NIRISS Focus Template Parameters
JWST's NIRISS Focus Engineering template, available in the Astronomer’s Proposal Tool (APT), is used for calibration observations for the NIRISS instrument.
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.
These parameters are required to obtain Focus observations. Note that this type of observation cannot be obtained as a parallel to normal science observations.
The focusing mechanism will be scanned through the specified number of relative positions centered on the current best focus, and then returned to the starting position. At each point in the focus sweep, an image will be obtained for analysis. If only one position is specified, the focus mechanism is moved to the specified position (i.e., the best focus position is reset).
The NIRISS Focus 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 |
| Special Requirements | specify special requirements | choose from list | if needed |
| Template Specific Information | |||
| select target name | choose from list | ||
| Filter | select filter name | choose from list | |
| Readout Pattern | select readout pattern | NIS, NISRAPID | |
| Number of Groups/Integration | specify number of groups per integration | number | |
| Number of Integrations/Exposure | specify number of integrations per exposure | number | |
| Relative Position | specify array of positions | array of 1-20 positions | |
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 , and Special Requirements.
Target Name
Select the TARGET NAME [TBD] from the list of targets previously entered; see list of targets.
Filter
FILTER [FILTER] = F090W, F115W, F140M, F150W, F158M, F200W, F277W, F356W, F380M, F430M, F444W, F480M
This parameter specifies the filter to be used for the exposure.
Exposure Specification
For each exposure specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, and NUMBER OF INTEGRATIONS/EXPOSURE.
Readout Pattern
READOUT PATTERN [READOUT PATTERN] = NIS, NISRAPID
This field specifies the readout pattern to be used to obtain the science data. NIS is used for faint targets, while NISRAPID is used for bright targets or scenes with high backgrounds.
Number of Groups/Integration
NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in an integration. For readout pattern NIS, the range is 1-200, while for NISRAPID the range is 1-30.
Number of Integrations/Exposure
NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated. The range is 1-10.
Relative Position
The RELATIVE POSITION [DELTARRAY] parameter specifies an array of 1 to 20 positions that the focus is to be moved to; note that each position must be unique (i.e., a given value can only appear once in the list). The positions are given in millimeters (range -9.0 to +9.0) in the OTE frame, and are offsets from the current position. The exact order in which the positions will be executed will be determined by the onboard scripts. There are 3 unique cases:
- to perform a focus sweep (returning to the original focus), enter from 2 to 20 positions
- to reset the focus, specify only 1 position
- to use the default scan (10 steps of -0.4mm from -2.0 to +2.0), select the checkbox
Note for developers: when the checkbox for default scan is selected, the Relative Position input area should be inactive.