JWST's FGS Internal Flat template, available in the Astronomer’s Proposal Tool (APT), has parameters for specifying and scheduling observations.

Introduction

The FGS Internal Flat template is to be used for all observations using the internal flat 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. 

There is an implicit PCSMODE = COARSE for these observations. Visit duration may not be longer than the maximum Coarse-mode value (currently 1800 seconds) measured from the start of the first Small Angle Maneuver (SAM).

Internal flats are obtained with illumination from one of the FGS calibration lamps (although the sky is being detected since there is no shutter). Exposures with predefined parameters are taken at each pointing in the specified dither pattern.

The FGS Internal Flat 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, and Special Requirements.

Target Name  

  Select the TARGET NAME [TBD] from the list of targets previously entered (see list of targets).

Detector 

DETECTOR [DETECTOR] = GUIDER1, GUIDER2

This field specifies the detector to be used to obtain the data.

Calibration Type 

CALIBRATION TYPE [CALIB_TYPE] = FULLONLY, WITHSUBARRAYS

This field specifies the calibration type to be performed.  If FULLONLY is selected, only full-frame exposures will be taken.  If WITHSUBARRAYS is selected, exposures of a set of 9 calibration subarrays will also be taken along with the full-frame exposures at each pointing in the dither pattern.

Primary Dithers

PRIMARY DITHERS [PRIMARY_DITHERS] = 1, 2

This parameter specifies the number of primary dither points.

Subpixel Positions

SUBPIXEL POSITIONS [SUBPIXEL_POSITIONS] = 1, 2

This parameter specifies the secondary dither points used for every primary dither point.

Note for developer: The table below specifies the sequence of exposures at each pointing when the calibration type is WITHSUBARRAYS.  The NUMBER OF INTEGRATIONS/EXPOSURE is 5 and the NUMBER OF GROUPS/INTEGRATION is 10 for all Internal Flat exposures.  The placeholder character n in aperture names refers to the guider in use (1 or 2).  For the FULLONLY calibration type, only the first (full-frame) exposure is performed at each pointing.  The list of FGS apertures can be found in Appendix H4 and the readout pattern definitions can be found in Appendix D.

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