JWST's MIRI Coronagraphic Imaging template, available in the Astronomer’s Proposal Tool (APT), has parameters for specifying and scheduling observations.

Introduction

The MIRI Coronagraphic Imaging template is to be used for all observations using the coronagraphic imaging mode of MIRI, and this article describes allowed values for all parameters. Advice on how to choose values which optimize your science can be found in the MIRI Coronagraphic Imaging APT Template article and in MIRI Coronagraphic Imaging.

The MIRI Coronagraphic Imaging template consists of the following parameters:

General Information 

 The following parameters are generic to all templates, and are not discussed in this article: Observation Number,  Observation Label, Observations Comments, Target Name, ETC Wkbk. Calc. ID, and Special Requirements. 

Target Acquisition Parameters

The following parameters are used to define MIRI Target Acquisition observations. Note that for Coronagraphy, the science target is generally used for the acquisition, although when necessary, an offset star may be used. For more information on defining a target acquisition specification, see MIRI Coronagraphic Imaging Target Acquisition.

Acquisition Target 

The ACQUISITION TARGET parameter is used to define MIRI Target Acquisition observations. Select the ACQUISITION TARGET [TACQ TARGET] from the list of targets previously entered. The exception is when the target is a background target for which target acquisition is not allowed (see Special Handling of Background Targets below). 

Special Handling of Background Targets

When the science target is a background target:

• ACQUISITION TARGET is set to NONE and the other target acquisition parameters are hidden.
• The BACKGROUND QUADRANT parameter becomes available.
• DITHER TYPE is set to NONE (or BACKGROUND if REPEAT OBSERVATION is also selected) and cannot be changed.
• The PSF Reference Observation section is hidden.

When the science target is linked to a background target:

 For each science or PSF Reference Observation of that science target using a distinct mask/filter, there must exist a background observation of that background target that meets all of the following criteria:

• The background observation must be in the proposal (error if not).
• The background observation must be linked in a SEQUENCE NON-INT or GROUP NON-INT special requirement with the science observation (error if not).
•  The background observation must use the same mask/filter as the science observation (error if not).

  All background observations linked to a PSF Reference Observation will have EXCLUSIVE ACCESS PERIOD = 0. 

Note for developers: Target acquisition with the LYOT coronagraph will use the MASKLYOT subarray. With the 1550 4QPM will use the MASK1550 subarray. Same for 1140 and 1065.

Acquisition Filter 

ACQUISITION FILTER [TACQ FILTER] = F560W, F1000W, F1500W, FND

This parameter specifies the ACQUISITION FILTER to be used for the target acquisition.

Acquisition Readout Pattern    

READOUT PATTERN [TACQ PATTERN] = FAST (default), FASTGRPAVG, FASTGRPAVG8, FASTGRPAVG16, FASTGRPAVG32, FASTGRPAVG64

This field specifies the readout pattern to be used to obtain the acquisition data. 

Acquisition Number of Groups/Integration     

NUMBER OF GROUPS/INTEGRATION[TACQ NGROUPS] = 4, 6, 8, 10, 12, 22, 36, 44, 66, 86, 98

This field specifies the number of groups in an integration.

Acquisition Number of Integrations/Exposure

The NUMBER OF INTEGRATIONS/EXPOSURE [TACQ NINTS] is set to 1 for target acquisition observations.

Acquisition Quadrant  

TACQ QUADRANT [TACQ QUADRANT]= 1, 2, 3, 4

Select the quadrant in which the initial target acquisition will be performed. When the science target is a background target, this parameter is not available.

Coronagraphic Parameters

For the exposures to be executed, specify the MASK/FILTER, READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, NUMBER OF INTEGRATIONS/EXPOSURE, and theNUMBER OF EXPOSURES/DITHER.For more information on defining an exposure specification, see  Exposure time in the MIRI Coronagraphic APT Template article. Optional DITHER TYPE and REPEAT OBSERVATION may also be selected.   

Note for developers: Observations with this template must fit into a single visit. If more than one visit is created for an observation, give an error.

Background Quadrant  

BACKGROUND QUADRANT [BACKGROUND QUADRANT]= 1, 2, 3, 4

Select the quadrant in which the background target will be placed. This parameter is only available when the science target is a background target.

Coronagraphic Mask/Filter Combination

CORONAGRAPHIC MASK[CORON]/FILTER[FILTER] = 4QPM/F1065C, 4QPM/F1104C, 4QPM/F1550C, LYOT/F2300C

Select the coronagraphic mask  and filter  combination you wish to use to obtain the data; for the mask properties, see MIRI Coronagraph Masks, while for the filter bandpasses, see Coronagraphic filters in MIRI Coronagraphic Imaging.

Note for developers: The following SUBARRAY values are used for the specified mask: 4QPM/F1065C - MASK1065, 4QPM/F1104C- MASK1140, 4QPM/F1550C - MASK1550, and LYOT/F2300C - MASKLYOT.

Note for developers: for now, only 1 mask/filter can be selected for an observation.  However, in the future, it may be possible to use all 4. Also, APT will need to break the selection into their component values for the scripts. Also note that only 1 exposure time per Mask/Filter will be supported.

Subarray

SUBARRAY [SUBARRAY] = FULL, MASK1065, MASK1140, MASK1550, MASKLYOT

This parameter specifies the region of the detector that is to be read out. Also see Subarrays in MIRI Coronagraphic Imaging APT Template.

