Cosmic Origins Spectrograph Instrument Handbook for Cycle 17

1.1 Purpose

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This COS Instrument Handbook is meant to be the basic reference manual for the Cosmic Origins Spectrograph, and it describes COS' design, performance, operations, and calibration. This Handbook is written and maintained at STScI. We have attempted to incorporate the best available information, but as this is written COS is not yet installed in HST and therefore its performance parameters are inevitably based on data obtained during tests on the ground.

There are three occasions upon which a reader would consult this Handbook:

• To obtain the instrument-specific information needed to prepare a Phase I proposal for HST time;
• To obtain more detailed usage information when writing a Phase II program once a proposal has been accepted;
• To find the information about the performance and operation of COS to help in understanding and interpreting observations that have already been made.

This Handbook is not meant as a reference for COS data reduction or analysis; that is provided in a chapter in the HST Data Handbook.

1.1.1 Document conventions

This document follows the usual STScI conventions:

• Terms, words, or phrases which 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 as measured in vacuum and are in  Ångstroms (Å).

1.1.2 FEFU: Femto-erg Flux Unit

To simplify the text and to avoid typographical errors, particularly in exponents, in this Handbook we introduce and use a unit for fluxes: a FEFU, or "femto-erg flux unit."

 1 FEFU = 10-15 erg cm-2 sec-1 Å-1

This unit makes it possible to write most fluxes as integers. This convention also helps to reduce confusion from sometimes illegible exponents in figure legends.