1.2 Introduction to the Handbook

The STIS Instrument Handbook is the basic reference manual for the Space Telescope Imaging Spectrograph (STIS); it describes the instrument’s properties, performance, operations, and calibration. The Handbook is maintained by the STIS team at STScI. Wherever possible, the most recent operational data have been incorporated into this revised edition. 
We have designed the document to serve three purposes:

• To provide instrument-specific information for preparing Phase I STIS observing proposals.
• To provide instrument-specific information to support the design of Phase II proposals for accepted STIS programs.
  
• To provide technical information about the performance and operation of the instrument that can help in the understanding of problems and in the interpretation of data acquired with STIS. 

This Handbook is not meant to serve as a manual for the reduction and analysis of data taken with STIS. The STIS Data Handbook (also available from the STIS website or the HST Documentation website) describes how to work with STIS data.

1.2.1  Document Conventions

This document follows the usual STScI convention in which terms, words, and phrases which are to be entered by the user in a literal way on an HST proposal are shown in a typewriter font (e.g., STIS/CCD, SHADOW). Names of software packages or commands (e.g., calstis) are given in boldface. 

Wavelengths in this Handbook and in STIS data products are always measured in vacuum conditions. Wavelength units in this Handbook are in Angstroms (Å).

1.2.2  Examples Used in this Handbook

The Handbook uses six observational examples to illustrate various scenarios such as calculation of exposure times, estimation of overheads, etc. throughout the text. The examples are:

• Long-slit optical spectroscopy of the nearby galaxy NGC 4406 (M86). 
• Long-slit optical and UV spectroscopy and optical imaging of NGC 6543, the Cat's Eye planetary nebula. 
  
• First-order low-resolution spectroscopy covering STIS' full wavelength range from 1150 Å in the UV to 10,300 Å in the near-infrared (NIR) of the solar analog star P041-C, in the continuous viewing zone (CVZ). 
  
• Echelle spectroscopy of the O-type star Sk-69°215 in the Large Magellanic Cloud (LMC), a target in the CVZ. 
  
• Deep optical imaging of a random field. 
  
• Time-resolved UV spectroscopy of the flare star AU Mic. 

In addition, we use stellar spectra throughout the Handbook to illustrate signal-to-noise ratio calculations and derive limiting magnitudes. Figure 1.1 shows the normalized spectra of O, A, G, and M stars from an observed catalog of stars (for details, see Buser, 1978, A&A, 62, 411) which are used in the Handbook examples. 

Many of the performance characteristics of STIS change over time. These changes include gradual decreases in optical throughput, increases in detector dark currents, and decreasing charge transfer efficiencies. Most of the figures and tables illustrating throughputs, signal-to-noise calculations, bright object limits, and limiting magnitudes had been recalculated for the Cycle 17 version of this Handbook based on the best available performance estimates for Cycle 17. Except where otherwise noted these tables and figures have not been updated for the additional changes expected for Cycle 33. In most cases the differences will be modest. For more up-to-date performance estimates, it is suggested that users consult the Performance section of the STIS web pages and the STIS ETCs (Exposure Time Calculators; available at http://etc.stsci.edu/).  The sensitivities and other instrument parameters adopted for use with the Cycle 33 ETCs are our best estimates for April 2025 (i.e., mid-Cycle 32).

The software tools used to process, inspect, and analyze STIS data have also evolved over time.  In particular, the IRAF/STSDAS routines originally used for analyses of STIS (and other HST) data are no longer supported by STScI, and they have been largely replaced by python-based tools performing the same (or very similar) functions (see, e.g., the stistools package).  While most of the software references in this Handbook now are to the newer python-based tools/routines, a few references still remain to some of the IRAF/STSDAS routines, particularly where no exact replacement has been established.