MIRI Low Resolution Spectroscopy Template Parameters

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

Introduction

Purple text indicates the parameter is Limited Access.

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

(warning)Red text indicates restrictions on a parameter.

(red star) Black text indicates an important note.

Brown text indicates notes for the developers.

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

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

The MIRI Low Resolution Spectroscopy (LRS) template is to be used for all observations using the low resolution spectroscopy 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 LRS APT Template article.

The MIRI Low Resolution Spectroscopy template consists of the following parameters:

FieldDetailsValues Notes
General Information   
Observation Numberassign observation number

number



Observation Label provide observation labeltextoptional
Observation Commentsprovide observation commentstextoptional
Target Nameselect Target Namechoose from listfrom Target List

ETC Wkbk. Calc. ID

specify ETC Workbook Calculation IDnumberfor science exposures (optional) and target acquisition exposures
Mosaic Propertiesspecify mosaic parametersnumberif needed
Special Requirementsspecify special requirementschoose from listif needed
Template Specific Information   
Target Acquisition Exposure
Acquisition Targetselect acquisition targetchoose from list
Acquisition Filterselect filter namechoose from list
Acquisition Readout Patternselect acquisition readout patternchoose from list
Acquisition Number of Groups/Integrationselect number of groups per integrationchoose from list
Acquisition Number of Integrations/Exposureselect number of integrations per exposure1only allowed value
LRS Parameters
Obtain verification image?select option for verification imageYES, NOoptions available only when TACQ_TARGET is the science target and SUBARRAY = FULL.
Pointing Verification Filter
select filter for verification imagechoose from list 
Pointing Verification Exposure
PV Readout Pattern
select PV readout patternchoose from list 
PV Number of Groups/Integrationselect PV number of groups per integrationchoose from list 
PV Number of Integrations/Exposureselect PV number of integrations per exposurechoose from list 
Science Exposures
Subarrayselect subarraychoose FULL or SLITLESSPRISM
Dither Specifications
Dither Typeselect dither typechoose from list
Number of Spectral Stepsenter number of spectral steps1, 2, 3, ...for DITHER TYPE=MAPPING only
Spectral Step Offsetenter offset per spectral stepany positive numberfor DITHER TYPE=MAPPING only
Number of Spatial Stepsenter number of spatial steps1, 2, 3, ...for DITHER TYPE=MAPPING only
Spatial Step Offsetenter offset per spatial stepany positive numberfor DITHER TYPE=MAPPING only
Readout Patternselect readout patternchoose from list
Number of Groups/Integration

specify number of groups per integration

number
Number of Integrations/Exposure

specify number of integrations per exposure

number
Number of Exposures/Ditherspecify number of times to repeat the exposure for each dither positionnumber

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, Mosaic Properties, and Special Requirements.

Target Acquisition Parameters

The following parameters are used to define MIRI Target Acquisition observations. Note that for Low Resolution Spectroscopy, the science target is generally used for the acquisition, although when necessary, an offset star may be used. For more information, see MIRI LRS Slit Target Acquisition.

Acquisition Target 

The default for this parameter is "Same Target as Observation." If an offset star is to be used for the target acquisition observation, select the ACQUISITION TARGET NAME [TACQ TARGET] from the list of fixed targets previously entered. When the science target is a Solar System target, the acquisition target MUST be the science target. Or, if no target acquisition is needed, select ACQUISITION TARGET to be NONE. (warning) NONE is not allowed when SUBARRAY=SLITLESSPRISM

Note for developers: LRS target acquisition will use the FULL array.

Acquisition Target Filter 

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

This parameter specifies the TARGET 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. (warning) When SUBARRAY=FULL, the only values available are 4, 6, 8, 10.

Acquisition Number of Integrations/Exposure 

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

LRS Verification Image

Obtain Verification Image?

OBTAIN VERIFICATION IMAGE = YES, NO (default)

If OBTAIN VERIFICATION IMAGE = YES, an additional image is obtained for pointing verification using the PV FILTER  and the PV exposure parameters, which may be different from the target acquisition filter and parameters.

Pointing Verification Filter

PV FILTER=F560W, F770W, F1000W, F1130W, F1280W, FND, F1500W, F1800W, F2100W, F2550W

This field specifies the filter used for the pointing verification image.

