10.1 Introduction to ACS

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

Expand/Collapse all...


On This Page

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.

Introduction

The Instrument Configurations and Operating Modes described in this chapter are used for the Visit and Exposure Specifications. The legal Visit and Exposure Specifications entries are discussed in the following sections. More complete descriptions of Instrument Configurations, Modes, Apertures, Spectral Elements, etc. are available in the ACS Instrument Handbook.

Many of the Optional Parameters have default values. In such cases an Optional Parameter entry in these Specifications is necessary only if it is desired to override the default value. In the STScI proposal system, the physical units of Optional Parameter quantities are always implicit and should never be entered by the observer.

The following tables list the permitted Instrument Configurations, Operating Modes, Apertures, Spectral Elements, and Optional Parameters for the ACS.

Table 10.1: Supported Instrument Parameters for the ACS

Config.ModeApertureSpectral ElementsOptional Parameters

ACS/WFC

ACCUM

WFC,
WFC-FIX,
WFC1,
WFC2,
WFC1-CTE,
WFC1-FIX,
WFC2-FIX,
WFCENTER,
WFC1-IRAMP,

WFC1-MRAMP,
WFC2-MRAMP,
WFC2-ORAMP,
WFC1-IRAMPQ,
WFC1-MRAMPQ,
WFC2-ORAMPQ,
WFC1A-512,
WFC1A-1K,
WFC1A-2K,
WFC1B-512,
WFC1B-1K,
WFC1B-2K,
WFC2C-512,
WFC2C-1K,
WFC2C-2K,
WFC2D-512,
WFC2D-1K,
WFC2D-2K

See Table 10.3: Spectral Elements for use with ACS/WFC Configuration

CR-SPLIT,
GAIN,
AUTOIMAGE,
FLASH

ACS/SBC

ACCUM

SBC,
SBC-FIX,
SBC-LODARK

See Table 10.7: Spectral Elements for use with ACS/SBC Configuration


For available but unsupported parameters

Config.ModeApertureSpectral ElementsOptional Parameters
ACS/WFCACCUMWFC1-512, WFC1-1K, WFC1-2K, WFC2-2K, WFC2-MRAMPQ
SIZEAXIS1, SIZEAXIS2, CENTERAXIS2, CENTERAXIS1, COMPRESSION, AMP

For restricted parameters

Config.ModeApertureSpectral ElementsOptional Parameters
ACS/WFCACCUM

CTE, FLASHCUR, FLASHEXP, READTYPE, SPEED

ACS/WFC

ALIGN

 

 

FOCUS, TILT

ACS/HRC

ALIGN

 

 

FOCUS, TILT

ACS

ANNEAL

 

 

 

For available but unsupported parameters

Table 10.2: Internal Calibration Targets for the ACS

Target NameDescription1Spectral Element

BIAS

A CCD readout without an exposure (i.e., the exposure time must be specified as 0) in order to measure the detector bias. Permitted only with the ACS/WFC in ACCUM mode.

GOs should request BIAS exposures only when needed to match external or lamp subarray exposures specified via Optional Parameters SIZEAXIS2 and/or SIZEAXIS1. STScI will provide BIAS reference files for other instances of ACS subarrays (i.e., when you specify F892N or a polarizer with a WFC exposure, or use a subarray aperture).

The following restrictions apply to subarray BIAS exposures:

Special Requirements POS TARG and PATTERN may not be specified, and Optional Parameters CENTERAXIS1 and CENTERAXIS2 may not have the value TARGET. STScI will not support such specifications.

To ensure proper location of a subarray BIAS exposure taken to match a subarray external or lamp exposure:

  1. Specify the Aperture to be the same as that of the external or lamp exposure.
  2. Provide identical subarray Optional Parameter Specifications.
  3. If a WFC external or lamp subarray exposure uses a ramp filter, specify the ramp filter also. See the ACS Instrument Handbook for more details. However, be aware that even though the ramp filter needs to be specified, it will not be used for the BIAS exposure. Instead, predefined filters will be used for the BIAS exposure. The specified ramp filter is used to determine the subarray center for the BIAS exposure.

