Phase Constraint Calculator Tool
The Phase Constraint Calculator provides phase-constraint observation windows for exoplanet transits and eclipses for use in the Astronomers Proposal Tool (APT).
Scheduling start times for visits targeting periodic events such as exoplanetary transits and eclipses with JWST typically requires one to define a range of times—through a window in phase-space — that the observatory should aim to target. Due to uncertainties on the exact scheduling time of JWST observations, these windows are strongly encouraged to be of one hour or larger in order to not incur direct scheduling overheads. The Phase Constraint Calculator provides a simple interface for calculating possible JWST observation windows for direct input to APT.
The web-based version of this tool is part of the STScI's Exoplanet Characterization ToolKit (ExoCTK) suite of web-based services. The tool is also available as an importable python module through the ExoCTK python library.
Using the web interface
The web-based interface for the Phase Constraint Calculator has several options to retrieve phase constraints for a given system. First, orbital data (such as the Period, Eccentricity, Argument of periastron and Inclination) can be ingested directly by the user or chosen to be retrieved directly from exo.MAST by entering the exoplanet name in the Target Name box, and clicking the Resolve Target button; an example for WASP-18b is shown in Figure 1. In addition, the user has to decide if phase constraints are to be calculated for Primary Transit (i.e., when the planet passes in front of the star from our point of view at Earth/JWST) or Secondary Eclipses (i.e., when the planet passes behind of the star). The example in Figure 1 shows the default case which is PrimaryTransit.
Once the data have been input, the user can hit the green Calculate Phase Constraint button to perform the calculation, as has been done in the example below:
Using the Phase Constraint Calculator output parameters in APT
Once results have been obtained with the Phase Constraint Calculator tool, they can be placed in the APT proposal. To do this, go to the APT Observation Folder, select the Observation, and click Special Requirements. Here, under Add, select Timing → Phase, which will in turn open the Phase window where you will be able to enter the results from the calculator. The example in Figure 4 shows how results obtained above for the Primary Transit of WASP-18b were entered in the APT Phase fields.