We have analyzed the application of frame selection ("lucky imaging") to adaptive optics (AO), short-exposure
observations of faint companions. We have used the instantaneous Strehl ratio as an image quality metric. The
probability density function (PDF) of this quantity can be used to determine the outcome of frame selection in terms of
optimizing the Strehl ratio and the peak-signal-to-noise-ratio of the shift-and-add image. In the presence of static
speckles, frame selection can lead to both: improvement in resolution--as quantified by the Strehl ratio, as well as faint
signal detectability--given by the peak-signal-to-noise-ratio. This theoretical prediction is confirmed with real data from
AO observations using Lick Observatory's 3m Shane telescope, and the Palomar Observatory's 5m Hale telescope. In
addition, we propose a novel statistics-based technique for the detection of faint companions from a sequence of AO-corrected
exposures. The algorithm, which we call stochastic speckle discrimination, utilizes the "statistical signature" of
the centre of the point spread function (PSF) to discriminate between faint companions and static speckles. The
technique yields excellent results even for signals invisible in the shift-and-add images.
We report on the development of instrument concepts for a European ELT, expanding on studies carried out as part of the ESO OWL concept. A range of instruments were chosen to demonstrate how an ELT could meet or approach the goals generated by the OPTICON science team, and used to push the specifications and requirements of telescope and adaptive optics systems. Preliminary conclusions are presented, along with a plan for further more detailed instrument design and technology developments. This activity is supported by the European Community (Framework Programme 6, ELT Design Study, contract number 011863).
We have investigated both the temporal and spatial structure of the point spread function (PSF) produced by the Lick
Observatory adaptive optics (AO) system using the FastSub readout mode of the IRCAL camera using short-exposure
images with exposure times of 22ms at a frame rate of ~ 20Hz suitable for "freezing" the compensation under typical K-band
observing conditions. These short exposures are a useful diagnostic tool for determining the system performance
and permit measurement of the instantaneous Strehl ratio. Data taken from a number of observing runs, spanning over
four months, show the underlying morphology of the PSF to be very stable with instantaneous Strehl ratios varying from
~ 20%-70% in NGS mode. Estimates of the instantaneous Strehl distribution have also been obtained from which we
have determined the probability density function for the distribution of the instantaneous Strehl ratios.
A system is described which makes best use of the high quantum efficiency and high count rate capability of avalanche
photodiodes for high time resolution observations of optical pulsars. The use of three APDs allows simultaneous photometry
of the target and a reference star, and the monitoring of the sky background. By minimising the optical components in
the light path the optical efficiency of the system is maximised. The TRIFFID1 and OPTIMA2 have shown that fibre-fed APD arrays can produce excellent results. This, new, system was used on the 6m BTA in November 2003-results on the
Crab pulsar are presented.
A new use for a 2-dimensional position sensitive diode (PSD) is described. A duolateral PSD was used with a microchannel
plate image intensifier as a proof-of-concept photon counting (event driven) imager for astronomical imaging and photometry.
This produced an imager capable of counting 25-30 kcps over the astronomical bands B, V & R, with an overall
efficiency of ~19%.
National monuments are at ever-increasing risk of severe and permanent damage. The 3D laser scanning of stone monuments brings a new dimension in the field of cultural heritage by providing means of preserving, visualizing, accessing and analysing some of its most invaluable artefacts. In this article, we present the results obtained with our project "Profilometry of Medieval Irish Stone Monuments" hosted at the Centre for the Study of Human Settlement and Historical Change, NUI Galway. This project aims to create a virtual archive of selected incised stones from 3D scans taken in the field. The raw scans are processed into watertight 3D models and new processing techniques have been developed to enhance the surface features of the stones. Also, textured 3D models of the artefacts have been made available online for the benefit of both the historian community and the broader public. This article focuses on the analysis we performed on the shaft of the east cross at Toureen Peacaun, Co Tipperary, which shows the longest inscription in Ireland with geometrical capitals.