NIRSpec Bright Object Time Series Template Parameters
JWST's NIRSpec Bright Object Time Series 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 NIRSpec Bright Object Time Series template is to be used for all observations using the bright object mode of NIRSpec, and this article describes allowed values for all parameters. Advice on how to choose values which optimize your science can be found in the NIRSpec Bright Object Time-Series APT Template article and in NIRSpec Bright Object Time-Series Spectroscopy.
The NIRSpec Bright Object Time Series 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 | |
| Special Requirements | specify special requirements | choose from list | if needed |
| Template Specific Information | |||
| Target Acquisition Parameters | |||
| Target Acquisition Method | select target acquisition method | NONE, WATA | |
| WATA Target Acquisition Parameters | |||
| Acquisition Target | select acquisition target | choose from list | |
| Acquisition Subarray | select subarray | choose from list | |
| Acquisition Filter | select filter | choose from list | |
| Acquisition Readout Pattern | select readout pattern | choose from list | |
| Science Parameters | |||
| select subarray | choose from list | ||
| select grating/filter name | choose from list | ||
| Number of Exposures/Dither | specify the number of times to repeat the exposure at each dither position | number | |
| select readout pattern | choose from list | ||
| specify number of groups per integration | number | ||
| specify number of integrations per exposure | number | ||
Note for developer: This template cannot be used in parallel and cannot have parallels attached to it; the NO PARALLEL special requirement should be added. The TIME SERIES OBSERVATION special requirement should also be added.
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, and Special Requirements.
Target Acquisition Parameters
Target Acquisition (TA) Method
TA METHOD [TA METHOD] = NONE, WATA (default)
For NIRSpec Bright Object Time Series spectroscopy there are two options: NONE which performs no target acquisition, or Wide Aperture Target Acquisition (WATA) that observes the target or a reference object through the wide aperture, and calculates an offset to the science aperture to be applied to the subsequent science exposures.
Select the target acquisition method to be used; see BOTS Template Section 3: Target Acquisition Parameters. When roll correction is not required, WATA provides a means to acquire a target or a reference target without the need for Reference Stars.
Note that WATA can be used for moving targets, but offset acquisition targets are not allowed when the science target for time series spectroscopy is a moving target. The acquisition target must be the same as the science target in that case.
Note for developers: TA METHOD is a required parameter. If WATA is selected, APT should accept WATA Target Acquisition parameters below.
WATA Target Acquisition Exposure
If TA METHOD = WATA, the wide aperture target acquisition places the acquisition target (which may be the science target) into the NIRSpec wide aperture. A target acquisition exposure is taken through this aperture to derive a centroid, to center the acquisition target in this wide aperture. After the target acquisition completes, a “reference image” of the acquisition target centered in the wide aperture is obtained to allow observers to check the status of the acquisition after the fact. Following that, the spacecraft will be repointed to put the science target in the aperture prior to the start of the science exposures; see BOTS Template Section 3: Target Acquisition Parameters .
For this method of TA, the following parameters are used to define NIRSpec Target Acquisition observations.
Acquisition Target
The default for this parameter is "Same Target as Observation." If instead of the target of the observation, an offset star is to be used for the target acquisition, select the ACQUISITION TARGET [TACQ TARGET] from the list of targets previously entered.
Note that for observations of moving targets, the ACQUISITION TARGET cannot be an offset target.
Notes for developers:
- For APT, the ACQUISITION TARGET field should always be present, but should be defaulted to SAME TARGET AS OBSERVATION.
- If the acquisition target is different from the science target, APT should provide a warning if the slew distance between the ACQ pointing (to place the acquisition target into the S1600A1 aperture) and Science pointing (to place the science target into the same aperture) is greater than the Visit splitting distance found in the PRD.
- If there are multiple pointings within a visit, then the rules have to apply to the greatest separation between acquisition target and pointing within the visit.
Acquisition Subarray
TARGET ACQUISITION SUBARRAY [TACQ SUBARRAY] = SUB32 (default), SUB2048, FULL
This field specifies the subarray region on the detector to be used to obtain the acquisition data.
Acquisition Filter
TARGET ACQUISITION FILTER [TACQ FILTER] = F140X, F110W, CLEAR
This field specifies the filter to be used to obtain the acquisition data.
Acquisition Readout Pattern
TARGET ACQUISITION READOUT PATTERN [TACQ PATTERN] = NRSRAPID (default), NRSRAPIDD6
This field specifies the readout pattern to be used to obtain the acquisition data.
Note that the TARGET ACQUISITION NUMBER OF GROUPS/INTEGRATION is automatically set to 3 and TARGET ACQUISITION NUMBER OF INTEGRATIONS/EXPOSURE is automatically set to 1.
Science Parameters
Subarray
SUBARRAY [SUBARRAY] = SUB512, SUB512S, SUB1024A, SUB1024B, SUB2048
This parameter specifies the region of the detector that is to be read out. For details, see Subarray in Table1 of the NIRSpec Bright Object Time-Series APT Template article.
Grating/Filter
GRATING/FILTER [GRATING, FILTER] = G140M/F070LP, G140M/F100LP, G235M/F170LP, G395M/F290LP, G140H/F070LP, G140H/F100LP, G235H/F170LP, G395H/F290LP, PRISM/CLEAR
Select the name of the grating/filter combination you wish to use for the science observations. For the grating/filter bandpasses, see NIRSpec Dispersers and Filters.
Number of Exposures/Dither
NUMBER OF EXPOSURES/DITHER [NEXP] specifies the number of exposures at each dither point. The maximum NUMBER OF EXPOSURES/DITHER is 50.
Exposure Specification
For each exposure, specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, and NUMBER OF INTEGRATIONS/EXPOSURE.
Readout Pattern
READOUT PATTERN [READOUT PATTERN] = NRS, NRSRAPID (default)
This field specifies the readout pattern to be used to obtain the science data.
Number of Groups/Integration
NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in an integration. The maximum NUMBER OF GROUPS/INTEGRATION is 65535.
Number of Integrations/Exposure
NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated. The maximum NUMBER OF INTEGRATIONS/EXPOSURE is 65535.