Step-by-Step APT Guide for NIRCam Time-Series Imaging Science Use Case

Instructions are provided for filling out the APT observing template for the JWST NIRCam Time Series Imaging Observations of HAT-P-18 Science Use Case.

Completing the APT template

Reference: NIRCam Time-Series APT TemplateAPT Workflow Articles

We now construct an APT file that will execute our desired observations. Completing the APT proposal requires the following steps:

  • Entering the proposal top-level information: Title, abstract, PI and co-PI names, proposal category
  • Target definition
  • Observations
  • Special Requirements
  • Target Acquisition
  • Visit Planner
  • Smart Accounting
  • Submission

The steps highlighted in bold will be covered in this step by step guide for the HAT-P-18 example science case. The other steps are generic to every proposal, and we refer to the above reference articles for further instructions.

Configuring the observations

The rationale for the observation settings and choices were discussed for this case in the main article for this science case, and in the accompanying step by step ETC guide. 

In the Observations panel, we click on "New Observation Folder", and enter a name and short description for our observation in the top-level information panel that is created. 

In the Observations table, we select Instrument: NIRCam and Template: NIRCam Time Series, and enter a Label if wanted; then select the Edit.... button to continue to the detailed definition of the observation. 

In the Observation detail page, we enter the following information:

  • select HAT-P-18 as target (this should be defined beforehand in the Targets section)
  • Time Series Parameters section:
    • select the SUB64P subarray
    • set Exp/Dithers to 1; time series observations are best executed in a single exposure for optimal stability.
    • select the Pupil/Filter combination CLEAR/F210M for the Short Wavelength channel
    • select the Pupil/Filter combination CLEAR/F444W for the Long Wavelength channel
    • choose the RAPID readout pattern
    • set NGROUPS = 10 according to our ETC calculations
    • set NINTS = 60,000

60,000 integrations gives a total integration time of ~9.3 hours, which covers 3 × T14 (2.71 hours), plus 1 hour for detector settling. 

Special Requirements

In the Special Requirements section we  first select the Time Series Observation and No-Parallel options. The No-Parallel requirement should always accompany the TSO requirement. 

We also specify here the phase constraints for the transit observation, to ensure the observation is scheduled at the correct time. For this we use the Phase requirement, listed under Timing. In the phase constraints box that appears, we enter:

  • Phase = 0.43854 to 0.43927,
  • Period = 5.508023 days
  • Zero-Phase = 2454715.02174 HJD.

These parameters are obtained from the literature. For HAT-P-18b, Hartman et al. (2011), predict that the secondary eclipse will come 2.63 days after transit, at an equivalent 0 eccentricity PHASE of 0.4772, given its 5.508 days period. We will center the schedule of the exposure to start 5.07 hours before the predicted secondary eclipse time, allowing for 1 hour of detector settling and one transit time before the predicted time of the secondary eclipse start. This corresponds to PHASE 0.4385 and will allow us to catch the secondary eclipse if it occurs within ±1 transit time (2.71 hours) of the predicted value. We thus set the special requirement to start the exposure at PHASE 0.4385 to 0.4392 with period 5.508023 days and zero-phase 2454715.02174 HJD, just outside of the minimum allowed 5 minute tolerance.

Target Acquisition

We determined that we can use the science target for TA, so we select in the Target ACQ drop-down list "Same Target as Observation". In Acq Exposure Time, we select the RAPID readout pattern, and NGROUPS of 17 from the list of options. This was informed by our ETC calculations in the Step by Step ETC guide for this example science case. 


The total program length is 12.69 hours, including 8.36 hours of science time.

Figure 1. APT observation setup

Screenshot of APT NIRCam time-series template with this program's selected observation parameters.

The APT file for this program can be downloaded here: NIRCam_imaging_time_series_example.aptx



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