Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

Table of Contents

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Table of Contents

Acknowledgments

Chapter 1: Introduction

1.1 Purpose

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 Spectrographs Branch and COS Team

1.2.2 The STScI Help Desk

1.2.3 COS web pages and supporting information

1.2.4 Non-proprietary COS data

Chapter 2: Special Considerations for Cycle 17

2.1 SM4 and the Installation of COS

2.2 Knowledge of Instrument Performance

2.3 SMOV

2.4 The Availability of COS During Cycle 17

2.5 Limitations on Proposing to Use COS

2.5.1 The COS GTO program

2.5.2 SNAPshots with COS

2.5.3 Non-point sources uses of COS

2.6 Should I Use STIS instead of COS?

Chapter 3: A Tour through COS

3.1 COS' Location in the HST Focal Plane

3.2 COS' Capabilities

3.2.1 Signal-to-noise considerations

3.2.2 Photometric (flux) precision

3.2.3 Wavelength accuracy

3.2.4 Sensitivity

3.2.5 Non-linear photon counting effects (dead-time correction)

3.3 The Design of COS

3.3.1 Optical Configuration

3.3.2 Apertures

3.3.3 The FUV and NUV Channels

3.3.4 Detectors

3.3.5 On-board Calibration Lamps

3.3.6 Mechanisms

3.4 Basic Instrument Operations

3.4.1 Target acquisitions

3.4.2 TIME-TAG and ACCUM

3.4.3 Wavelength calibration

3.4.4 Typical observing sequences

3.4.5 Data storage and transfer

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 read-out format

4.1.4 Analog-to-digital conversion

4.1.5 Stim pulses (e-stims)

4.1.6 Pulse-height distributions

4.1.7 FUV detector lifetime adjustments

4.2 The NUV MAMA

4.2.1 MAMA properties

4.2.2 MAMA spectral response

4.2.3 MAMA non-linearity

4.2.4 Detector format

4.2.5 Read-out format, A-to-D conversion, etc.

Chapter 5: Spectroscopy with COS

5.1 Configurations and Optical Elements

5.2 Exposure Time Considerations

5.3 Apertures

5.4 TIME-TAG or ACCUM?

5.4.1 TIME-TAG mode

5.4.2 ACCUM mode

5.5 FUV gap coverage and single segment usage

5.6 Internal Wavelength Calibration Exposures

5.6.1 What "TAGFLASH" does during TIME-TAG observations

5.6.2 AUTO wavecals (when "Tagflash" is not used)

5.6.3 User-specified wavelength calibration exposures (GO wavecals)

5.7 Achieving Higher Signal-to-noise

5.8 EXTENDED

5.9 Calibrations

5.9.1 Internal calibrations

5.10 FUV Wavelength Settings And Ranges

Chapter 6: NUV Imaging

6.1 Summary

6.2 Configurations and Optical Elements

6.3 Exposure Time Considerations

6.4 TIME-TAG or ACCUM?

6.5 Attenuation Considerations

6.6 Extended Objects

6.7 Image Characteristics

Chapter 7: Target Acquisitions

7.1 Planning a COS Acquisition

7.2 Safety First: Bright Object Protection

7.2.1 FUV bright object protection

7.2.2 NUV bright object protection

7.2.3 Screening limits

7.2.4 Risks from nearby objects

7.3 How Accurate an Acquisition Do I Need?

7.3.1 Centering accuracy and photometric precision

7.3.2 Centering accuracy and the wavelength scale

7.3.3 Centering accuracy and spectroscopic resolution

7.4 COS Acquisitions and Coordinate Accuracy

7.5 Imaging Acquisitions

7.5.1 Exposure times and count rates

7.5.2 Imaging acquisitions with mediocre coordinates

7.6 FUV Dispersed-Light Acquisitions

7.6.1 FUV dispersed-light acquisition summary

7.6.2 Mode=ACQ: 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

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

8.2.1 Limiting magnitudes and bright object limits

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 Summary

9.2 Generic Observatory Overhead

9.3 Spectral Element Movement Overheads

9.4 Acquisition Overheads

9.5 Science Exposure Overheads

9.6 Examples of Orbit Estimates

9.6.1 Example 1: NUV TIME-TAG

9.6.2 Example 2: NUV plus FUV TIME-TAG

9.6.3 Example 3: FUV Acquisition plus FUV TIME-TAG

9.6.4 FUV TIME-TAG with BOA and FLASH=NO

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

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 Recap of COS Optional Parameters

Chapter 12: Data Products and Data Reduction

12.1 COS Data Products

12.1.1 FUV TIME-TAG data

12.1.2 NUV TIME-TAG data

12.1.3 FUV ACCUM data

12.1.4 NUV ACCUM data

12.1.5 NUV ACQ/IMAGE data

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 Wavelength Calibration Aperture

13.1.5 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

Glossary