Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

Table of Contents

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Acknowledgments

Chapter 1: Introduction

1.1 Purpose of This Handbook

1.1.1 Document Conventions

1.1.2 FEFU: Femto-erg Flux Unit

1.2 Preparing Proposals and Observing with COS

1.2.1 The STScI Help Desk

1.2.2 COS Web Pages and Supporting Information

Chapter 2: Special Considerations for Cycle 17

2.1 SM4 and the Installation of COS

2.2 Observing Considerations for Cycle 17

2.2.1 The COS GTO Program

2.2.2 Survey and SNAP Programs with COS

2.2.3 Non-point Sources Uses of COS

2.2.4 Three-Gyro Observing with HST

2.3 Should I Use COS or STIS?

Chapter 3: A Tour Through COS

3.1 The Location of COS in the HST Focal Plane

3.2 The Optical Design of COS

3.2.1 External Shutter

3.2.2 The Apertures and Aperture Mechanism

3.2.3 Gratings and Mirrors: The Optics Select Mechanisms

3.2.4 Detectors

3.2.5 On-board Calibration Lamps

3.3 Basic Instrument Operations

3.3.1 Target Acquisitions

3.3.2 Data Taking: TIME-TAG and ACCUM

3.3.3 Wavelength Calibration

3.3.4 Typical Observing Sequences

3.3.5 Data Storage and Transfer

3.4 COS Illustrated

3.5 COS Quick Reference Guide

Chapter 4: Detector Performance

4.1 The FUV XDL

4.1.1 XDL Properties

4.1.2 XDL Spectrum Response

4.1.3 XDL Background Rates

4.1.4 XDL Read-out Format

4.1.5 ACCUM and TIME-TAG Modes

4.1.6 Stim Pulses

4.1.7 Pulse-height Distributions

4.1.8 FUV Detector Lifetime Sensitivity Adjustments

4.2 The NUV MAMA

4.2.1 MAMA Properties

4.2.2 MAMA Spectrum Response

4.2.3 MAMA Non-linearity

4.2.4 Detector Format

4.2.5 Pulse-height Distributions

4.2.6 Read-out Format, A-to-D Conversion, etc.

Chapter 5: Spectroscopy with COS

5.1 The Capabilities of COS

5.1.1 Signal-to-noise Considerations

5.1.2 Photometric (Flux) Precision

5.1.3 Spatial Resolution and Field of View

5.1.4 Wavelength Accuracy

5.1.5 Scattered Light in COS Spectra

5.1.6 Spectroscopic Resolving Power

5.1.7 Sensitivity

5.1.8 Sensitivity to second-order spectra

5.2 Non-linear Photon Counting Effects (Dead-time Correction)

5.3 Exposure Time Considerations

5.4 Apertures

5.5 TIME-TAG or ACCUM?

5.5.1 TIME-TAG Mode

5.5.2 ACCUM Mode

5.6 FUV Gap Coverage and Single Segment Usage

5.7 Internal Wavelength Calibration Exposures

5.7.1 Concurrent Wavelength Calibration with TAGFLASH

5.7.2 AUTO Wavecals (When TAGFLASH is not Used)

5.7.3 Wavelength Calibration Exposures with the BOA

5.7.4 User-specified Wavelength Calibration Exposures (GO Wavecals)

5.8 Achieving Higher Signal-to-noise using FP-POS

5.8.1 Use of Optional Parameter FP-POS

5.8.2 FUV Signal-to-noise

5.8.3 NUV Signal-to-noise

5.9 EXTENDED Optional Parameter

5.10 Calibrations

5.10.1 Internal Calibrations

5.10.2 External Calibrations

5.11 Wavelength Settings and Ranges

5.11.1 "Painting" a Complete NUV Spectrum

Chapter 6: NUV Imaging

6.1 Essential Facts About COS Imaging

6.2 Configurations and Imaging Quality

6.3 Sensitivity

6.4 Image Characteristics

Chapter 7: Target Acquisitions

7.1 The Need for Target Acquisition

7.2 Initial HST Pointing and Coordinate Accuracy

7.3 A Quick Guide to COS Acquisitions

7.4 Acquisition Effects on Data Quality

7.4.1 The HST PSF at the COS Aperture

7.4.2 Centering Accuracy and Photometric Precision

7.4.3 Centering Accuracy and the Wavelength Scale

7.4.4 Centering Accuracy and Spectroscopic Resolution

7.5 Imaging Acquisitions

7.5.1 Exposure Times and Count Rates

7.5.2 Imaging Acquisitions with Mediocre Coordinates

7.5.3 Imaging Acquisitions with MIRRORB or the BOA

7.6 FUV Dispersed-Light Acquisitions

7.6.1 FUV Dispersed-light Acquisition Summary

7.6.2 Mode=ACQ/SEARCH: The Spiral Target Search

7.6.3 PEAKXD: Peaking up in the Cross-dispersion Direction

