COS Instrument Handbook for Cycle 24

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Table of Contents

Cosmic Origins SpectrographInstrument Handbook for Cycle 24

Table of Contents

Acknowledgments

References and Additional Information

Chapter 1: An Introduction to COS

1.1 Overview

1.2 Observing with COS

1.2.1 Target Acquisitions

1.2.2 Observing Modes: Spectroscopic and Imaging

1.2.3 Observing Modes: TIME-TAG and ACCUM

1.2.4 Typical Observing Sequences

1.3 COS Quick Reference Guide

1.4 COS FAQ

1.5 Purpose of this Handbook

1.5.1 Document Conventions

Chapter 2: Special Considerations for Cycle 24

2.1 COS FUV Detector Lifetime Positions

2.2 COS Observations Below 1150 å: Resolution and Wavelength Calibration Issues

2.3 Time-Dependent Sensitivity Changes

2.4 Spectroscopic Use of the Bright Object Aperture

2.5 Non-Optimal Observing Scenarios

2.6 SNAP, TOO, and Unpredictable Source Programs with COS

2.7 Should I Use COS or STIS?

Chapter 3: Description and Performance of the COS Optics

3.1 The Optical Design of COS

3.1.1 External Shutter

3.1.2 The Apertures and Aperture Mechanism

3.1.3 Gratings and Mirrors: The Optics Select Mechanisms

3.2 Size of a Resolution Element

3.3 The COS Line-Spread Function

3.3.1 Non-Gaussianity of the COS LSF

3.3.2 Quantifying the Resolution

3.3.3 Impact on Equivalent Width Measurements

3.3.4 Extended Wings of the COS LSF

3.3.5 Enclosed Energy of COS LSF

Chapter 4: Description and Performance of the COS Detectors

4.1 The FUV XDL Detector

4.1.1 XDL Properties

4.1.2 XDL Spectrum Response

4.1.3 XDL Dark Rate

4.1.4 XDL Read-out Format

4.1.5 Non-linear Photon Counting Effects (Dead Time)

4.1.6 Stim Pulses

4.1.7 Pulse-height Distributions

4.1.8 Spatial Variation of the Dark Rate

4.2 The NUV MAMA Detector

4.2.1 MAMA Properties

4.2.2 MAMA Spectrum Response

4.2.3 MAMA Dark Rate

4.2.4 MAMA Read-Out Format

4.2.5 MAMA Dead Time

4.2.6 Non-Gaussian Wings in the MAMA PSF

Chapter 5: Spectroscopy with COS

5.1 The Capabilities of COS

5.1.1 First-Order Sensitivity

5.1.2 Sensitivity below 1150 å

5.1.3 Second-Order Sensitivity

5.1.4 Spectroscopic Resolving Power

5.1.5 Time-Dependent Sensitivity Changes

5.1.6 Dip in Sensitivity around 1180 å

5.1.7 Zero-Order Image

5.1.8 Internal Scattered Light

5.1.9 Spatial Resolution and Field of View

5.1.10 Photometric (Flux) Precision

5.1.11 Wavelength Accuracy

5.1.12 Vignetting of the NUV Channel

5.2 TIME-TAG vs. ACCUM Mode

5.2.1 TIME-TAG Mode

5.2.2 ACCUM Mode

5.3 Valid Exposure Times

5.4 Estimating the BUFFER-TIME in TIME-TAG Mode

5.4.1 BUFFER-TIME > 110 s and BUFFER-TIME > Exposure Time

5.4.2 BUFFER-TIME > 110 s and BUFFER-TIME ≤ Exposure Time

5.4.3 80 s < BUFFER-TIME ≤ 110 s)

5.4.4 BUFFER-TIME ≤ 80 s

5.4.5 BUFFER-TIME and AUTO-ADJUST

5.5 Spanning the Gap with Multiple CENWAVE Settings

5.6 FUV Single-Segment Observations

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 GO Wavecals (User-Specified)

5.7.4 No-Cal Wavecals

5.7.5 Inserting Wavecals in Observations with G130M/1055 and G130M/1096, SEGMENT=B

5.8 Fixed-Pattern Noise

5.8.1 COS Flat Fielding

5.8.2 Use of Multiple FP-POS Settings

5.9 COS Spectroscopy of Extended Sources

5.10 Wavelength Settings and Ranges

Chapter 6: Imaging with COS

6.1 Introduction to COS Imaging

6.2 Sensitivity

6.3 Image Characteristics

Chapter 7: Exposure-Time Calculator (ETC)

