迭代角微分成像（IADI）：用迭代ADI方法在散射光中恢复盘结构的探索
Iterative Angular Differential Imaging (IADI): An exploration of recovering disk structures in scattered light with an iterative ADI approach
摘要：
在近红外线波段区分年轻的富气星周盘信号和恒星信号是一个困难的任务。诸如角度差分成像（ADI）和偏振差分成像（PDI）的当前技术应对诸如自减影的缺点。为了解决这些缺点，我们探索迭代角差分成像（IADI）技术，以增加总强度观测的信号吞吐量。本工作旨在探索IADI的有效性恢复磁盘的自减区域迭代应用ADI技术。为了确定IADI的有效性，建立了磁盘图像的模型，并用IADI进行了后处理。此外，还研究了基于极化图像的掩蔽方法和反馈信号的信号阈值。不对称是恢复磁盘的一个非常重要的因素，因为数据集中的磁盘重叠较少。在某些情况下，与ADI相比，IADI可以恢复75倍以上的通量。使用Procrustes距离来量化算法对散射相函数的影响。根据噪声水平和恒星信号与盘信号之间的比率，相位函数可以恢复比标准ADI更好的Procrustes距离的6.4倍。由于多次迭代，确实发生了图像上的噪声放大和拖尾，并且通过使用二进制掩码和动态阈值，这种反馈被减轻，但它仍然是最终流水线中的一个问题。最后，用VLT/SPHERE对原行星盘进行了观测，并用IADI进行了处理，得到了很有希望的结果。虽然由于噪声放大和恒星重建，IADI在低信噪比观测方面存在问题，但相对于标准ADI，高信噪比观测显示出有希望的结果。
英文摘要：
Distinguishing signal of young gas rich circumstellar disks from stellar signal in near infrared light is a difficult task. Current techniques such as Angular Differential Imaging (ADI) and Polarimetric Differential Imaging (PDI) cope with drawbacks such as self-subtraction. To address these drawbacks we explore Iterative Angular Differential Imaging (IADI) techniques to increase signal throughput in total intensity observations. This work aims to explore the effectiveness of IADI to recover the self-subtracted regions of disks by applying ADI techniques iteratively. To determine the effectiveness of IADI a model of a disk image is made and post-processed with IADI. In addition, masking based on polarimetric images and a signal threshold for feeding back signal are explored. Asymmetries are a very important factor in recovering the disk due to less overlap of the disk in the data set. In some cases, a factor 75 more flux could be recovered with IADI compared to ADI. The Procrustes distance is used to quantify the impact of the algorithm on the scattering phase function. Depending on the level of noise and the ratio between the stellar signal and disk signal, the phase function can be recovered a factor 6.4 in Procrustes distance better than standard ADI. The amplification and smearing of noise over the image due to many iterations did occur and by using binary masks and a dynamic threshold this feedback was mitigated, but it still is a problem in the final pipeline. Lastly observations of protoplanetary disks made with VLT/SPHERE were processed with IADI giving rise to very promising results. While IADI has problems with low signal-to-noise observations due to noise amplification and star reconstruction, higher signal-to-noise observations show promising results with respect to standard ADI.
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