Pointing Verification Exposure 

PV Readout Pattern 

PV READOUT PATTERN = FASTR1 (default), SLOWR1, FASTGRPAVG

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

(warning) SLOWR1 is allowed only when SUBARRAY=FULL.

PV Number of Groups/Integration

PV NUMBER OF GROUPS/INTEGRATION[NGROUPS] specifies the number of groups in an integration. Allowed values are shown in Table 1.

(warning) 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.

PV Number of Integrations/Exposure

PV NUMBER OF INTEGRATIONS/EXPOSURE[NINTS] field specifies the number of times the integration is repeated. The default value is 1.

Science Exposures   

Subarray 

SUBARRAY [SUBARRAY] = FULL, SLITLESSPRISM

This parameter specifies the region of the detector to be read out.  For more details about these subarrays, see Subarray in the MIRI LRS APT Template article.

When SUBARRAY = SLITLESSPRISM the TIME SERIES OBSERVATION and NO PARALLEL special requirements are  added by default. Note that since time series observations cannot have parallels attached, the  NO PARALLEL special requirement is required. 

Dither Specifications 

Most MIRI LRS observations will require dithering; see MIRI LRS Dithering for details. Note that the dither pattern does NOT apply to the target acquisition image.

Dither Type 

DITHER TYPE [PATTERN_TYPE] = NONE, ALONG SLIT NOD, MAPPING, 1-PIXEL SLIT SCAN, 2-PIXEL SLIT SCAN, 7-PIXEL SLIT SCAN, 7X3 PIXEL MAP CENTER, 7X3 PIXEL MAP NOD1, 7X3 PIXEL MAP NOD2, INTRAPIXEL SLIT SCAN CENTER, INTRAPIXEL SLIT SCAN NOD1, INTRAPIXEL SLIT SCAN NOD2, LONG CROSS SCAN CENTER, LONG CROSS SCAN NOD1, LONG CROSS SCAN NOD2, SHORT CROSS SCAN CENTER, SHORT CROSS SCAN NOD1, SHORT CROSS SCAN NOD2, 7PIX + 5PIX SLIT SCAN, 1-PIXEL SLITLESS SCAN LONG, 1-PIXEL SLITLESS SCAN SHORT, 2-PIXEL SLITLESS SCAN SHORT, 7X3 PIXEL MAP SLITLESS, 7-PIXEL 9X3 MAP SLITLESS, 5-PIXEL 8X4 MAP SLITLESS, 7-PIXEL SLITLESS SCAN, 5-PIXEL SLITLESS SCAN, INTRAPIXEL SLIT SCAN CENTER, EXTENDED FLAT SLITLESS

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

Notes for developer:

  • When SUBARRAY=SLITLESSPRISM, the TSO special requirement is added by default (but may be removed by the user). 
  • When SUBARRAY=FULL  Slitless dither types are not available.
  • Slitless dither types are also not available when the TIME SERIES SPECIAL REQUIREMENT is present.

Along Slit Nod 

This option selects a pattern for point sources.  Two exposures are taken, one at each of two points along the slit.  No further parameters are required.

Mapping 

This option selects a grid pattern of dither points.  The following additional parameters are required.

Number of Spectral Steps 

NUMBER OF SPECTRAL STEPS[NUMBER_OF_SPECTRAL_STEPS] = 1, 2, 3, …

This parameter specifies the number of steps in the spectral direction.

Spectral Step Offset 

This parameter specifies the offset per step in the spectral direction.  The offsets are given in arcseconds, and can be any positive floating point value.

Number of Spatial Steps 

NUMBER OF SPATIAL STEPS[NUMBER_OF_SPATIAL_STEPS]= 1, 2, 3, …

This parameter specifies the number of steps in the spatial direction.

Spatial Step Offset 

This parameter specifies the offset per step in the spatial direction.  The offsets are given in arcseconds, and can be any positive floating point value.

Note for developers: see MIRI Dithering Details for dithering details.

Exposure Specifications    

For each exposure to be executed at each position in a dither pattern, specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, NUMBER OF INTEGRATIONS/EXPOSURE, and the  NUMBER OF EXPOSURES/DITHER. For more information on defining an exposure specification, see Exposure time in the MIRI LRS APT Template article.

Readout Pattern 

READOUT PATTERN [READOUT PATTERN] = FASTR1 (default), SLOWR1, FASTGRPAVG

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

(warning) SLOWR1 is allowed only when SUBARRAY=FULL.

