WALOP - South：用于PASIPHAE巡天的四相机单次成像偏振计。论文III——点扩散函数建模
WALOP-South: a four camera one shot imaging polarimeter for the PASIPHAE survey. Paper III -- PSF modelling
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中文总结 AI 辅助
本文针对WALOP型宽视场偏振计，提出基于偏振形小波的点扩散函数测光框架及高效建模方法，通过处理星体质心位移实现高精度测光，满足PASIPHAE巡天偏振科学要求。
中文摘要 AI 辅助
为PASIPHAE巡天建造的两台WALOP仪器，将在SDSS - r波段测量银极区域大量恒星的线偏振。它们具有宽视场设计，WALOP - South能在35′×35′天空区域、WALOP - North能在30′×30′区域同时测量多颗恒星的斯托克斯参数I、q和u。本文提出基于偏振形小波的点扩散函数测光框架用于WALOP型宽视场偏振计中采样良好的恒星点源。偏振形小波由高斯 - 厄米特或高斯 - 拉盖尔多项式构建，适合紧凑高效地建模局部点扩散函数。利用Zemax模拟图像开发了用偏振形小波重建点扩散函数空间变化的高效方法，通过两步迭代法处理星体质心随机亚像素位移。应用于目标暗星时，测光精度可达约0.15%，重建的点扩散函数模型可用于不同视宁度条件下的测光，满足PASIPHAE巡天的偏振科学要求。
英文摘要
The two WALOP instruments, built for the PASIPHAE survey, will measure the linear polarization of large numbers of stars in the Galactic polar regions in the SDSS-$r$ band. They are designed with a wide field-of-view, enabling measurement of the Stokes parameters $I$, $q$, and $u$ for multiple stars simultaneously within a $35^\prime \times 35^\prime$ region of sky for WALOP-South and $30^\prime \times 30^\prime$ region for WALOP-North. In this paper, we present a polar shapelet-based PSF photometry framework for well-sampled stellar point sources applicable to WALOP-type wide-field polarimeters. Polar shapelets are a set of orthogonal basis functions, constructed from Gauss-Hermite or Gauss-Laguerre polynomials, that are well-suited to modelling localized PSF in a compact and efficient way. We developed an efficient PSF modelling method that uses polar shapelets as basis functions to reconstruct the spatial variation of the PSF shape across the CCD using Zemax-simulated images of one of the WALOP instruments, and show that a limited number of shapelet coefficients are sufficient to capture this variation consistently across different CCD locations. To simulate realistic star images, we introduce random sub-pixel shifts in the star centroids in the Zemax-simulated images, and account for this using a two-step iterative method that alternately estimates the PSF model and the sub-pixel centroid shift. Applying PSF photometry to the target faint stars, we demonstrate that the photometric accuracy of approximately 0.15% is achievable, and that the reconstructed PSF model can be incorporated into the photometry across different seeing conditions, meeting the polarimetric science requirements of the PASIPHAE survey.
