Introduction

The observations described in Chapter 3 were of relatively bright stars using a conventional high frame rate CCD camera. The readout noise present at these high frame rates would have led to poor signal-to-noise ratios for observations of faint sources.

CCDs recently developed by both E2V Technologies (Jerram et al. , 2001; Harris et al. , 2000) and Texas Instruments (Hynecek & Nishiwaki, 2002) with essentially zero readout noise at low light levels seem particularly well suited to high frame rate imaging techniques like the Lucky Exposures method. Craig Mackay acquired a number of these devices at the Institute of Astronomy, and developed a camera designed to operate them at fast readout rates. This seemed an excellent instrument for testing the performance of the Lucky Exposures technique for imaging faint astronomical targets.

Before undertaking any astronomical observations with this camera, an assessment was made of the expected signal-to-noise performance at low light levels. Two simple numerical models of the output register from one of the E2V L3Vision CCDs were developed by the author in order to make estimates of the signal-to-noise. Detailed descriptions of the statistical properties of these models are presented in this chapter.

The astronomical observations undertaken using the camera will be introduced in Chapter 5. However, a small section of example data from one of the observing runs is introduced in the current chapter, in order that I can compare the statistical properties of the data with the properties of my theoretical models.

In this chapter I will develop models for the expected distributions of output electrons from these CCDs. These models will be of use to future researchers wishing to simulate the performance of the devices. These models are also used to estimate the performance of photon-counting approaches with one run of data taken at the NOT .

In this chapter I also briefly discuss measurements of the charge transfer efficiency of the camera at low signal levels which were undertaken in the laboratory after the first observations at the NOT. These results will be of use in discussions of observational data in later chapters.