9.3.2 FGS Spectral Elements

There are several spectral elements allowed for HST's FGSs. This article provides a list of those spectral elements for the Astronomer's Proposal Tool (APT)

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Format definitions

Boldface type indicates the name of an APT parameter or a value for a parameter.

(red star) Black text indicates an important note.

Magenta text indicates available but unsupported parameters (requires prior approval from STScI).

Red text indicates restricted parameters (for STScI use only).

Brown text indicates text file parameters.

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

Table 9.2: Spectral Elements for the FGS

NameCommentsEffective Wavelength (Å)Full Width at Half Maximum (Å)
F583W “Clear” filter 58302340
F5NDNeutral Density (5 mag)........
F605W1“Astrometry Clear” filter 60501900
F650W2“Red” filter 6500750
F550W“Yellow” filter 5500750
PUPIL  Pupil stop58302340

1F605W is to be specified with FGS3 and FGS1.

2F650W is to be specified with FGS2 only.

Table 9.3: Restricted Internal Calibration Targets for the FGS

The following internal calibration targets are available for the FGS. These should not be included in your proposal if the routine calibrations are sufficient for your program (see the FGS Cycle 25 Calibration Plan Instrument Report). For further details see the FGS Instrument Handbook.

Table 2: Internal Calibration Targets for the FGS

Target Name Description Spectral ElementTime Per Exposure



The star selectors slew the FGS
Field of View off the Pickle
Aperture and the dark counts are
recorded for a time interval given
by the exposure time.
This occurs for target = DARK
for POS Mode.

Internal Test Source activated

AnyEnter a specific time

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PROPINST-91407- Improve the links to other documents.