JWST's NIRCam Wide Field Slitless Spectroscopy (WFSS) imaging template, available in the Astronomer’s Proposal Tool (APT), has parameters for specifying and scheduling observations.

Introduction

The NIRCam Wide Field Slitless Spectroscopy (WFSS) template is used for the WFSS mode of NIRCam, and this article describes allowed values for all parameters. Advice on how to choose values which optimize your science can be found in the NIRCam Wide Field Slitless Spectroscopy APT Template.

The NIRCam WFSS 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, Observation Comments, Target Name, ETC Wkbk. Calc. ID, Mosaic Properties, and Special Requirements.

Modules  

See also: NIRCam Apertures

MODULES [MODULES] = ALL, A

This field specifies the module(s) to be used for both the WFSS grism exposures and the direct image exposures. 

For MODULES=ALL:

• Grism and direct image exposures will be taken simultaneously with Module A and with Module B. Module B cannot be used alone.
• The default target location is in the gap between the modules (APT provides a warning).

Subarray  

The SUBARRAY [SUBARRAY] parameter specifies the region of the SCA detector that is to be read out. FULL is the only allowed value.

Grism 

GRISM (LONG WAVELENGTH) [GRISM] = GRISMR, GRISMC, BOTH

This field specifies the long wavelength grism(s) to be used for the exposures. If GRISM=BOTH is specified, then two sets of science grism exposures will be acquired - once using GRISMR (the row grism), then using GRISMC (the column grism).

Note for developers: If only GRISMR or GRISMC is selected, provide the following warning: "Use of only one of GRISMR or GRISMC may result in spectral overlap from multiple sources that can't be corrected. Users should address this issue in their proposal text." 

Show partial spectra region in Aladin

Select this box to temporarily show Partial Spectra regions in Aladin. Clear this box to show Complete Spectra regions in Aladin.

• Complete Spectra: includes only sources whose complete spectra will fall on the detector for the given filter.
• Partial Spectra: includes the larger set of sources for which any of their dispersed spectra will fall on the detector for the given filter.

For Wide Field Slitless Spectroscopy observations with NIRCam, the instrument FOV is deflected significantly depending on which filter is used in combination with the LW Grism. The Aladin visualization tool displays the effective aperture size according to the selected filters.Aladin's filter dependent aperture rendering is designed to highlight which sources, when dispersed by the grism, will have all of their spectra fall on the detector (or part of their spectra if 'Show partial spectra region' is selected).

Dither Patterns  

Most NIRCam WFSS imaging observations will require dithering; for details see Dither parameters in the NIRCam Wide Field Slitless Spectroscopy APT Template article. 

Primary Dither Type  

PRIMARY DITHER TYPE [DITHER_FOV] = NONE, INTRAMODULE, INTRAMODULEBOX, INTRAMODULEX

This parameter specifies the type of primary dither pattern.

For observations with a single dither point, APT provides a warning. Total Dithers are displayed on the Filters table. The warning is not provided if the NIRCam Imaging observation is in a pure parallel, or is non-prime in a coordinated parallel with a prime that is not dithered.

Note for developers: PRIMARY DITHER TYPE should be a required field, and there should be no default value (i.e. do not make NONE the default).

None   

This value indicates no dithering will be performed.

Intramodule   

The following parameter is needed to specify the INTRAMODULE dither. 

Primary Dithers    

PRIMARY DITHERS [PRIMARY_DITHERS] = 3, 4, 6, 8, 12, 16

This parameter specifies the number of primary dither points.

Intramodulebox  

The following parameter is needed to specify the INTRAMODULEBOX dither. 

Primary Dithers    

PRIMARY DITHERS [PRIMARY_DITHERS] = 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16

This parameter specifies the number of primary dither points.

Intramodulex  

The following parameter is needed to specify the INTRAMODULEX dither. 

Primary Dithers    

PRIMARY DITHERS [PRIMARY_DITHERS] = 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16

This parameter specifies the number of primary dither points.

Subpixel Positions  

SUBPIXEL POSITIONS [SUBPIXEL_POSITIONS] = 2-point, 4-point, 9-point, NONE

This parameter specifies the secondary dither points used for every primary dither point and is required for all PRIMARY DITHER TYPE values, including NONE.

Note for developers: see NIRCam Dither Details for dithering details.

