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.
Red text indicates restrictions on a parameter.
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:
| Field | Details | Values | Notes |
|---|---|---|---|
| General Information | |||
| Observation Number | assign observation number | number | |
| Observation Label | provide observation label | text | optional |
| Observation Comments | provide observation comments | text | optional |
| Target Name | select Target Name | choose from list | from Target List |
| specify ETC Workbook Calculation ID | number | for science exposures (optional) and target acquisition exposures | |
| Mosaic Properties | specify mosaic parameters | number | if needed |
| Special Requirements | specify special requirements | choose from list | if needed |
| Template Specific Information | |||
| Target Acquisition Exposure | |||
| Acquisition Target | select acquisition target | choose from list | |
| Acquisition Filter | select filter name | choose from list | |
| Acquisition Readout Pattern | select acquisition readout pattern | choose from list | |
| Acquisition Number of Groups/Integration | select number of groups per integration | choose from list | |
| Acquisition Number of Integrations/Exposure | select number of integrations per exposure | 1 | only allowed value |
| LRS Parameters | |||
| Obtain verification image? | select option for verification image | YES, NO | options available only when TACQ_TARGET is the science target and SUBARRAY = FULL. |
| Pointing Verification Filter | select filter for verification image | choose from list | |
| Pointing Verification Exposure | |||
| PV Readout Pattern | select PV readout pattern | choose from list | |
| PV Number of Groups/Integration | select PV number of groups per integration | choose from list | |
| PV Number of Integrations/Exposure | select PV number of integrations per exposure | choose from list | |
| Science Exposures | |||
| Subarray | select subarray | choose FULL or SLITLESSPRISM | |
| Dither Specifications | |||
| Dither Type | select dither type | choose from list | |
| Number of Spectral Steps | enter number of spectral steps | 1, 2, 3, ... | for DITHER TYPE=MAPPING only |
| Spectral Step Offset | enter offset per spectral step | any positive number | for DITHER TYPE=MAPPING only |
| Number of Spatial Steps | enter number of spatial steps | 1, 2, 3, ... | for DITHER TYPE=MAPPING only |
| Spatial Step Offset | enter offset per spatial step | any positive number | for DITHER TYPE=MAPPING only |
| Readout Pattern | select readout pattern | choose 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/Dither | specify number of times to repeat the exposure for each dither position | number | |
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.
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. 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.
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.
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.
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.
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 is | Value of NUMBER OF GROUPS/INTEGRATION | Allowed? |
|---|---|---|
| FASTR1, SLOWR1, FASTGRPAVG | 1 | Not allowed (error) |
| FASTR1, SLOWR1 | 2 | Allowed with permission (see Limited Access Parameters) |
| FASTGRPAVG | 2,3 | Allowed but not recommended (warning) |
| FASTGRPAVG | >3 | Allowed |
| FASTR1, SLOWR1 | 3,4 | Allowed but not recommended (warning) |
| FASTR1, SLOWR1 | >4 | Allowed |
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.
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)."
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