The MSSSO Wide Field CCD H Imaging Survey

Introduction

H emission is an important tracer of ionised circumstellar or interstellar material. H surveys have traditionally been used to find Be stars, T Tauri stars, Mira variables, interacting binaries and planetary nebulae. Emission in H is also used as a tracer of star formation in external galaxies and for studies of the conditions and dynamics of the ionised interstellar medium.

Previous H surveys of the Galaxy have been performed with photographic plates or film. This provided reasonably large fields with good pixel resolution. However, this medium suffers from being non-linear with a limited dynamic range, low quantum efficiency (1-5%) and the existence of reciprocity failure. On the other hand, CCDs are linear, have a large dynamic range and high quantum efficiency (60-80%). They are normally much smaller in size than plates of film and have a lower pixel resolution. Larger CCDs are now available (with corresponding small pixel sizes), and by using new techniques of drift scanning (Zaritsky et al. 1996) they are increasingly being used for large-scale surveys.

The Wide Field H Survey will be important in two ways. First, comparison with the Molonglo Observatory Synthesis Telescope (MOST) radio continuum images at 843 MHz will help us to understand the nature of both radio and optical sources in and beyond the Galactic Plane. Secondly, calibration of the optical images shall enable us to produce quantitative information which has not been previously obtainable on this scale.

This paper shall describe the aims of the project, the instrumentation used and our plan of observations. We shall also describe the reduction of data and how our optical images will be compared to the MOST radio data.

© Copyright Astronomical Society of Australia 1997