Science (Grism) Exposure

For each grism science exposure the following exposure parameters will be required. If GRISM=BOTH was chosen, all the specified exposures using/supporting GRISMR will be executed, then all the same specified exposures using/supporting GRISMC will be executed. Each complete set of exposures for a requested grism includes requested dithers, and (optionally) direct images.

Note for developers: The GRISM(s) chosen will be populated into the long wavelength pupil.

Long Wavelength Filter   

LONG FILTER [FILTLONG] = F277W, F322W2, F356W, F444W, F250M, F300M, F335M, F360M, F410M, F430M, F460M, F480M

This field specifies the filter to be used for the long wavelength science grism exposures. For more details on the Filters, see Science in the NIRCam Wide Field Slitless Spectroscopy APT Template article.

Short Wavelength Filter   

SHORT FILTER [FILTSHORT] = F140M, F162M+F150W2, F164N+F150W2, F182M, F187N, F210M, F212N, F070W, F090W, F115W, F150W, F200W

This field specifies the filter to be used for the short wavelength science imaging exposures.

Note for developers: The filters F162M and F164N are actually on the pupil wheel so they are paired with filter F150W2; the pupil wheel is CLEAR for all other values.

Exposure Duration  

For each exposure specification, choose the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, and the NUMBER OF INTEGRATIONS/EXPOSURE. For more information on defining an exposure specification, see Science in the NIRCam Wide Field Slitless Spectroscopy APT Template article.

Readout Pattern   

READOUT PATTERN [READOUT PATTERN] = RAPID, BRIGHT1, BRIGHT2, SHALLOW2, SHALLOW4, MEDIUM2, MEDIUM8, DEEP2, DEEP8

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

Number of Groups/Integration   

NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in each integration. If MODULES=ALL, see Table 1. If MODULES=A, the range is 1-10 for all patterns.

 Table 1.  Number of Groups/Integration for WFSS Observations (MODULES=ALL)

Number of Integrations/Exposure   

NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated within an exposure.  If MODULES=ALL, see Table 1. If MODULES=A, the range is 1-10 for all patterns.  

Direct Image Exposures  

For each science exposure (except the last one, for which it is required) an optional Direct Image Exposure may be selected.

Note for developers: The Direct Images are not dithered.

Acquire Direct Image  

If checked, this field indicates that a direct image (no grism) is requested after this science exposure. The last science exposure specification must have this field checked. See Direct Images for details.

For each science image with Direct Image checked, the following direct image exposure parameters will be required.

Long Wavelength Filter   

LONG FILTER [FILTLONG] = F277W, F322W2, F356W, F444W, F250M, F300M, F335M, F360M, F410M, F430M, F460M, F480M

This field specifies the filter to be used for the direct long wavelength image exposures.

Short Wavelength Filter  

SHORT FILTER [FILTSHORT] = F140M, F162M+F150W2, F164N+F150W2, F182M, F187N, F210M, F212N, F070W, F090W, F115W, F150W, F200W

This field specifies the filter to be used for the direct short wavelength image exposures.

Note to developers:  The filters F162M and F164N are actually on the pupil wheel so they are paired with filter F150W2; the pupil wheel is CLEAR for all other values.

Direct Image Exposure Duration  

For each direct image exposure specification, choose the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, and the NUMBER OF INTEGRATIONS/EXPOSURE. For more information on defining an exposure specification, see Direct Images.

Direct Image Readout Pattern   

DIRECT IMAGE READOUT PATTERN [READOUT PATTERN] = RAPID, BRIGHT1, BRIGHT2, SHALLOW4, SHALLOW2, MEDIUM2, MEDIUM8, DEEP2, DEEP8

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

Direct Image Number of Groups/Integration   

DIRECT IMAGE NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in a direct image integration. If MODULES=ALL, see Table 1. If MODULES=A, the range is 1-10 for all patterns.

Direct Image Number of Integrations/Exposure   

DIRECT IMAGE NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the direct image integration is repeated within an exposure. If MODULES=A, the range is 1-10 for all patterns.

Out-of-Field Source Images 

After all of the requested Science and Direct Image Exposures are obtained for one of the grisms, two additional “Out-of-Field Source” direct images are taken using a predefined pattern of offsets. These images are required. The exposure specification is identical to the final Direct Image Exposure exposure specification. One pre-defined pattern is used at the end of a GRISMR sequence and a different pattern is used at the end of a GRISMC sequence.

Note for developers: GRISMR exposures use pattern GRISMR_SID and GRISMC exposures use pattern GRISMC_SID.

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