7.1 The COS Exposure Time Calculators

7.2 Imaging Observations of Red Objects

7.3 Sensitivity, Count Rate, and S/N

7.4 Detector and Sky Backgrounds

7.4.1 Detector Dark Count

7.4.2 Earthshine

7.4.3 Zodiacal Light

7.4.4 Airglow Emission

7.4.5 Tabular Sky Backgrounds

7.5 Extinction Correction

7.6 Examples

7.6.1 A Flat-Spectrum Source

7.6.2 An Early-Type Star

7.6.3 A Solar-Type Star with an Emission Line

7.6.4 A Faint QSO

Chapter 8: Target Acquisitions

8.1 Introduction

8.2 Target Acquisition Overview

8.3 ACQ/SEARCH Acquisition Mode

8.4 ACQ/IMAGE Acquisition Mode

8.5 ACQ/PEAKXD Acquisition Mode

8.5.1 Description

8.5.2 Effects of FUV Detector Y Walk

8.6 ACQ/PEAKD Acquisition Mode

8.7 Exposure Times

8.7.1 Imaging Acquisitions

8.7.2 Dispersed-Light Acquisitions

8.8 Centering Accuracy and Data Quality

8.8.1 Centering Accuracy and Wavelength Accuracy

8.8.2 Centering Accuracy and Photometric Precision

8.8.3 Centering Accuracy and Spectroscopic Resolution

8.9 Recommended Parameters for all COS TA Modes

8.10 Special Cases

8.10.1 Early Acquisitions and Preliminary Images

8.10.2 Extended or Multiple Targets

8.10.3 Offset Target Acquisitions

8.10.4 Acquisition Failure Actions and Diagnostics

Chapter 9: Scheduling Observations

9.1 Introduction

9.1.1 Phase I Proposal

9.1.2 Phase II Proposal

9.2 Generic Observatory Overheads

9.3 Spectral Element Movement Overheads

9.4 Acquisition Overheads

9.5 Science Exposure Overheads

9.6 First Exposure Overhead Adjustment

9.7 Examples of Orbit Estimates

9.7.1 Target Acquisition Using ACQ/IMAGE

9.7.2 ACQ/SEARCH plus ACQ/IMAGE Acquisition

9.7.3 FUV Acquisition plus TIME-TAG

9.7.4 FUV TIME-TAG with BOA and Multiple FP-POS

9.7.5 FUV TIME-TAG with Modified BUFFER-TIME

9.7.6 Single CENWAVE Example for Non-CVZ Targets using 4 FP-POS in 1 Orbit

9.7.7 Single CENWAVE Example for Non-CVZ Targets with 4 FP-POS in 2 Orbits

Chapter 10: Bright-Object Protection

10.1 Introduction

10.2 Screening Limits

10.3 Screening versus Data-Rate Limits

10.4 Source V Magnitude Limits

10.5 Tools for Bright-Object Screening

10.5.1 The Bright Object Tool (BOT)

10.5.2 The Exposure Time Calculator (ETC)

10.6 Policies and Procedures

10.7 On-Orbit Protection Procedures

Chapter 11: Data Products and Data Reduction

11.1 Overview

11.2 COS Data Files

11.3 Additional COS Files

Chapter 12: The COS Calibration Program

12.1 Introduction

12.2 Ground Testing and Calibration

12.3 SMOV4 Testing and Calibration

12.4 COS Monitoring Programs

12.5 Cycle 17 Calibration Program

12.6 Cycle 18 Calibration Program

12.7 Cycle 19 Calibration Program

12.8 Cycle 20 Calibration Program

12.9 Cycle 21 Calibration Program

12.10 Cycle 22 Calibration Program

12.11 Cycle 23 Calibration Program

Chapter 13: Spectroscopic Reference Material

13.1 Introduction

13.2 Using the Information in this Chapter

13.2.1 Grating Parameters

13.2.2 Wavelength Ranges

13.2.3 Grating Sensitivities and Effective Areas

13.2.4 Signal-to-Noise Plots

13.3 Gratings

FUV Grating G130M

FUV Grating G130M with CENWAVE=1222

FUV Grating G130M with CENWAVE=1055 or 1096

FUV Grating G160M

FUV Grating G140L

NUV Grating G185M

NUV Grating G225M

NUV Grating G285M

NUV Grating G230L

13.4 Spectrograph Design Parameters

13.4.1 FUV Channel

13.4.2 NUV Gratings

13.5 The Location of COS in the HST Focal Plane

13.6 The COS User Coordinate System

Glossary

A Glossary of Terms and Abbreviations