Advanced Camera for Surveys Instrument Handbook for Cycle 14

Chapter 1:
Introduction

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1.1 Purpose
    1.1.1 Document Conventions
    1.1.2 Examples Used in this Handbook
1.2 Handbook Layout
1.3 Preparing an Observing Proposal with ACS
1.4 The Help Desk at STScI
1.5 The ACS Web Site and Supporting Information

The Advanced Camera for Surveys (ACS) is a third-generation instrument that was installed in the Hubble Space Telescope during Servicing Mission 3B, March 7, 2002. Its primary purpose is to increase the discovery efficiency of imaging with HST by providing a combination of detector area and quantum efficiency that surpasses that available from previous instruments by a factor of 10 or so. It consists of three independent cameras that provide wide-field, high resolution and ultraviolet imaging capability respectively, with a broad assortment of filters designed to address a large range of scientific goals. Additional coronagraphic, polarimetric and grism capabilities make this a versatile and powerful instrument. This Instrument Handbook provides instrument-specific information you will need to propose for ACS observations (Phase I), design accepted programs (Phase II), and understand ACS in detail. The companion ACS Data Handbook describes how to deal with ACS data once it has been obtained.

This Chapter explains the layout of the present Handbook and describes how to use the Help Desk at STScI and the STScI ACS World Wide Web pages to get help and further information. Instrument and operating updates will be posted on the ACS Web pages.

1.1 Purpose

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The ACS Instrument Handbook is the basic reference manual for the Advanced Camera for Surveys, and describes the instrument's properties, performance, operations and calibration. The Handbook is maintained by scientists at STScI. Additional information has been provided by the Investigation Definition Team, led by Dr. Holland Ford of Johns Hopkins University, and by the principal contractors, Ball Aerospace.

We have designed the document to serve three purposes:

• To provide instrument-specific information for preparing Cycle 14 Phase I observing proposals using ACS.
• To provide instrument-specific information to support the design of Phase II proposals for accepted ACS programs, in conjunction with the Phase II Proposal Instructions.
• To provide technical information about the operation and expected performance of the instrument, which can help in the understanding of problems and in the interpretation of data acquired with ACS.

1.1.1 Document Conventions

This document follows the usual STScI convention in which terms, words and phrases which are to be entered by the user in a literal way on an HST proposal are shown in a typewriter font (e.g., ACS/WFC, F814W). Names of software packages or commands are given in bold type (e.g., calacs).

Wavelength units in this Handbook are in Angstroms (Å), and fluxes are generally given in erg cm^-2s^-1Å^-1.

1.1.2 Examples Used in this Handbook

To illustrate the use of ACS, we have devised a set of representative programs that cover a range of its capabilities. We hope that they will prove helpful to users both in determining the capabilities of the instrument and in writing a proposal to request HST time. The examples are:

1. Wide Field Channel imaging of a faint point source.
2. Solar Blind Channel (SBC) prism spectroscopy of a faint standard star.
3. Polarimetry of the jet of M87.
4. SBC imaging of Jupiter's aurora.
5. Coronagraphy of the circumstellar disk of Pic.

1.2 Handbook Layout

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To guide you through ACS's capabilities and help optimize your scientific use of the instrument we have divided this handbook into four parts:

• Part I - Introduction
• Part II - User's Guide
• Part III - Supporting Material
• Part IV - Calibration

Figure 1.1 provides a roadmap to navigating this Handbook.

Figure 1.1: ACS Handbook Roadmap for Proposal Preparation


 

The chapters of this Handbook are as follows:

