTK's homepage

To start a calculation, the following inputs are needed:

  • The optional Target Name field (e.g., "WASP-18 b"); if used, clicking the Resolve Target button will reload the page with Stellar Parameters fields automatically filled out. These parameters are retrieved from Exo.MAST, as shown in Figure 2.
  • If no target is specified, provide values for the two Stellar Parameters fields; enter the K-band Vega magnitude of the target star and select an appropriate Phoenix stellar atmosphere model for the target star from the drop-down list.
  • The length of the observation, Observation Time, either in units of hours or days. 
  • Parameters that define the exposure, as shown in Figure 3. These are the number of Groups per Integration (to optimize this number, enter 0), the Instrument, as well as science and target acquisition Filters and Subarrays.
  • A Maximum Saturation level for the given instrument configuration. Saturation can be specified as counts or full well percentage. Then, enter the appropriate amount in The level of saturation field, as shown in Figure 4. As with PandExo, the presented saturation levels are signal limits and not actual full well depths of the detectors (for more details on this terminology, see the TSO Saturation article).

Figure 2. Groups & Integrations target input interface

Figure 3. Groups & Integrations Inputs

Figure 4. Defining Maximum Saturation

Once all of the fields described above are filled out appropriately, click the green Calculate Groups and Integrations button to get your results.



Understanding the Groups & Integrations Tool output tables

Once the calculation is complete, you will be redirected to a results page, with a layout similar to the one shown in Figure 5. The results page has 5 output tables. The first table, called "Source Specifics," (not shown in Figure 5) contains the stellar properties and transit observation time values used for the calculation, entered earlier the web form.

The following 4 tables are split between two sections: "Target Acquisition" and "Science Observation," containing information about the target acquisition and the science observation. In each of their subsections, the first table shows the input and instrument parameters and the second table shows some ready-to-be-ingested APT information.

For "Target Acquisition," the second table shows the results for the minimum and maximum number of groups so the user can select the one that best accommodates their observations.

For the second table under "Science Observation," if Groups per Integration was set to 0, the table shows optimal values to maximize observational efficiency; otherwise, it shows results for the Groups per Integration value provided by the user.

Figure 5. Groups & Integrations output example



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