Progress on the prevention of stray light and diffraction effects on the Thai National Telescope
Progress on the prevention of stray light and diffraction effects on the Thai National Telescope
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泰国国家望远镜杂散光和衍射效应防治研究进展
DOI：
10.1117/12.2190411
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发表时间：
2015
影响因子：
2.6
通讯作者：
L. Hardy
中科院分区：
文献类型：
--
作者：
C. Buisset;A. Prasit;A. Leckngam;T. Lépine;Saran Poshyajinda;B. Soonthornthum;P. Irawati;A. Richichi;U. Sawangwit;V. Dhillon;L. Hardy
2.4米的泰国国家望远镜（TNT）是泰国国家天文台的主要设施，位于泰国最高的山Doi Inthanon。在TNT上获得的第一批天文图像受到衍射和杂散光的问题：明亮的恒星图像在焦平面上的几弧分内扩散，在明亮的月亮条件下观测时拍摄的图像受到高水平杂散光的污染。我们进行了有针对性的调查，以确定这些问题的根源。这些研究首次包括分析离焦恒星图像的辐照度分布和识别贡献者。我们的结论是，这些明亮的尖峰围绕着明亮的恒星图像，是由于镜面边缘的倒角和波前误差造成的。因此，我们沿着主镜的边缘安装了一个环形掩模，以完全抑制这些峰值，并通过观察双星天狼星来量化改善。第二次，我们通过在TNT焦平面上放置针孔摄像机来确定杂散光的来源。然后，我们设计了一个新的挡板，以提高杂散光的抑制。挡板的最终设计包括21个隔板，涂上普通的黑色涂料，在不到8个月的时间内设计、开发并安装在TNT上。我们通过测量在望远镜结构中安装挡板前后杂散光信号的变化来评估其性能的改善。这些步骤显著改善了图像质量，增强了焦平面上杂散光的抑制。在本文中，我们介绍了我们的研究，我们描述了TNT挡板的设计方法，并提出了改进的定量术语。
The 2.4-m Thai National Telescope (TNT) is the main facility of the Thai National Observatory located on the Doi Inthanon, Thailand's highest mountain. The first astronomical images obtained at the TNT suffered from diffraction and stray light problems: bright spikes spread from bright stellar images over few arcminutes in the focal plane, and the images taken during observations in bright moon conditions were contaminated by high levels of stray light. We performed targeted investigations to identify the origin of these problems. In a first time, these investigations consisted of analyzing the irradiance distribution of defocused stellar images and of identifying the contributors. We concluded that these bright spikes around the bright stellar images were due to the chamfer and the wavefront error at the mirror edge. We thus installed an annular mask along the edge of the primary mirror that fully suppressed these spikes and we quantified the improvement by observing the double star Sirius. In a second time, we identified the contributors to the stray light by placing a pinhole camera at the TNT focal plane. Then, we designed a new baffle to improve the stray light rejection. The final design of the baffle comprises 21 diaphragms, is painted with an ordinary black paint and was designed, developed and installed on the TNT in less than 8 months. We assessed the improvement on the performance by measuring the variation of the stray light signal before and after installing the baffle in the telescope structure. These steps significantly improved the image quality and enhanced the rejection of the stray light at the focal plane level. In this paper, we present our investigations, we describe the method used to design the TNT baffle, and we present the improvement in quantitative terms.