• Part I - Introduction
  • Chapter 1 - Introduction, includes information about getting help.
  • Chapter 2 - Special Considerations for Cycle 14, describes special policy considerations for using ACS during Cycle 14.
• Part II - User's Guide
  • Chapter 3 - Introduction to ACS, provides an introduction to ACS's capabilities. A discussion is provided to help guide you through the technical details you need to consider in choosing the optimum ACS configuration and in determining the number of orbits to request.
  • Chapter 4 - Imaging, provides a description of ACS's imaging capabilities, including camera resolutions and sensitivities.
  • Chapter 5 - Polarimetry, Coronagraphy and Prism/Grism Spectroscopy, provides detailed information on these specialized observation modes.
  • Chapter 6 - Exposure Time Calculations, describes how to perform signal-to-noise calculations, either by using pencil and paper, or by using software tools that are provided on the World Wide Web.
  • Chapter 7 - Feasibility and Detector Performance, provides a description of the three detectors and their physical characteristics, capabilities and limitations, including saturation, linearity and bright object limits.
  • Chapter 8 - Observing Techniques, describes some methods that can be used to obtain the best science from ACS, including dithering and the use of pre-defined patterns that mitigate the effects of detector imperfections.
  • Chapter 9 - Overheads and Orbit Time Determination, provides information to convert from a series of planned science exposures to an estimate of the number of orbits, including spacecraft and ACS overheads. This chapter applies principally to the planning of Phase I proposals.
• Part III - Supporting Material
  • Chapter 10 - Imaging Reference Material, provides summary information and filter transmission curves for each imaging filter.
• Part IV - Calibration
  • Chapter 11 - Pipeline Calibration, briefly describes the processing of ACS data by the STScI pipeline and the products that are sent to observers.
  • Chapter 12 - Expected Calibration Accuracies, summarizes the accuracies expected for ACS data calibrated by the STScI pipeline.
  • Chapter 13 - Calibration Plans, provides an overview of the current state of ACS calibration, including changes resulting from the Servicing Mission Observatory Verification (SMOV) and Cycle 11 and 12 calibration programs and plans for Cycle 13 and 14 calibration.

1.3 Preparing an Observing Proposal with ACS

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Use the ACS Instrument Handbook together with the Hubble Space Telescope Call for Proposals for Cycle 14 (CP) when assembling your ACS Phase I proposal. In addition the HST Primer provides a basic introduction to the technical aspects of HST and its instruments, and explains how to calculate the appropriate number of orbits for your Phase I observing time requests. The CP provides policies and instructions for proposing; the ACS Instrument Handbook contains detailed technical information about ACS, describing its expected performance, and presenting suggestions for use. The next Chapter in the Handbook describes special considerations for Cycle 14.

If your Phase I proposal is accepted, you will be asked to submit a Phase II proposal in which you specify the exact configurations, exposure times and sequences of observations that ACS and the telescope should perform. To assemble your Phase II proposal, you should use the ACS Instrument Handbook in conjunction with the Phase II Proposal Instructions. The Instructions describe the exact rules and syntax that apply to the planning and scheduling of ACS observations and provide relevant observatory information.

1.4 The Help Desk at STScI

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STScI maintains a Help Desk, the staff of which quickly provide answers on any HST-related topic, including questions regarding ACS and the proposal process. The Help Desk staff have access to all of the scientists and resources available at the Institute, and they maintain a database of answers so that frequently asked questions can be immediately answered. The Help Desk staff also provide STScI documentation, in either hardcopy or electronic form, including Instrument Science Reports and Instrument Handbooks. Questions sent to the Help Desk are answered within two working days. Usually, the Help Desk staff will reply with the answer to a question, but occasionally they will need more time to investigate the answer. In these cases, they will reply with an estimate of the time needed to reply with the full answer.

We ask that you please send all initial inquiries to the Help Desk. If your question requires an ACS Instrument Scientist to answer it, the Help Desk staff will put one in contact with you. By sending your request to the Help Desk, you are guaranteed that someone will provide you a timely response.

To contact the Help Desk at STScI:

• Send E-mail: help@stsci.edu (preferred)
• Phone: 1-410-338-1082
  Toll-free in the U.S.: 1-800-544-8125

The Space Telescope European Coordinating Facility (ST-ECF) also maintains a Help Desk. European users should generally contact the (ST-ECF) for help; all other users should contact STScI. To contact the ST-ECF Help Desk:

• Send E-mail: stdesk@eso.org

1.5 The ACS Web Site and Supporting Information

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The ACS Branch at STScI maintains a World Wide Web (WWW) site, as part of STScI's web service. The address for the STScI ACS page is:

 http://www.stsci.edu/hst/acs

The STScI ACS pages include sections that fall into the following categories:

• Late Breaking News: This is where new and important information is posted.
• Document Archive: Electronic versions of this Handbook will be maintained on the WWW site. In addition, more detailed technical information concerning the development, performance, testing, operation and calibration of ACS are contained in a series of ACS Instrument Science Reports (ISRs) and STScI Analysis Newsletters (STANs). These reports can be downloaded from the WWW pages or paper copies can be requested from the Help Desk.
• Software Tools: This section includes the Exposure Time Calculator (ETC), which can be used to predict exposure times for ACS observations.
• Data Analysis: Includes links to the locations of reference files and the CALACS tutorial.
• Performance: Information on the status of ACS and discussion of calibration strategies.
• FAQs: This section contains answers to the most Frequently Asked Questions.
• Help: This section tells you whom to contact when you need help.

Other information, not specific to ACS, can generally be accessed through the top-level STScI web page: http://www.stsci.edu/

	Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu