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Basden A.G.,South Road
Monthly Notices of the Royal Astronomical Society | Year: 2015

The performance of a wide-field adaptive optics system depends on input design parameters. Here we investigate the performance of a multiconjugate adaptive optics system design for the European Extremely Large Telescope, using an end-to-end Monte Carlo adaptive optics simulation tool, DASP (Durham adaptive optics simulation platform).We consider parameters such as the number of laser guide stars, sodium layer depth, wavefront sensor pixel scale, number of deformable mirrors (DMs), mirror conjugation and actuator pitch. We provide potential areas where costs savings can be made, and investigate trade-offs between performance and cost. We conclude that a six-laser guide star system using three DMs seems to be a sweet spot for performance and cost compromise. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Bouwens R.J.,Leiden University | Bouwens R.J.,University of California at Santa Cruz | Illingworth G.D.,University of California at Santa Cruz | Oesch P.A.,Yale University | And 4 more authors.
Astrophysical Journal | Year: 2015

Thomson optical depth τ measurements from Planck provide new insights into the reionization of the universe. In pursuit of model-independent constraints on the properties of the ionizing sources, we determine the empirical evolution of the cosmic ionizing emissivity. We use a simple two-parameter model to map out the evolution in the emissivity at z ≲ 6 from the new Planck optical depth τ measurements, from the constraints provided by quasar absorption spectra and from the prevalence of Lyα emission in z ∼ 7-8 galaxies. We find the redshift evolution in the emissivity required by the observations to be (d log10 Nion/dz)z=8 = -0.15-0.11 +0.08((d log10 Nion/dz)z=8 = -0.19-0.11 +0.09, largely independent of the assumed clumping factor CH ii and entirely independent of the nature of the ionizing sources. The trend in is well-matched by the evolution of the galaxy UV-luminosity density (d log10φUV/dz = -0.11 ± 0.04) to a magnitude limit ≲-13 mag, suggesting that galaxies are the sources that drive the reionization of the universe. The role of galaxies is further strengthened by the conversion from the UV luminosity density ρUV to being possible for physically plausible values of the ESCape fraction fESC, the Lyman-continuum photon production efficiency ξion, and faint-end cut-off Mlim to the luminosity function. Quasars/active galactic nuclei appear to match neither the redshift evolution nor normalization of the ionizing emissivity. Based on the inferred evolution in the ionizing emissivity, we estimate that the z ∼ 10 UV-Iuminosity density is 8-4 +15× lower than at z ∼ 6, consistent with the observations. The present approach of contrasting the inferred evolution of the ionizing emissivity with that of the galaxy UV luminosity density adds to the growing observational evidence that faint, star-forming galaxies drive the reionization of the universe. © 2015. The American Astronomical Society. All rights reserved. Source


Basden A.G.,South Road
Monthly Notices of the Royal Astronomical Society | Year: 2014

Planned instruments utilizing multi-object adaptive optics systems on the forthcoming extremely large telescopes require large numbers of high order deformable mirrors. These devices are a significant cost driver, particularly if specifications regarding the number of faulty actuators are stringent. Here, we investigate the effect on adaptive optics performance that such faulty actuators have, and draw conclusions about how far faulty actuator specifications (and hence cost) can be relaxed without having a significant effect on adaptive optics performance. We also provide performance estimates using a map of faulty actuators from an existing deformable mirror. We investigate the effect of faulty actuators using an end-to-end Monte Carlo adaptive optics simulation code.We find that for actuators stuck at a fixed height above the deformable mirror surface, between 1 and 2 per cent of actuators can be faulty before significant performance degradation occurs. For actuators that are a coupled to nearest neighbours, up to about 5 per cent, can be faulty before adaptive optics (AO) performance begins to be affected. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Basden A.,South Road
Monthly Notices of the Royal Astronomical Society | Year: 2014

In this paper we introduce the concept of real-time hardware-in-the-loop simulation for astronomical adaptive optics, and present the case for the requirement for such a facility. This real-time simulation, when linkedwith an adaptive optics real-time control system, provides an essential tool for the validation, verification and integration of the Extremely Large Telescope real-time control systems prior to commissioning at the telescope. We demonstrate that such a facility is crucial for the success of the future extremely large telescopes. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Jia P.,Taiyuan University of Technology | Cai D.,Taiyuan University of Technology | Wang D.,Taiyuan University of Technology | Basden A.,South Road
Monthly Notices of the Royal Astronomical Society | Year: 2015

High-fidelity Monte Carlo simulation of atmospheric turbulence phase screens is important for performance testing of astronomical adaptive optics systems. With a sparse spectrum model and an optimal sampling method, it is possible to generate an atmospheric turbulence phase screen with high fidelity. However, the phase screen generation speed is limited by the algorithm structure of this technique. A non-uniform fast Fourier transform technique is proposed in this paper to accelerate phase screen generation speed. This method is able to generate huge atmospheric turbulence phase screens with high fidelity and an acceptable time-cost enabling practical adaptive optics simulations of forthcoming Extremely Large Telescopes. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

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