PSF modelling for very wide-field CCD astronomy

Abstract

Context.One of the possible approaches to detecting optical counterparts of GRBs requires monitoring large parts of the sky. This idea has gained some instrumental support in recent years, such as with the "Pi of the Sky" project. The broad sky coverage of the "Pi of the Sky" apparatus results from using cameras with wide-angle lenses (20 • × 20 • field of view). Optics of this kind introduce significant deformations of the point spread function (PSF), increasing with the distance from the frame centre. A deformed PSF results in additional uncertainties in data analysis. Aims. Our aim was to create a model describing highly deformed PSF in optical astronomy, allowing uncertainties caused by image deformations to be reduced. Methods. Detailed laboratory measurements of PSF, pixel sensitivity, and pixel response functions were performed. These data were used to create an effective high quality polynomial model of the PSF. Finally, tuning the model and tests in applications to the real sky data were performed. Results. We have developed a PSF model that accurately describes even very deformed stars in our wide-field experiment. The model is suitable for use in any other experiment with similar image deformation, with a simple tuning of its parameters. Applying this model to astrometric procedures results in a significant improvement over standard methods, while basic photometry precision performed with the model is comparable to the results of an optimised aperture algorithm. Additionally, the model was used to search for a weak signal -namely a possible gamma ray burst optical precursor -showing very promising results. Conclusions. Precise modelling of the PSF function significantly improves the astrometric precision and enhances the discovery potential of a wide-field system with lens optics.

PSF Estimation of Space-Variant Ultra-Wide Field of View Imaging Systems

“…Results from all implemented approaches are illustrated in Figure 14. An approach based on work by Piotrowski [1], labeled as the Interpolated Table 4 and ten other points according to the normalized image distance H. The points which are not mentioned in Table 4 are selected similarly as illustrated in Figure 5. The angle ϕ of these points differs from zero.…”

“…Results from all implemented approaches are illustrated in Figure 14. An approach based on work by Piotrowski [1], labeled as the Interpolated Figure 13. Experimental results for the MAXDIFF difference up to the 8th order.…”

“…Results from all implemented approaches are illustrated in Figure 14. An approach based on work by Piotrowski [1], labeled as the Interpolated model, provide results of the MAXDIFF operator from 7.8% to 9.9% over the FOV. Another approach based on Weddel's method [23], labeled as the Sectorized model, which divides the image into smaller invariant parts, provides similar results to the Interpolated model.…”

“…These systems are known as UWFOV systems. The wide-angle optical elements used in UWFOV systems introduce a significant shift variance [1], which complicates the modeling task. Many recent research works have focused on finding a model of UWFOV systems that is suitable for reducing the uncertainties in reconstructing image data from wide-field microscopic systems [2][3][4], security cameras [5][6][7], and all-sky cameras [8][9][10][11][12][13][14][15].…”

Point spread function modelling for wide-field small-aperture telescopes with a denoising autoencoder

“…For WFSATs, the Moffat model can fit the peak of star images, but it can not give promising results for the rest part. Because the field of view of WFSATs is very big, off-axis aberrations will bring highly deformable PSFs, which are hard to be described by circular symmetric functions (Piotrowski et al 2013).…”