Ph.D. Defense by Jesper Skottfelt – Niels Bohr Institute - University of Copenhagen

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Ph.D. Defense by Jesper Skottfelt

Title: Improving Lucky Imaging Photometry

High frame-rate imaging can be used to improve the spatial resolution of astronomical observations made at ground-based optical and near-infrared telescopes. Using exposure times of 10-100 ms, the single exposures can be shifted and added, thus mitigating the effect of the atmospheric turbulence. If only the few percent best exposures are used, very high spatial resolution can be achieved; a technique called Lucky Imaging.

Using a conventional CCD for high frame-rate imaging, is usually not feasible due to the high level of readout noise when doing fast readouts.

Instead an electron multiplying CCD (EMCCD) can be used. In an EMCCD the signal is cascade amplified before it is read out, thus rendering the readout noise negligible compared to the signal even at very high readout speeds (10-100 frames/s).

In this thesis I describe the Two-Colour EMCCD Instrument (TCI) that has been designed for the SONG 1m telescopes and for the Danish 1.54m telescope at La Silla. The motivation behind the TCI is to enable simultaneous red and visual band observation, thus providing instantaneous colour information and maximising the detected wavelength range without losing spatial information.

My main contribution has been developing the software for controlling the TCI and reducing the EMCCD data.

With the high spatial resolution that can be achieved with the TCI, it has, among other things, been possible to obtain high precision time-series photometry of crowded fields. I detail the discovery of two previously unknown variable stars in the Galactic globular cluster NGC 6981, and the search for variable stars in further five globular clusters.

Vejleder: Uffe Gråe Jørgensen

Assessment committee:

Anja Andersen, Niels Bohr Institute
Lukasz Wyrzykowski, Warsaw University Astronomical Observatory
Nicholas M. Law, University of North Carolina at Chapel Hill