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James Webb Space Telescope User Documentation

 

 

JWST's MIRI Multi-Instrument, Multi-Field Imaging template, available in the Astronomer’s Proposal Tool (APT), is used for calibration observations for the MIRI instrument.  

Introduction

MIRI Multi-Instrument, Multi-Field Imaging (MIMF) exposures are used to measure the PSF during wave-front sensing activities for commissioning of the JWST Optical Telescope Element (OTE). The MIRI MIMF observation will use a 5-points-of-light strategy to improve sampling of the PSF in multiple locations on the detector.  Those points are described in Table 1 below. At each of these points, the entire Dither pattern selected below will be executed.

Table 1. 5 Points-of-Light for MIRI MIMF Observations 

Image

X-Position (arcsec)

Y-Position (arcsec)

1

0

0

2

-66.0

56.32

3

66.0

56.32

4

66.0

-56.32

5

-66.0

-56.32

In addition to the following template parameters, this template will have the Special Requirement WAVEFRONT SENSING added with a default value of SENSING_ONLY, PCS MODE   with a value of TRACK, and DMS PRIORITY  with a value of HIGH .

Note for developers: This pattern will be implemented as a canned mosaic, and no further mosaic parameters should be allowed.  APT should default to include a NO PARALLEL special requirement when the template is created, but the user should be allowed to remove it if necessary.

The MIRI MIMF Imaging template consists of the following parameters:

FieldDetailsValues Notes
General Information   
Observation Numberassign observation number

number


 Observation Labelprovide observation labeltextoptional
Observation Commentsprovide observation commentstextoptional
Target Nameselect Target Namechoose from listfrom Target List
Special Requirementsspecify special requirementschoose from listif needed
Template Specific Information   

Dither Type

select dither typeCYCLING, REULEAUX 
Starting Pointspecify starting pointnumber (1, 2...310, 311)only if CYCLING is selected
 Number of Points specify number of dither positionsnumberonly if CYCLING is selected
Pattern Sizeselect pattern sizechoose from list
 Filter select filterF560W, F770W
Readout Patternselect Readout PatternFAST, SLOW
Number of Groups/Integrationspecify number of groupsnumber
Number of Integrations/Exposurespecify number of integrationsnumber

General Information  

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

Target Name

Select the TARGET NAME [TBD] from the list of targets previously entered (see list of targets).

Dither Pattern

MIRI MIMF Imaging observations with JWST will require dithering. The following parameters define the dither patterns for MIRI MIMF Imaging observations. The dither pattern will be executed at each of the points-of-light defined above.

Dither Type 

DITHER TYPE [PATTERN_TYPE] = CYCLING, REULEAUX

This parameter specifies the primary pattern to be used for dithering.

Cycling

The CYCLING pattern is shown in Figure (link to INS), and can be used to obtain data optimized for self-calibration at arbitrary sky depths. The pattern consists of a list of 311 pointing positions where the x- and y-offset distributions (from the central position) are well-described by a Gaussian; the pattern is drawn from the Spitzer IRAC Cycling pattern. Observations may begin at any position in the cycling pattern and include an arbitrary number of dithers. Each contiguous block of four pointing positions provides some 0.5 pixel sub-sampling in both the x- and y-directions. However, to provide optimized sub-pixel sampling, this pattern should be used in conjunction with the sub-pixel sampling option.

If the CYCLING pattern has been selected the following inputs are also required (along with PATTERN SIZE).

Starting Point 

STARTING POINT [STARTING_POINT] = 1, 2, 3, …, 310, 311

This parameter is used to determine the offset of the first dither position.

Number of Points 

NUMBER OF POINTS [NUMBER_OF_POINTS] = 3, 4, 5, …

This parameter indicates the total number of dither positions in the pattern. 

If the combination of STARTING POINT and NUMBER OF POINTS exceeds 311, the pattern cycles back to use points 1, 2, 3, etc. 

No explicit maximum is set on the number of points.  The number of points, however, is effectively limited by the maximum allowed visit duration.

Reuleaux

The REULEAUX pattern is shown in Figure (link to INS), and is optimized to provide to obtain observations of compact point sources that are suitable for self-calibration. The pattern is a set of 12 dither positions that defines a Reuleaux triangle; the pattern is drawn from the Spitzer IRAC 12-point Reuleaux pattern. The Reuleaux pattern includes some 0.5 pixel sub-sampling in both the x- and y-directions. However, to provide optimized sub-pixel sampling, this pattern should be used in conjunction with the sub-pixel sampling option.

If the REULEAUX pattern has been selected, you must also select a PATTERN SIZE.

Pattern Size 

PATTERN SIZE [PATTERN_SIZE] = DEFAULT (default), SMALL, MEDIUM, LARGE

This parameter specifies that all exposures are to be done with the same dithering pattern (SMALL, MEDIUM, or LARGE). When the pattern size is not specified by the user the DEFAULT pattern will be used based upon the choice of filter and pattern as indicated in Table 2.

Table 2. Default Dithering Pattern Sizes for MIRI MIMF Observations 

Filter

12-pt. Reuleaux

311-pt. Cycling

F560W

SMALL

SMALL

F770W

SMALL

MEDIUM

Note for developers: see Appendix F1 (link) for dithering details.

Filter Name 

FILTER [FILTER] = F560W, F770W

Select the name of one filter. 

Exposure Specifications 

For each exposure to be executed, specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, and NUMBER OF INTEGRATIONS/EXPOSURE.

Readout Pattern 

READOUT PATTERN [READOUT PATTERN] = SLOW, FAST

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 an integration.

Number of Integrations 

NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated.

Change log

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Version 2 (April 19, 2019)

  1. Editorial change (moved change log to main article)


Version 1 (April 10, 2017)

This is the converted Word File from Chapter 60.

Keywords

JWST MIRI Multi-Instrument, Multi-Field Imaging Template

JWST MIRI Multi-Instrument, Multi-Field Imaging template parameters

Format definitions

Boldface italics type indicates the name of an APT parameter or a value for a parameter.

Brown text indicates notes for the developers.

Green text indicates the name of the parameter used by Commanding.


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