通过球状尘埃测试光学偏振模型的范式示例
Paradigmatic examples for testing models of optical light polarization by spheroidal dust
AI总结：
提出在三维蒙特卡罗辐射传输代码中实现并测试球状尘埃颗粒引起的辐射偏振的通用框架，推导解析解进行基准验证，证明 MCpol 代码与解析解在 0.1% 内一致。
摘要：
我们提出了一个通用框架，说明如何在三维蒙特卡罗辐射传输（MCRT）代码中实现和测试由排列的球状尘埃颗粒的散射、二向色性消光和双折射引起的辐射偏振。我们推导了一种方法，用于求解控制尘埃包裹天体中 Stokes 参数变化的辐射传输方程。我们利用 Müller 矩阵，以及球状颗粒和电子的消光、散射、线偏振和圆偏振截面。我们使用了一个已建立的 MCRT 代码，并扩展其功能以包含 Stokes 形式体系。我们计算了球状颗粒上散射、二向色性消光和双折射引起的光偏振状态变化。处理了光学深度和反照率对偏振的依赖性。描述了球状颗粒的散射实现，包括随机游走步骤和定向散射（剥离）。通过离开模型空间的光子包的角度分箱方法，以及用于生成图像的逆向光线追踪例程，确定了天体可观测的辐射偏振。我们提出了范式示例，并推导了球状尘埃颗粒光学偏振的解析解。这些测试适用于 MCpol 和其他此类代码的基准验证，并允许量化所达到的数值精度。我们证明，与解析解相比，MCpol 在 Stokes 参数上达到了 0.1% 以内的极好一致性。
英文摘要：
We present a general framework on how the polarization of radiation due to scattering, dichroic extinction, and birefringence of aligned spheroidal dust grains can be implemented and tested in 3D Monte Carlo radiative transfer (MCRT) codes. We derive a methodology for solving the radiative transfer equation governing the changes of the Stokes parameters in dust-enshrouded objects. We utilize the Müller matrix, and the extinction, scattering, linear, and circular polarization cross sections of spheroidal grains as well as electrons. An established MCRT code is used and its capabilities are extended to include the Stokes formalism. We compute changes in the polarization state of the light by scattering, dichroic extinction, and birefringence on spheroidal grains. The dependency of the optical depth and the albedo on the polarization is treated. The implementation of scattering by spheroidal grains both for random walk steps as well as for directed scattering (peel-off) are described. The observable polarization of radiation of the objects is determined through an angle binning method for photon packages leaving the model space as well as through an inverse ray-tracing routine for the generation of images. We present paradigmatic examples for which we derive analytical solutions of the optical light polarization by spheroidal dust particles. These tests are suited for benchmark verification of MCpol and other such codes, and allow to quantify the numerical precision reached. We demonstrate that MCpol is in excellent agreement to within 0.1% of the Stokes parameters when compared to the analytical solutions.
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