APT Instructions for MIRI and NIRSpec SN 1987A Observations

The JWST Astronomer's Planning Tool allows observers to design NIRSpec Integral Field Unit observations. In this article we show the step-by-step instructions to design the observations following a real science case, namely IR imaging and spectroscopy IFU observations of Supernova 1987A.

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In this article we describe the steps that are needed to create an APT document taking into account observations made with three JWST instruments: MIRI and NIRSpec IFU as primary instruments and NIRCam as a parallel. The process includes the creation of a new proposal, the definition of targets, and the design of the observations: MIRI imagingMIRI IFUMIRI IFU Background, and NIRSpec IFU.



Creating a new proposal

From the main APT Navigation Tree, select File → New → New JWST proposal.

 Under the "Proposal Information" tab fill out the following information:

  1. Title
  2. Abstract
  3. Category
  4. Cycle
  5. Scientific Category
  6. Science Keywords
  7. Attach PDF of science justification
  8. Fill out Proposal Description tab
  9. Add PI and CoI information

Figure 1 shows a screen grab of these parameters. 

Figure 1. Creating a new JWST proposal


Create the Fixed Targets 

Under the "Targets" tab it is possible to add three fixed targets: 

  1. Add a fixed target. This needs to be done twice: first for the MIRI imager (SN-1987A)  and next for the MIRI/IFU (SN1987A-MRS) because a dedicated background observation will only be created for the IFU.
  2. Add a fixed target (SN1987A-BKG) for the background coordinates.
  3. For the MRS target, select “Observations of this target require companion background observation(s)” and select the background target under "Target Selection".

Figure 2 shows a screen grab of these parameters. 

Figure 2.

One of the three targets pane is shown here. This view corresponds to the main source of interest SN-1987A. Three target tabs are shown in the APT navigation tree.


Observations Folder

Under the "Observations" tab four observations are created, one for each set of instruments/observing modes/configurations; i.e.,  MIRI Imaging, MIRI IFU, MIRI IFU background, and NIRSpec IFU.

MIRI Imaging

In this observation we perform imaging with 4 MIRI bands using the BRIGHT SKY SUB array with the JWST imaging instrument NIRCam in parallel.  The NIRCam parallel observation uses all of its  wide filters and one medium filter. The medium filter is to be determined depending on the science case. Set the following parameters in APT:

  1. Prime Instrument: MIRI
  2. Select the Template as  'MIRI Imaging'
  3. Coordinated Parallel: Select 'MIRI-NIRCam Imaging'. Note that when the field  'Coordinated Parallel' is activated, the 'NIRCam Imaging' pane appears at the bottom of the APT interface.
  4. Target: SN-1987A
  5. Subarray: BRIGHTSKY
  6. Dithers: add a dither pattern for each filter. In this case a '9-POINT-MIRI-F770W-WITH-NIRCam' will do.
  7. Filters: Add all filters with corresponding exposure parameters (Groups per integrations, Integration per Exposure), readout mode (FAST), and dither pattern that was selected in the previous step. The exposure times are automatically calculated by the APT. Discussion on the ETC use case page describes the estimated S/N in the data based on the selected exposure parameters. 
  8. Repeat this procedure under the NIRCam Imaging tab. Select the NIRCam filters for both Long and Short Wavelength Channels as shown in Figure 3. 

Figure 3 shows a screen grab of these parameters. 

Figure 3. MIRI imaging with NIRCam as a parallel

[Top Panel] MIRI imaging parameters. [Bottom Panel] NIRCam imaging parameters when used as a parallel observation.

MIRI IFU

The focus of this observation is to obtain spectra of the ejecta from 1987A using MIRI. This involves observations of both the science target (described here), and the MIRI MRS background observation (described below).   Create the science observation by using the following parameters:

  1. Instrument: MIRI 

  2. Template: MIRI Medium Resolution Spectroscopy 

  3. Target: SN 1987A-MRS 

  4. Fill out Target Acquisition Parameters using the same target and filter F1000W.

  5. Dithers: Add 4-Point dither pattern for the MRS.

  6. Set  'Simultaneous Imaging' to YES.

  7. Set 'Imager Subarray' to BRIGHTSKY 

  8. Wavelength: the Short/Medium/Long spectral settings were split off into separate observations in order to be able to use multiple filters for the simultaneous imaging.

  9. Specify exposure parameters for simultaneous imaging and the short and long MRS channels.  Discussion on the ETC use case page describes the estimated S/N in the data based on the selected exposure parameters. 

Figure 4 shows a screen grab of the parameters used for the MRS Short spectral setting. 

Figure 4. MIRI IFU observation

The MIRI IFU observation. The Short, Medium, and Long spectral settings were split off into separate observations in order to be able to use multiple filters for the simultaneous imaging.

MIRI IFU background

The focus of this observation is to obtain spectra of the ejecta from 1987A using MIRI.

  1. Create the background observations by duplicating the MIRI IFU observation folder.
  2. Change the target to SN1987A-BKG.
  3. Under the "Special Requirements" tab, link the MRS IFU and MRS IFU background observations to be executed in a non-interruptible sequence, as shown in Figure 5.

Figure 5. MIRI IFU observation

Top panel: The MIRI background observation was also split into Short, Medium, and Long gratings.
Bottom Panel: This view shows the Special Requirements used to link the MRS IFU and MRS IFU background observations.

NIRSpec IFU 

The article NIRSpec IFU Template APT Guide provides a thorough description on how to fill out each parameter. 

  1. Select NIRSPEC as instrument 
  2. From the available templates, select 'NIRSpec IFU Spectroscopy'.
  3. Select the Target as SN-1987A
  4. Leave the Target Acquisition method as TACQ, which corresponds to Standard Acquisition. (TACQ parameters do not need to be defined in proposals).
  5. In the Science Parameters section, select a 4-POINT dither pattern
  6. Three filters are used combined with their corresponding medium resolution gratings.  Exposure parameters are set for NGroups and Nints and the exposure time is automatically calculated by APT. Discussion on the ETC use case page describes the estimated S/N in the data based on the selected exposure parameters. 
  7. Duplicate the observations for each grating/filer combination with Leakcal selected (these are taken with the IFU aperture closed in order to obtain the pattern of leakage from the open (failed) microshutter arrays

Figure 6. NIRSpec IFU observation

The NIRSpec IFU observation template as used to plan the observation of SN-1987A.


View apertures in Aladin

The supported viewer of APT is Aladin. By clicking the 'View in Aladin' button at the top of the APT interface, it is possible to display the apertures associated to each planned observation. Figure 7 shows the example NIRSpec IFU observation with two dither pointings. 

Figure 7. Aladin view

The NIRSpec IFU field of view plotted using the Aladin viewer option. The background image is an HST/WFC3/UVIS drizzle product generated using images obtained with filter F625W.


APT File

The APT file containing the observations described above can be found in the link below. 

Example APT file. This is the APT file used to demonstrate the complete example in this article.

This science use case example was generated using APT version 25.2.3. You may encounter some differences in the user interface if you load the file in the latest version of APT.




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