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 basically Emmanuel Bertin's SExtractor (Source-Extractor) program¹ re-packaged for use in the Starlink Software Environment . This means that it uses the Starlink parameter system, accepts images in NDF format and uses the AST library for astrometry.

Extending the program to use NDFs allows it to read and write other image formats using the NDF library `on-the-fly' conversion facility . Conversion to and from many ``standard'' astronomical formats are available by using the CONVERT package - these include FITS and IRAF OIF.

A slightly modified version of SExtractor 2.5.0 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 . The SExtractor home page - http://terapix.iap.fr/soft/sextractor - offers more information, such as a link to the SExtractor for Dummies.

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