DEF2 or any ramp filter in Table 10.3: Spectral Elements for use with ACS/WFC Configuration

1 Use of Optional Parameters with internal targets:

No Optional Parameters are permitted with ACS/SBC

All  internal  target  exposures  will  be  taken  as  single  exposures  (i.e., an implicit CR-SPLIT=NO).

Optional Parameters permitted with BIAS are: GAIN; COMPRESSION; AMP; SIZEAXIS2; SIZEAXIS1; CENTERAXIS2; CENTERAXIS1; READTYPE; SPEED.

2 DEF means the spectral element currently in place for the ACS/WFC, and means an opaque position for the ACS/SBC. For ACS/WFC Target Name BIAS, the spectral elements are predefined by the STScI ACS Instrument team.

For restricted parameters

Table 10.2 (cont). Internal Calibration Targets for the ACS

Target NameDescription3Spectral Element

DARK


An exposure taken with the detector shuttered from external light to measure the detector dark current. Permitted only with the ACS/WFC and ACS/SBC in ACCUM mode.

The following restrictions apply to subarray DARK exposures:

Special requirements POS TARG and PATTERN may not be specified and Optional Parameters CENTERAXIS1 and CENTERAXIS2 may not have the value TARGET. STScI will not support such specifications.

DEF4

TUNGSTEN


An exposure taken with the tungsten flat-field lamp. Permitted only with the ACS/WFC in ACCUM mode. The following restrictions apply to subarray TUNGSTEN exposures:

Special requirements POS TARG and PATTERN may not be specified and Optional Parameters CENTERAXIS1 and CENTERAXIS2 may not have the value TARGET. STScI will not support such specifications.

Any element from Table 10.3: Spectral Elements for use with ACS/WFC Configuration

DEUTERIUM


An exposure taken with the deuterium flat-field lamp. Permitted only with the ACS/SBC in ACCUM mode. The exposure time should normally not exceed 1000 seconds.

The following restrictions apply to subarray DEUTERIUM exposures:

Special requirements POS TARG and PATTERN may not be specified and Optional Parameters CENTERAXIS1 and CENTERAXIS2 may not have the value TARGET. STScI will not support such specifications.

Any element from tables 10.3: Spectral Elements for use with ACS/WFC Configuration or 10.7: Spectral Elements for use with ACS/SBC Configuration

DARK

Required target for ALIGN and ANNEAL modes

None

3 Use of Optional Parameters with internal targets:

No Optional Parameters are permitted with ACS/SBC

All  internal  target  exposures  will  be  taken  as  single  exposures  (i.e., an implicit CR-SPLIT=NO).

Optional Parameters permitted with BIAS are: GAIN; COMPRESSION; AMP; SIZEAXIS2; SIZEAXIS1; CENTERAXIS2; CENTERAXIS1; READTYPE; SPEED.

Optional Parameters permitted with DARK and TUNGSTEN are: GAIN; COMPRESSION; FLASH; FLASHCUR; FLASHEXP; AMP; CTE; SIZEAXIS1; SIZEAXIS2; CENTERAXIS1; CENTERAXIS2; READTYPE; SPEED

Optional Parameters permitted with DEUTERIUM are: None

4 DEF means the spectral element currently in place for the ACS/WFC, and means an opaque position for the ACS/SBC. For ACS/WFC Target Name BIAS, the spectral elements are predefined by the STScI ACS Instrument team.

Expand/Collapse all...


Related Links

10.2 ACS Wide Field Channel, WFC
10.3 ACS Solar Blind Channel, SBC
10.4 ACS Restricted Engineering Modes
10.5 ACS Reference Information




Table of Contents


Change Log

Version Cycle 26 October 2018

  1. PR.90827 2018 ACS Proposal Instructions - New Aperture SBC-LODARK
    10.1 Introduction to ACS

Initial Conversion HST Cycle 25 Phase II Proposal Instructions (Engineering) Version Cycle 25 (June 2018)