Investigating the effect of ground layer adaptive optics on speckle interferometry through computational simulations

Atmospheric turbulence limits the angular resolution of ground-based telescopes far below the diffraction limit. Speckle interferometry (SI) is a technique that recovers diffraction limited information under the turbulent atmosphere. This thesis investigates the performance of SI for recovering the parameters of binary star systems under photon-limited conditions and assesses the gains achievable with ground-layer adaptive optics (GLAO). Speckle images of both binary stars and reference stars were generated through numerical simulation, with atmospheric turbulence modelled by Kolmogorov phase screens. Fourier domain analysis of these images produced the corresponding power spectra, which—after calibration—were used to extract the binary separation, position angle, and intensity ratio, while a least-squares bispectrum algorithm recovered the Fourier phase to resolve the intrinsic 180° orientation ambiguity. Results show that SI reliably recovers binary parameters at high photon counts. Intensity-ratio estimates become biased and increasingly variable as the number of photoevents decreased to approximately 25,000 photoevents. Incorporating GLAO, modelled via removal of up to 120 Zernike modes from one of two phase screens, significantly improved fringe contrast and reduced the number of photoevents required for reliable recovery of binary parameters by more than an order of magnitude. These findings demonstrate that combining SI with GLAO correction enables diffraction limited measurements of binaries at visible wavelengths using relatively low photonevents. The study provides practical thresholds and error estimates for observing faint binaries with 4-m class telescopes and offers a computational framework readily extendable to real observational data and more advanced adaptive-optics configurations.

Publisher

University of Galway

Rights

CC BY-NC-ND

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Collections

University of Galway Theses (Research Masters Theses)