FGS Focus
JWST's FGS Focus 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 FGS Focus template is to be used for all observations using the focus mode of the FGS, and this article describes allowed values for all parameters. Note that this type of observation cannot be obtained as a parallel to normal science observations.
The focusing mechanism will be scanned through a specified number of relative positions centered on the expected focus, and then returned to the starting position. At each point in the focus sweep, a wide-band image will be obtained for analysis. If only one position is specified, the focus is maintained at this new position (i.e. the focus is reset).
The FGS 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 |
| Target Name | select Target Name | choose from list | from Target List |
| Special Requirements | specify special requirements | choose from list | if needed |
| Template Specific Information | |||
| Detector | select detector | GUIDER1, GUIDER2 | |
| Readout Pattern | select readout pattern | FGS, FGSRAPID | |
| Number of Groups/Integration | specify number of groups per integration | number | |
| Number of Integrations/Exposure | specify number of integrations per exposure | number | |
| Relative Positions | 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, Observation Comments, and Special Requirements.
Target
Select the TARGET NAME from the list of targets previously entered.
Solar system targets may not be used with this template.
Detector
DETECTOR [DETECTOR] = GUIDER1, GUIDER2
This field specifies the detector to be used to obtain the data.
Exposure Specifications
For each exposure to be executed , specify the READOUT PATTERN, NUMBER OF GROUPS/INTEGRATION, and the NUMBER OF INTEGRATIONS/EXPOSURE.
Readout Pattern
READOUT PATTERN [READOUT PATTERN] = FGS, FGSRAPID
This field specifies the readout pattern to be used to obtain the data.
Number of Groups/Integration
NUMBER OF GROUPS/INTEGRATION [NGROUPS] specifies the number of groups in an integration.
Number of Integrations/Exposure
NUMBER OF INTEGRATIONS/EXPOSURE [NINTS] field specifies the number of times the integration is repeated.
Relative Positions
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 +26.73 to -26.73) 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.