7 Introduction

This part of the cookbook provides a set of detailed recipes for performing some simple tasks with GAIA. The topics covered are:

• displaying an image (Section 8),
• retrieving remote images and catalogues via the Internet (Section 9),
• using World Coordinates (Section 10),
• superimposing and contouring images (Section 11),
• astrometric calibration of an image (Section 12),
• automatic object detection (Section 13),
• measuring instrumental magnitudes (Section 14).

Strictly speaking these recipes can be read in any order, and you can simply turn to the ones that seem most relevant to your work. However, the first five form a natural sequence. Also, the first is particularly simple and introductory. Example data are provided with the cookbook so that you can work through the recipes yourself. On Starlink systems these example data are kept in directory:

/star/examples/sc17

All the files in this directory should be copied into your current directory before attempting any of the recipes. You might wish to create a new, empty directory for this purpose. You should also ensure that your terminal or workstation is configured to receive X-output.

All the recipes in this part of the cookbook use observations of the type I Seyfert Galaxy NGC 1275 (also known as 3C 84). The J2000 coordinates of this galaxy are:

$\alpha =$ $3h\phantom{\rule{0.3em}{0ex}}19m\phantom{\rule{0.3em}{0ex}}48\text{}s\phantom{\rule{0.3em}{0ex}}\phantom{\rule{0.3em}{0ex}}.\text{}16$,    $\delta =$ $+41\circ \phantom{\rule{0.3em}{0ex}}3{0}^{\prime }\phantom{\rule{0.3em}{0ex}}42\text{′′}1$

Its V magnitude is 12.5 and its morphological classification Ep (these details were obtained from SIMBAD8).