Available SUBARRAY options depend on the selected CORONAGRAPHIC MASK/FILTER as shown in Table 1.

Table 1. Subarray options for Mask/Filter combination

Readout Pattern

READOUT PATTERN[READOUT PATTERN] = FASTR1 (default), FASTGRPAVG

This field specifies the readout pattern to be used to obtain the data.

Number of Groups/Integration

NUMBER OF GROUPS/INTEGRATION[NGROUPS] specifies the number of groups in each integration. Allowed values are shown in Table 2.

 MIRI integration duration may not be greater than 2000 seconds. Integration time = (Frame time * NUMBER OF GROUPS/INTEGRATION). Frame time is a property of the selected READOUT PATTERN. For more information, see MIRI Detector Readout Overview.

Note to developer: Maximum MIRI integration duration is specified in the PRD as max_integration_duration_miri  in the observing_limitations table.

Table 2. Allowed values for NUMBER OF GROUPS/INTEGRATION

Number of Integrations/Exposure

NUMBER OF INTEGRATIONS/EXPOSURE[NINTS] field specifies the number of times the integration is repeated in each exposure; default = 1.

Number of Exposures/Dither 

NUMBER OF EXPOSURES/DITHER [NEXP]  specifies the number of times the exposure is to be repeated at each dither position. The default value is 1.

IfNUMBER OF EXPOSURES/DITHER > 1, the NO PARALLEL special requirement is required.

Note for developer: If NUMBER OF EXPOSURES/DITHER > 1. provide the following error: " The Special Requirement NO PARALLEL must be used with this Observation." and the following diagnostic explanation: "The NO PARALLEL requirement is required for Coordinated Parallels; Time Series observations; external observations with NUMBER OF EXPOSURES/DITHER > 1 and dithering; NIRSpec observations with Auto Calibrations; NIRCam Grism Time Series; and engineering templates (FGS Internal Flat, MIRI Anneal, MIRI External Flat, NIRSpec Internal Lamp, NIRSpec MSA Masking, NIRSpec MSA Anneal, NIRISS Internal Flat, all WFSC)." 

Dither Type

DITHER  TYPE [PATTERN_TYPE] = None (default), 5-POINT-SMALL-GRID, 9-POINT-SMALL-GRID, BACKGROUND

This parameter specifies the type of dithering needed. When the science target is a background target, DITHER TYPE is set to NONE (or BACKGROUND if REPEAT OBSERVATION is also selected) and cannot be changed.

Repeat Observation

REPEAT OBSERVATION = NO (default), YES

If REPEAT OBSERVATION=YES:

• If an ACQUISITION TARGET is selected, the target acquisition (followed by a science exposure) will be repeated starting in the quadrant diagonally across the central spot from the initial TARGET ACQUISITION QUADRANT.
• If ACQUISITION TARGET=NONE, two exposures are executed: the first in the BACKGROUND QUADRANT, and a second exposure in the diagonal quadrant as shown in Figure 1.

Figure 1: Diagonal  Quadrants

Note for developer:

• When TARGET ACQUISITION QUADRANT has a valid value, show the text "(with Target Acquisition in quadrant X)" where X is the value of the diagonal quadrant.
•  Store the second TACQ QUADRANT value instead of this boolean in the database.

PSF Reference Observations

Coronagraphic observations generally have two science observations with an APERTURE PA OFFSET between them of 1-14 degrees as well as an associated PSF reference observation. These observations should be done back-to-back using a SEQUENCE NON-INT or GROUP NON-INT special requirement. Warnings and errors will help guide the user to correctly set up these links. When the target is a background target, the PSF Reference Observations parameters are not displayed.

This is a PSF Reference Observation

Choosing this option indicates the observation is a "designated PSF Reference Observation."

  All PSF Reference observations will have EXCLUSIVE ACCESS PERIOD = 0. 

Note to developer: If this option is chosen, display on the GUI "exclusive access period will be 0 months".

PSF Reference Observations

Select one or more observations from the list provided. The list includes all observations in the proposal which are observed with the same instrument, same CORONAGRAPHIC MASK, and same FILTER as the science observation. 

One or more observations must be selected, except when Proposal CATEGORY = CAL or ENG. The selected observation must be a "designated PSF Reference observation" (i.e., the THIS IS A PSF REFERENCE OBSERVATION option is selected), unless ADDITIONAL JUSTIFICATION is also selected.

Note to developer: In the list, observations should be ordered first with the ones that have This Is A PSF Reference Observation checked,  then the ones without the check.

Additional Justification

Choosing this option indicates that this observation will not have a "designated PSF Reference observation," because it is part of a self reference survey which will be described in the science justification. One or more PSF Reference Observations are still required. For more information see the "Special case: coronagraphic surveys" section in HCI APT Instructions.

Notes to developer:

• It is an error to have nothing checked in the PSF Reference Observations. And it is still an error for a science observation to only choose other science observations and not choose a designated PSF observation, but in that case choosing the Additional Justification option replaces that error with a warning that a self reference survey must be justified.
• If a "designated PSF Reference observation" is selected, Additional Justification is disabled.  
• If Additional Justification  is selected, it is un-selected when a designated observation with This Is A PSF Reference Observation checked is selected

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