JWST Exoplanet Observations Proposal Tools

The Exoplanet Characterization Toolkit (ExoCTK) is a suite of web tools and a Python library created to help observers plan exoplanet observations for the James Webb Space Telescope (JWST). 

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See also: JWST General Target Visibility Tool Help, JWST Moving Target Visibility Tool Help, and JWST Coronagraphic Visibility Tool Help.

The ExoCTK suite of tools were developed to meet the unique requirements for planning JWST exoplanet observations (with features not available in the more generalized General Target Visibility Tool (GTVT) and JWST Exposure Time Calculator). This suite can be run via a web interface or by downloading the Python version to run on a local machine. 

In planning observations of transiting exoplanets, estimating the precision needed to detect a given feature can be challenging. Also, the process of scheduling the observation could be difficult. ExoCTK simplifies this process for observers; summaries of available tools are listed below to aid users in discovering which tools will best suit their needs. 

Contamination Overlap tool

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

There are 2 calculators in the Contamination Overlap tool: the Visibility Calculator (Calculate Visibility button) and the Contamination Calculator (Calculate Visibility and Contamination button). Used together, these calculators help users determine the best position angles for minimizing potential contamination in their observations. 

The Visibility Calculator determines the position angles (PAs) for when your target is visible and its observing windows. On the ExoCTK website, the Visibility Calculator produces an interactive Bokeh plot with aperture position angle (APA) as a function of time; users also have the option to download a CSV file of the data in table format. The Visibility Calculator is available for all JWST instruments.

The Contamination Calculator determines the degree of spectral contamination that lands on the target at every APA. It is available online for the NIRISS single object slitless spectroscopy mode.

Further information is available in the ExoCTK Contamination Overlap Tool article.

Forward Modeling tool 

An important component in creating a JWST proposal for exoplanet transits involves having exoplanet atmospheric models available to help in predicting what JWST might be able to observe. The Atmospheric Forward Modeling tools (with Fortney Grid and Generic Grid options) of ExoCTK provide a simple interface for retrieving atmospheric models from the grids of Fortney et al. (2010) (as used in Sing et al. 2016) and Goyal et al. (2018) that are useful for proposal preparation.

Further information about the results of these tools and their differences can be found in the Forward Modeling Tool article. 

Groups & Integrations tool

Another aspect of creating a JWST observation of a transiting exoplanet is providing the optimal number of groups and integrations. ExoCTK provides an interactive online tool, the Groups and Integrations Calculator, where the user can provide some information about the background star, the transit characteristics, and the planned use of JWST (i.e., the instrument, subarray, and filter configuration) to find these optimal numbers for observation. This tool interpolates the planned transit observation to the nearest information from Pandeia (which powers the JWST ETC) and calculates the optimal number of groups and integrations to use in observation planning.

Further information is available in the Groups & Integrations Tool article.

Limb Darkening Calculator

The shape of transit light curves, observed or simulated, depends on how stellar intensity varies along the exoplanet transit chord. The ExoCTK Limb Darkening Calculator returns the limb-darkening coefficients that describe the center-to-limb variation of stellar intensity for a specified wavelength interval. 

Further information is available in the ExoCTK Limb Darkening Calculator Tool article.

PandExo, the Exoplanet Exposure Time Calculator (ETC) 

To fully prepare a JWST proposal, a user will need to determine the optimal instruments needed, and calculate the best exposure parameters, to successfully perform detections of their sought after atmospheric features. PandExo, the Exoplanet Exposure Time Calculator, provides a simple framework for performing these calculations, helping users to optimize their observations for transiting exoplanet.

Further information is available on the ExoCTK Exoplanet ETC, PandExo article.

Phase Constraint Calculator tool 

Users writing JWST proposals using the Astronomers Proposal Tool (APT) must provide observation windows for their targets. These windows for periodic phenomena have to be defined through phase constraints. The Phase Constraint Calculator provides a simple online interface for calculating these windows for both exoplanet transits and eclipses. 

Further information is available on the ExoCTK Phase Constraint Calculator Toolarticle.


Fortney, J. J., et al. 2010, ApJ, 709, 2, 1396
Transmission Spectra of Three-Dimensional Hot Jupiter Model Atmospheres

Goyal, J. M., et al. 2018, MNRAS, 474, 4, 5158
A library of ATMO forward model transmission spectra for hot Jupiter exoplanets

Sing, D., et al. 2016, Nature, 529, 7584, 59
A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion

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