7.6.4 PEAKD: Peaking up in the Along-dispersion Direction

7.7 NUV Dispersed-Light Acquisitions

7.8 Acquisition Techniques for Crowded Regions

7.9 Early Acquisitions and Preliminary Images

Chapter 8: Observing Strategy and Phase I

8.1 Designing a COS Observing Proposal

8.1.1 Identify the Science Requirements and COS Configuration

8.1.2 Use of Available-but-Unsupported Capabilities

8.1.3 Calculate Exposure Time and Assess Feasibility

8.1.4 Identify the Need for Additional Exposures

8.1.5 Estimating Data Volume

8.1.6 Determine Total Orbit Request

8.2 Bright Object Protection

8.3 Patterns and Dithering

8.4 A "Road Map" for Optimizing Observations

8.4.1 Get the Tools and Rules

8.4.2 Choose Instrument Configurations

8.5 Parallel Observations While Using COS

Chapter 9: Overheads and Orbit Usage Determination

9.1 Observing Overheads

9.2 Generic Observatory Overheads

9.3 Spectral Element Movement Overheads

9.4 Acquisition Overheads

9.5 Science Exposure Overheads

9.6 Examples of Orbit Estimates

9.6.1 FUV Acquisition plus FUV TIME-TAG

9.6.2 NUV TIME-TAG

9.6.3 NUV plus FUV TIME-TAG

9.6.4 FUV TIME-TAG with BOA and FLASH=NO

9.6.5 FP-POS=AUTO with FUV TIME-TAG and FLASH=YES

Chapter 10: Exposure-Time Calculator (ETC)

10.1 The COS Exposure Time Calculators

10.2 Count Rate, Sensitivity, and S/N

10.2.1 Centering Accuracy and Photometric Precision

10.3 Detector and Sky Backgrounds

10.3.1 Detector dark background

10.3.2 Earthshine

10.3.3 Zodiacal Light

10.3.4 Geocoronal Airglow Emission

10.4 Extinction Correction

10.5 Tabular Sky Backgrounds

10.6 Examples

10.6.1 A Flat-spectrum Source

10.6.2 An Early-type Star

10.6.3 A Solar-type Star with an Emission Line

10.6.4 A Faint QSO

Chapter 11: COS in Phase II

11.1 Essential Program Information

11.2 A "Roadmap" for Phase II Program Preparation

11.3 Get the Tools and Rules

11.4 Specify Instrument Usage Particulars

11.4.1 Gather Essential Target Information

11.4.2 Assess Target Acquisition Strategies

11.4.3 Determine the Science Exposure Needs

11.5 Safety First: Bright Object Protection

11.5.1 Limiting Magnitudes and Bright Object Limits

11.5.2 Bright Object Protection Procedures

11.6 Recap of COS Optional Parameters

Chapter 12: Data Products and Data Reduction

12.1 FUV TIME-TAG Data

12.1.1 Raw FUV TIME-TAG Data

12.1.2 Corrected FUV TIME-TAG Data

12.1.3 Corrected FUV TIME-TAG Image

12.1.4 FUV TIME-TAG Error Array

12.1.5 FUV TIME-TAG Science Spectrum

12.2 NUV TIME-TAG Data

12.2.1 Raw NUV TIME-TAG Data

12.2.2 Corrected NUV TIME-TAG Data

12.2.3 Corrected NUV TIME-TAG Image

12.2.4 NUV TIME-TAG Error Array

12.2.5 NUV TIME-TAG Science Spectrum

12.3 FUV ACCUM Data

12.3.1 Raw FUV ACCUM Data

12.3.2 Corrected FUV ACCUM Data

12.3.3 FUV ACCUM Error Array

12.3.4 FUV ACCUM Science Spectrum

12.4 NUV ACCUM Data

12.5 NUV ACQ/IMAGE Data

12.5.1 Raw NUV ACQ/IMAGE Data

12.5.2 Corrected NUV ACQ/IMAGE Image

12.6 COS Output files and Naming Conventions

12.6.1 General Rules

12.6.2 Spectroscopy

12.6.3 Imaging:

12.6.4 Target acquisition:

Chapter 13: Reference Material

13.1 Apertures

13.1.1 The Aperture Mechanism (ApM)

13.1.2 Primary Science Aperture

13.1.3 Bright Object Aperture

13.1.4 PSA/BOA "Cross-talk"

13.1.5 Wavelength Calibration Aperture

13.1.6 Flat-field Calibration Aperture

13.2 COS Mechanisms

13.2.1 Optics Select Mechanism 1 (OSM1)

13.2.2 Optics Select Mechanism 2 (OSM2)

13.2.3 External Shutter

13.3 COS Optical Elements

13.3.1 FUV Gratings

13.3.2 NUV Gratings

13.3.3 Mirrors

13.4 Modeling of the HST PSF at the COS Aperture

13.4.1 Optical Modeling Procedure

13.4.2 PSF Model Results

13.5 Details of TAGFLASH Execution

13.5.1 Detailed Definitions and Rules for Lamp Flash Sequences

13.5.2 TAGFLASH Exposure Parameters

Glossary

Index