Step-by-step APT observation instructions for the NIRSpec BOTS Prism multistripe observations of WASP-62b are presented and discussed in this example science program.

See also: NIRSpec Bright Object Time-Series Spectroscopy, NIRSpec Bright Object Time-Series APT Template, JWST APT Video Tutorials

The Astronomer's Proposal Tool (APT) is used for submitting JWST proposals. There are multiple components to an APT submission: generic proposal information, target information, and exposure specifications for the proposed program. This article discusses how to fill out the APT observing template for the example science program. 

Fill out proposal information

See also: JWST Astronomers Proposal Tool Overview

Enter proposed targets

See also: APT Targets, Fixed 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 New Fixed Target option and enter WASP-62b in the Name in Proposal and Name for the Archive boxes. Enter the coordinates and proper motion from the Gaia Archive: RA = 05 48 33.5933 and Dec = -63 59 18.39 and proper motion RA = -15.439000000000002 and proper motion Dec = 26.151 mas/yr. The Epoch is 2000. In the Category drop-down menu select Star, and in the Description menu select Exoplanets and F stars.

Create another target to enter information for the offset source to be used for target acquisition. Using New Fixed Target, enter WASP-62_TA (the selected TA target is Gaia DR3 4756652365943137920) in the Name in Proposal and Name for the Archive boxes. Enter the coordinates, proper motion, and parallax from the Gaia archive: RA = 05 48 28.889, Dec = -63 58 57.216, proper motion RA = 1.78 mas/yr, proper motion Dec = 0.66 mas/yr, and parallax = 0.003 arcsec. The Epoch is 2016. In the Category drop-down menu, select Star. In the Description menu, select K stars.

Observations

See also: APT Observations

Selecting Observations in the tree editor, click on the New Observation Folder, and in the Label field, enter WASP-62b BOTS Prism Multistripe.

Next, click "Observation 1" in the tree editor to open the observation template in the active GUI window. Enter "WASP-62b - Prism Multistripe" in the Label field. In the Instrument pull-down menu, select NIRSpec, and then select the NIRSpec Bright Object Time Series template in the Template pull-down menu. Note that only parameters of interest to NIRSpec BOTS are shown in the GUI. In the Target pull-down menu, select WASP-62b, which was defined above.

Complete APT observation template for NIRSpec BOTS

See also: NIRSpec Bright Object Time-Series APT Template

Target acquisition parameters

Fill out the target acquisition (TA) parameters following the findings on signal to noise from the ETC calculation: TA option is WATA (wide aperture TA). The target for TA is WASP-62_TA, which was defined above. Thus, select WASP-62_TA in the Acq Target pull-down menu. Select the SUB32 subarray and the CLEAR filter, and the NRSRAPID readout, consistent with parameters found in the ETC TA sensitivity calculation for this offset star. With the NRSRAPID readout pattern, the exposure time will be 0.08 s for the TA, as listed in the ETC Detector Setup pane when the Subarray and Readout pattern are selected. 

Science parameters

Populate the science parameters portion of the observation template based on the exposure parameters determined from the step-by-step ETC guide. Given the different definitions of Total Exposure Time between the ETC and APT, you will need to do some additional calculations to determine the number of Integrations/Exp and the number of Exposures/Dith to specify in APT. 

For WASP-62b, you will need to choose the SUB64M8_PRISM subarray and the PRISM/CLEAR grating/filter option. From the step-by-step ETC guide, the exposure time for 1 Integrations/Exp is 1.09 s with this subarray and grating/filter selection. To cover the ~9.38 hr observation window based on the exposure times defined in ETC, you would need 30,810 Integrations/Exp. Since exposure times are defined differently in APT, you need to multiply 30,810 by the number of stripes in your chosen BOTS Prism multistripe subarray (30,810 Integrations/Exp × 8 stripes = 246,480). Since 246,480 exceeds the APT integration limit of 65,535, you will need to increase the number of Exposures/Dith to ensure that the time-series observation stays within this integration limit. To determine the number of Exposures/Dith, divide 246,480 by the APT frame limit (65,535) and round up to the nearest whole number (246,480 / 65,535 = 3.7 = ~4). The number of Integrations/Exp will then be 246,480 / 4 = 61,620. In APT, specify 4 Exposures/Dith, select the NRSRAPID readout pattern, and choose 3 Groups/Int with 61,620 Integrations/Exp to cover the transit window plus the padding time before and after the transit, which gives a Total Exposure Time of 33,679 s (9.36 hrs).

The observation described here requests an exposure time of 33,679 s, and it is likely that the HGA will re-point during the course of the exposure time. The HGA repoints last approximately 60 s, and the source position and thus the position of the spectra will slightly change during the HGA movement, resulting in short excursions in the flux in the science spectra. The integrations affected by HGA re-points can be removed from the measured time series during data processing and analysis.

Define special requirements

Timing special requirement

The timing special requirements are needed to define when the transit observation of WASP-62b should start. The phase range of the transit needs to be specified, where APT accepts values from 0 to 1. By convention, the transit occurs at phase = 0.0. The phase is specified relative to the period which for WASP-62b is 4.41195 days, or 105.8868 hours (P_W62). 

To cover the transit window, define a start time of t_start = T₁₄ + 0.75 hours (where T₁₄ is the transit duration of 3.816 hours¹) to be consistent with T_dwell which was defined for the total exposure time. Thus, t_start = 4.566 hours. The starting phase is then p_start = 1 - (t_start + 1 hour)/P_W62 and the ending phase is p_end =  1 - t_start/P_W62. The phase range for WASP-62b is thus 0.9474 and 0.9569.

To add these values, click Add in the Special Requirements tab and select Timing → Phase. Enter 0.9474 and 0.9569 into the Phase range, 4.41195 for the Period (with Days as the units), and set Zero phase (HJD) to 2458850.59934, the center time of the primary transit. (Note that any transit following the initial one defined by the phase special requirement could also be selected for the execution window.) 

Time-series observation special requirement

The NIRSpec BOTS mode observation will automatically have a Time Series Observation Special Requirement added. This shows up as an implicit special requirement for all NIRSpec BOTS mode observations in APT. The purpose of this special requirement is to ensure that the NIRSpec BOTS data gets processed through a particular pipeline calibration workflow specific for time-series exposures. Users do not need to add this special requirement, but it is useful to take note that it is automatically set.

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.