Number of Groups/Integration

NUMBER OF GROUPS/INTEGRATION[NGROUPS] specifies the number of groups in an integration. Allowed values are shown in Table 1.

(warning) 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 1. Allowed values for NUMBER OF GROUPS/INTEGRATION

When readout pattern isValue of NUMBER OF GROUPS/INTEGRATIONAllowed?
FASTR1, SLOWR1, FASTGRPAVG1Not allowed (error)
FASTR1, SLOWR12Allowed with permission  (see Limited Access Parameters)
FASTGRPAVG2,3Allowed but not recommended (warning)
FASTGRPAVG>3Allowed
FASTR1, SLOWR13,4Allowed but not recommended (warning)
FASTR1, SLOWR1>4Allowed

Number of Integrations/Exposure

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

(warning)If NUMBER 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)." 

Change log

 

  1. PROPINSTJWST-91602 Updated filter list in Pointing Verification Filter section.


February 27, 2023

  1. PROPINSTJWST-91430  Updated LRS Verification Image section Added Pointing Verification Exposure section.


July 15, 2022

  1. PROPINSTJWST-91521 Changed text color of NUMBER OF EXPOSURES/DITHER section to purple to indicate LAP.


May 16, 2022

  1. PROPINSTJWST-91486  Added red note for error to Acquisition Target section.


Version 16 (May 6, 2022)

  1. PROPINSTJWST-91468 In Acquisition Target section developer note, removed developer note about visit splitting error.


Version 15 (October 19, 2021)

  1. PROPINSTJWST-91491 Updated Readout Patterns section with new patterns; updated Table 2.


Version 14 (May 2, 2021)

  1. PROPINSTJWST-91406 Added table of allowable values for NUMBER OF GROUPS/INTEGRATION.
  2. PROPINSTJWST-91407 Added restriction that integration duration must be less than 2000 seconds.
  3. Editorial change - Anchor links fixed in parameter table by removing pagename from link.


Version 13 (September 1, 2020)

  1. PROPINSTJWST-90820 Updated Dither Types section with 25 new LAP Dither Types.                                     


Version 12 (November 26, 2019)

  1. PROPINSTJWST-91421  added LRS Parameters section.


Version 11 (September 23, 2019)

  1. PROPINSTJWST-91395 - added new Acq Readout Pattern options.


Version 10 (June 17, 2019)

  1. PROPINSTJWST-91381 - updated Acquisition Number of Groups/Integration section.


Version 9 (April 18, 2019)

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


Version 8 (December 21, 2018)

  1. PROPINSTJWST-91122 - added developer note  in Acquisition Target section restricting acquisition target options for fixed vs. solar system observations.
  2. PROPINSTJWST-87189 - removed SLOW option from acq readout.


Version 7 (August 10. 2018)

  1. PR 89798 - Updated Acquisition Number of Groups/Integration section.


Version 6 (May 14, 2018)

  1. PR 89879 - NO PARALLEL special requirement required for external observations with NEXP>1, added red note and developer note.

    PR 89323 - Updated red notes in Number of Groups/Integration for FASTGRAVP


Version 5 (December 27, 2017)

  1. PR 89483 - added restriction on Acq Target for SS observations
  2. PR 88411 - added note about TSO requirement and NO PARALLEL
  3. PR 86278 - added option for no target acquisition


Version 4 (November 20, 2017)

  1. PR 87189 - updated readout pattern SLOW to be non-LAP
  2. PR 87895 - updated Exposure field labels to Groups/Integration and Integrations/Exposure
  3. PR 88896 - made TA Number of Groups/Integration be a picklist


Version 3 (May 11, 2017)

  1. PR 85610 - renamed Dither Types


Version 2 (January 16, 2017)

  1. PR 85608 - updated TA parameters
  2.  PR 85922 - renamed SUBPRISM to SLITLESSPRISM
  3. PR 80734 - added Number of Exposures parameter    
  4. PR 85925 - set default Readout Pattern
  5. PR 85925 - added restriction on Number of Groups 
  6. PR 85863 - updated developer note for Acquisition Target
  7. PR 85608 - removed statement about Acq Flux
  8. PR 81292 - removed inconsistency in name of dither parameters


Version 1 (May 6, 2016)

This is the converted Word File from Chapter 11.