Performance modeling and development of an L3-CCD camera system for high cadence imaging with maximum efficiency

High-cadence imaging is required in several astronomical scenarios. These include: studies of rapidly varying sources, achieving maximum signal-to-noise observations of bright objects, and high dynamic range scenarios, such as faint objects embedded in a crowded field of bright objects. Conventional CCDs have drawbacks in this regime, because many short exposures are needed (either for timeseries sampling, or simply to avoid saturation), with extended readout times between exposures. Consequently, the duty cycle (ratio of exposure time to readout time) dramatically worsens as exposures get shorter. However, Low Light Level CCDs (L3-CCDs) offer low readout noise, high readout rates, and 100% duty cycle. Coupled with its fast frame-transfer mechanism (∼2ms to shift the image to the storage area), an L3-CCD can sustain essentially continuous open-shutter time. Our models demonstrate that for a fixed observing time, the L3-CCD will deliver a better signal to noise performance in the high-cadence imaging regime when compared to similar CCDs, even when the latter's performance is optimised by windowing and binning. We also demonstrate that the improved duty cycle reduces the photometric impact of atmospheric scintillation, for any given aperture of telescope. We outline the integration of an L3-CCD into our camera system for high cadence imaging.