### 1 Introduction

EXTRACTOR is a program for automatically detecting objects on an astronomical image and building a catalogue of their properties. It is particularly suited for the reduction of large scale galaxy-survey data, but also performs well on other astronomical images.

EXTRACTOR is Emmanuel Bertin’s SExtractor (Source-Extractor) program1 re-packaged for use in the Starlink Software Environment (see SG/4). This means that it uses the Starlink parameter system, accepts images in NDF format (see SUN/33) and uses the AST library (SUN/210) for astrometry.

A slightly modified version of SExtractor 2.19.5 is also included in the distribution of EXTRACTOR. You can find details of SExtractor’s operation, and how to configure it, in the SExtractor User’s Guide (which is issued as a Starlink Miscellaneous User Document, MUD 1652) – you configure EXTRACTOR in much the same way, although with some restrictions (see Section 6). The SExtractor home page – http://terapix.iap.fr/soft/sextractor – offers more information, such as a link to the SExtractor for Dummies.

In the Starlink release both EXTRACTOR and SExtractor do not offer the galaxy model fitting features that the full SExtractor builds do. This has been done to reduce the external package dependencies required, also it isn’t clear how useful these abilities would be without also creating an NDF version of PSFEx.

This document describes how to run EXTRACTOR, and includes instructions for running SExtractor from the Starlink distribution.

1BERTIN E. and ARNOUTS S., 1996, A&AS 117,393

2Note this document is still in draft, consequently you should read this in conjunction with the A&AS paper and the earlier SExtractor user document.