Introduction

This document is an introduction to the IRAF (Image Reduction and Analysis Facility) software package and its use on Starlink systems. It is aimed at people who are considering whether or not to use IRAF or who are using it for the first time.

IRAF is a powerful and comprehensive environment for reducing and analysing astronomical data. It was developed at the National Optical Astronomy Observatories (NOAO), Tucson and is now in widespread use around the world. IRAF has its own data file format, command language, on-line help system and programming language. It is a modular system. The basic core, which is always present, provides general facilities for image processing and data reduction. For more specialised tasks additional packages are loaded to augment the core system. Software for processing most sorts of astronomical data is available for the IRAF environment. IRAF is available on all the variants of Unix currently supported by Starlink: Digital Alpha/Digital Unix, SUN/Solaris and PC/Linux.

IRAF is one of several major software environments which are available to Starlink users and upon which entire data-analysis campaigns can be based. Some other examples include: Starlink's own large collection of utilities and application packages, the various incarnations of the Figaro package (SUN/86[14]), AIPS (SUN/207[12]) and MIDAS. Each package has its own particular strengths and special capabilities; IRAF, AIPS and Figaro are probably the most extensive.

IRAF is a sound choice for many Starlink data-analysis users, especially where compatibility with overseas collaborators is a requirement. The choice is harder for those wishing to develop major applications of their own, who may be reluctant to adopt IRAF's non-standard programming language, SPP, or who feel that the `flat' IRAF data format is inadequate for their purposes (see Section  for further details). Those who need formal guarantees of future support should also be very wary about committing themselves to any package which is not under UK control. However, IRAF is an important weapon in the armoury of the average Starlink data-analysis user and likely to remain so for some years.

The structure of this document is:

Part I

- an overview of IRAF,

Part II

- some simple worked examples.

We suggest that you read through the overview to gain an impression of what IRAF is about and then try some of the worked examples. If you have a particular aversion to reading manuals you could proceed straight to the worked examples, though we do not recommend this.

The presence of IRAF is not mandatory at Starlink sites, though in practice it is available at most sites. You should check the arrangements at your site with your local site manager. If IRAF is not available at your site it is possible to obtain a copy via the Internet; the following section gives the details.