1.5 Purpose of this Handbook

This COS Instrument Handbook describes the design, performance, operation, and calibration of the Cosmic Origins Spectrograph. It is meant to be the principal reference manual for users of COS. This handbook is written and maintained at STScI. While it presents the best available information about COS at the time of the most recent update, tabulated parameters, such as dark rates or sensitivities, can evolve with time during a cycle.

The handbook is designed for readers who are:

• preparing a Phase I proposal to observe with HST,
• writing a Phase II program once a proposal has been accepted, or
• analyzing data from observations that have already been made.

This handbook is not meant to be the primary reference for COS data reduction or analysis. That information is provided in the COS Data Handbook. For quick reference, information on COS data products is provided in Chapter 11.

1.5.1 Document Conventions

This document follows the usual STScI conventions:

• Terms, words, or phrases that are to be entered by the user in a literal way in an HST proposal are shown in a typewriter or Courier font, such as "COS/FUV" or "TIME-TAG."
• Names of software packages or commands (such as CalCOS) are shown in boldface.

Wavelengths in this handbook, and in COS data products, are always measured in vacuum and are quoted in Angstroms (Å).