Speaker
Description
One of the Euclid survey’s primary cosmological probes is weak gravitational lensing: the apparent coherent distortion of galaxies caused by their light passing through gravitational potentials along the line of sight. Obtaining precise and accurate galaxy shapes is therefore crucial for unbiased cosmological inference. The leading source of systematic error in these measurements is the point-spread function (PSF), which can introduce spurious correlations if not modelled accurately.
During survey operations, the main driver of PSF variability is the defocus wavefront error, which affects the PSF size and consequently the apparent roundness of galaxies. We present a fast, purely empirical method to estimate the defocus wavefront error using a simple linear relation between defocus and the lateral displacement of diffraction spikes in bright stars.
This approach enables us to trace the remarkably stable evolution of the Euclid telescope across its full survey timeline. Our defocus estimator provides a tight per-exposure prior for PSF modelling and is generalisable to other diffraction-limited telescopes.
| Other topic / keywords: | Instrumentation |
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