HST observations with WFC3 are specified using the Astronomer's Proposal Tool (APT), and this article provides instructions for completing those observations.

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

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.

Introduction

The Instrument Configurations and Operating Modes described in the following section are used to define exposures on the Visit and Exposure Specifications. The legal Visit and Exposure Specifications entries are summarized in the following sections. More complete descriptions of Instrument Configurations, Modes, Apertures, Spectral Elements, Detector Characteristics, etc. are available in the WFC3 Instrument Handbook.

Note that many of the Optional Parameters have default values; in such cases, an entry for an Optional Parameter in the Visit and Exposure Specifications is necessary only if it is desired to override the default value. The physical units of Optional Parameter quantities are always implicit and should never be entered by the observer.

Table 12.1 lists the permitted WFC3 Instrument Configurations, Operating Modes, Apertures, Spectral Elements, and Optional Parameters.

Table 12.1: Supported Instrument Parameters for WFC3

Config

Mode

Aperture

Spectral Elements

Optional Parameters

WFC3/UVIS

ACCUM

See Table 12.3: Apertures for WFC3/UVIS

See Table 12.22: Spectral Elements for use with WFC3/UVIS

CR-SPLIT, BIN, FLASH,
INJECT, BLADE, SIZEAXIS2, SIZEAXIS1, CENTERAXIS2, CENTERAXIS1, AMP, GAIN, CURRENT, CTE. FLASHEXP, FLASHCUR

WFC3/IR

MULTI ACCUM

See Table 12.4: Apertures for WFC3/IR

See Table 12.23: Spectral Elements for use with WFC3/IR

SAMP-SEQ, NSAMP, GAIN

For restricted parameters

Table 12.1: Parameters for WFC3 (Restricted)

Config.

Mode

Aperture

Spectral Elements

Optional Parameters

WFC3/UVIS,

WFC3/IR

ALIGN

FOCUS, TILT (Restricted)

WFC3

ANNEAL

For available but unsupported (Internal Calibration Targets)

Table 12.2: Internal Calibration Targets for WFC3 (Available but Unsupported)

Config

Target Name

Description¹

Spectral Element

WFC3/UVIS

BIAS

A CCD readout without an exposure (i.e., the exposure time must be specified as 0) in order to measure the detector bias level. GOs should request BIAS exposures only when needed to match external exposures taken with subarrays via optional parameters SIZEAXIS2 and/or SIZEAXIS1. STScI will provide BIAS reference files for all other situations (full-frame exposures or exposures obtained with a subarray aperture)².

To ensure the proper placement of the BIAS subarray with respect to the external exposure,

1. Specify the same Aperture on the BIAS exposure as on the external one.
2. Specify exactly the same subarray Optional Parameters on the BIAS exposure as on the external exposure.

To obtain a BIAS-like image for CTE EPER exposures, specify CTE=EPER, set the Target to DARK or DARK-NM and Time_Per_Exposure=0.5S.

DEF³

¹Only the GAIN, AMP, INJECT, BIN, CR-SPLIT, SIZEAXIS1, SIZEAXIS2, CENTERAXIS1, and CENTERAXIS2 Optional Parameters are permitted on BIAS exposures. (FLASH is not permitted.) CR-SPLIT may be specified only with the value NO. All BIAS exposures will be taken as single exposures (i.e., an implicit CR-SPLIT = NO will be applied).

²The Optional Parameters CENTERAXIS1 and CENTERAXIS2 may not have the value TARGET, nor may the Special Requirements POS TARG or PATTERN be specified with subarray BIAS exposures; STScI will not support such specifications.

³DEF means no change from the previous WFC3 UVIS exposure. The spectral element for BIAS exposures does not matter because the shutter is not opened.

For restricted (Internal Calibration Targets)

Table 12.2 (cont): Internal Calibration Targets for WFC3 (Restricted)

Config	Target Name	Description¹	Spectral Element
WFC3/UVIS	DARK	An exposure taken with the UVIS detector isolated from external light to measure the detector dark current.	DEF²
WFC3/UVIS	DARK-NM	A UVIS Dark exposure without the Channel Select Mechanism (CSM) being in a particular position and with the ability to specify a filter position.	Any element from Table 12.22: Spectral Elements for use with WFC3/UVIS
WFC3/UVIS	TUNGSTEN	An exposure taken with the UVIS detector with the Tungsten flat-field lamp powered on.	Any element from Table 12.22: Spectral Elements for use with WFC3/UVIS
WFC3/UVIS	DEUTERIUM	An exposure taken with the UVIS detector with the Deuterium lamp powered on.	Any element from Table 12.22: Spectral Elements for use with WFC3/UVIS
WFC3/IR	DARK	An exposure taken with the IR detector isolated from external light to measure the detector dark current.	BLANK³
WFC3/IR	DARK-NM	An IR Dark exposure without the CSM being in a particular position	BLANK
WFC3/IR	TUNGSTEN	An exposure taken with the IR detector with the Tungsten flat-field lamp powered on.	Any element from Table 12.23: Spectral Elements for use with WFC3/IR

¹Optional parameters SAMP-SEQ, NSAMP, CR-SPLIT, CURRENT, GAIN, AMP, BIN, INJECT, SIZEAXIS1, SIZEAXIS2 are permitted for all internal target exposures.
BLADE is allowed only for targets TUNGSTEN and DEUTERUIUM. CTE is allowed only if the target is TUNGSTEN, DARK-NM or DARK. CR-SPLIT may be specified only with the value NO. All internal target exposures will be taken as single exposures (i.e., an implicit CR-SPLIT = NO for UVIS exposures).

²DEF means no change from the previous WFC3 UVIS exposure. The spectral element for DARK exposures does not matter because the shutter is not opened.

³The spectral element for IR DARK exposures must be BLANK to block the light path to the detector.

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Change Log

Version Cycle 30 August 2022

Fix links in Table 12.1

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12.1 Introduction to WFC3

HST observations with WFC3 are specified using the Astronomer's Proposal Tool (APT), and this article provides instructions for completing those observations.

Format definitions

Introduction

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Table of Contents

Change Log

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