Space Telescope Science Institute
COS Instrument Handbook
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Table of Contents

Cosmic Origins SpectrographInstrument Handbookfor Cycle 22
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 22
2.1 COS FUV Detector Lifetime Position
2.2 COS Observations Below 1150 : Resolution and Wavelength Calibration Issues
2.3 Time-Dependent Sensitivity Changes
2.4 Non-Optimal Observing Scenarios
2.5 SNAP and TOO Programs with COS
2.6 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
Primary Science Aperture
Wavelength Calibration Aperture
Bright Object Aperture
Flat-Field Calibration Aperture
3.1.3 Gratings and Mirrors: The Optics Select Mechanisms
FUV Channel Optical Design
OSM2 and the NUV Channel
Imaging with the NUV Mirror
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
Gain Sag
Detector Walk
Mitigation Strategies
Calcos Changes
Onboard Changes
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
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
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
Doppler Correction for TIME-TAG Mode
Pulse-Height Data for TIME-TAG
5.2.2 ACCUM Mode
Observing Efficiencies with ACCUM
Doppler Correction for ACCUM Mode
Pulse-Height Distribution Data for ACCUM Mode Observations
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
Requirements for 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
Bright-Object Protection
8.2 Target Acquisition Overview
Please Note...
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
FUV Bright Object Protection
NUV Bright Object Protection
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 Plans
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

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