Enter proposed Targets

See also: APT Targets

Target information is entered by selecting Targets in the tree editor, which provides options in the active GUI window. In this case, choose the Fixed Target Resolver button and enter WASP-39b in the Object Name search box of the pop-up window. By clicking Select Object as Target, the target name and coordinates are imported to the APT observation template. 

This target was selected in the left-hand tree editor to enable us to provide additional information in the target GUI. In both the Name in the Proposal and Name for the Archive fields, update the name of the object to the more familiar WASP-39b. In the Category drop-down menu, select Star. In the Description menu, select Exoplanets. The proper motion of the source is, in this case, automatically extracted from SIMBAD.

Observations

See also: APT Observations

Selecting Observations in the tree editor, click on the New Observation Folder, and in the Label field, enter WASP-39b NIRISS SOSS.

Next, click Observation 1 in the tree editor to open the observation template in the active GUI window. In the Instrument pull-down menu, select NIRISS, and then select the NIRISS Single-Object Slitless Spectroscopy template in the Template pull-down menu. Note that only parameters of interest to NIRISS SOSS are shown in the GUI. In the Target pull-down menu, select WASP-39b which was defined above.

Complete APT observation template for NIRISS SOSS

See also: NIRISS SOSS APT Template

Target acquisition

A target acquisition (TA) is required when using a subarray with SOSS to ensure the target is placed on the "sweet spot" on the detector. As described in the step-by-step ETC guide, a SNR ≥ 30 is required to ensure the TA will succeed, otherwise the observation fails.

For this science program, a TA is performed on the target, so the acquisition target in the Target ACQ pull-down menu is kept at its default value of SAME TARGET AS OBSERVATION.

Using the results from the ETC calculations, select SOSSFAINT for Acq Mode, NISRAPID for Acq Readout Pattern, and 19 Acq Groups/Int. For your own tracking purposes, it is recommended you include the ETC workbook and calculation ID number in the Acq ETC Wkbk Calc ID field so the TA SNR calculations can be verified by instrument scientists during technical reviews after the proposal is accepted.  In this example, do not include an ETC workbook ID number in the provided APT file since a unique ID number is generated when an example workbook is added to a user's list of workbooks.

SOSS parameters

Populate the SOSS parameters portion of the SOSS observation template with the exposure parameters determined from the step-by-step ETC guide. Select SUBSTRIP256 from the Subarray pull-down menu. The only permitted Readout Pattern when using a subarray in the SOSS observing mode is NISRAPID, and is the only option thus available in the APT template. Also from the step-by-step ETC guide article, it was calculated that 8 Groups/Int and 535 Integrations/Exp was needed for this observing program.

The yellow exclamation point indicates a warning for this exposure, which alerts the user that, due to the long exposure (> 10,000 s), a high gain antenna move may be performed during the exposure which can induce jitter that affects the science observation. This is an informational warning, and no action is required.

An optional exposure with the F277W filter is also taken to help in modeling the contamination between the overlapping 1st and 2nd order, and to isolate potential 0th order sources. To do so, select the box to Include Short First Exposure and F277W exposure. Similar to the main science exposure, the only permitted Readout Pattern is NISRAPID. From the Step-by-Step ETC guide calculation, 8 Groups/Int and 10 Integrations/Exp were needed.

Define Special Requirements

See also: APT Special Requirements

To observe the transit of the exoplanet, phase constraints need to be applied to the proposal, which are specified in the Special Requirements tab of the observation template. Two special requirements were already added by APT: Time Series Observation, which signals the pipeline how to process the data and causes APT to give a warning rather than an error about the exposure duration exceeding 10,000 s, and No Parallel Attachments, which prohibits a parallel observation from being scheduled simultaneously with this program.

In the Special Requirements dialog, click Add to specify the phase special requirement for this observation. The phase range of the transit needs to be specified, where APT accepts values from -1 to 1. By convention, the transit occurs at phase = 0.0. The phase is specified relative to the period of WASP-39 (P_WASP39), which is 4.055259 days.

To compute the phase-constraints, use the ExoCTK Phase Constraint tool. By querying the properties of WASP-39, you will find that the phase-range to target the primary transit of WASP-39b is from 0.9532171270277271 to 0.96349185095206. According to the results, the transit center is at 2456401.39763—this is entered as the Zero phase (HJD) and the period of the orbit is 4.055259 days, which is entered as Period in APT.

Run Visit Planner

See also: APT Visit Planner

The APT Visit Planner tool checks the schedulability of an observation and whether guide stars can be found to support the observation. To check the schedulability of this observation as specified, make sure the observation was selected in the tree editor and clicked on the Visit Planner icon in the top tool bar. Then, select Update Display in the resulting active GUI window. After a few moments, the Visit Planner returns with a confirmation that the observation is schedulable (green check on the selected observation).

Because JWST has time-variable observational constraints—related to the position of the sun relative to the observatory's orbit—each target's RA and Dec has a specific set of ranges of days that targets can be observed.  You can "zoom in" on one of those ranges: using the zoom slider bar above the figure and manually adjusting the grey box to the right of that slider bar, you can isolate a the leftmost range of observing windows. By zooming in on specific windows, you can see the specific calendar dates when this target can be observed by JWST, given the phase constraint. It is good practice to confirm future dates of an estimated transit opportunity.

Run Smart Accounting

See also: APT Smart Accounting

To minimize excessive overheads, run Smart Accounting from the Visit Planner page by selecting the Run Smart Accounting option. The charged time for the observing program, including exposure time and overheads, is now accurately calculated.