### 1 Introduction

Echelle spectrographs are available as common-user instruments at several observatories and satellites. These spectrographs offer the observer both a reasonably high resolution and a wide wavelength-coverage; at the expense of a fairly complex data-reduction procedure.

This document is intended as an introductory guide for observers new to échelle work. Experienced observers may wish to consult §5 for outline information on the main packages available for échelle data reduction.

#### 1.1 Other Sources of Information

This Guide complements the Starlink Echelle Data Reduction Cookbook (Starlink document SC/3) which contains examples of data-reduction scripts, including templates for fully automated data reductions with ECHOMOP.

A significant part of the process of successful spectrum extraction is the preliminary handling of the CCD data frames. Those planning to use IRAF1 should consult A User’s Guide to CCD Reductions with IRAF (UGCRI) by Philip Massey. UGCRI is quite a good document for any user of CCD data, even those planning to use e.g. CCDPACK or FIGARO to do the preparation—the CCD Reduction Cookbook (SC/5) is the definitive introduction to this type of work.

IRAF users should look at the two documents for échelle data reduction within IRAF: A User’s Guide to Reducing Echelle Spectra With IRAF, and Guide to the Slit Spectra Reduction Task DOECSLIT. These give a comprehensive description of the IRAF approach to échelle data. There is also a hypertext tutorial for DOECSLIT at

You may be able to access a local copy of this tutorial; consult your system manager.

There is an excellent guide tailored to the reduction of échelle data taken using the Hamilton Spectrograph: Introduction to Echelle Data Reduction Using the Image Reduction Analysis Facility, which is a Lick Observatory Technical report. (A PostScript copy is available from the Starlink Echelle Support Pages.) This is a complete step-by-step run through of échelle data reduction using IRAF—from CCD data to calibrated spectra.

The primary documentation for ECHOMOP is in ECHOMOP—Echelle data reduction package (Starlink document SUN/152). This document explains each of the data-reduction steps using ECHOMOP and includes some general advice and tips. There is also additional information and advice in the on-line HELP for ECHOMOP if you get stuck.

An up-to-date set of hypertext documents for Starlink échelle data reduction and related information; including hypertext help, bug reports, comments and news, is maintained at

• http://www.star.ucl.ac.uk/~mjc/echelle/

Terms in the body text of this Guide in bold are described in the glossary later in this document; if you cannot find the term you want there, you might try the NASA Thesaurus:

• http://www.sti.nasa.gov/nasa-thesaurus.html

1IRAF documents can be found in your IRAF installation; you do not need to get them from Tucson or a mirror. Check with your manager for details.