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arXiv 0910.3277astro-ph.IM
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VERITAS望远镜的一种新的镜面对准系统

A New Mirror Alignment System for the VERITAS Telescopes

A. McCann, D. Hanna, J. Kildea, M. McCutcheon

摘要:

用于TeV能量的地基伽马射线天文学的成像大气切伦科夫望远镜(IACT)使用面积约为100 m $^2$的反射器作为其主要光学元件。这些镶嵌的反射器包括安装在空间框架上的数百个镜面,以合理的成本实现这种大面积。为了获得足够质量的反射表面,必须使用称为对准的程序来精确地定向每个面。我们在这里描述的对准系统,它使用数字(CCD)相机放置在光学系统的焦点,面对反射器。当望远镜扫描一个以明亮恒星方向为中心的网格点时,相机会获得一系列反射器的图像。当望远镜直接指向恒星时,正确对准的小平面最亮,而当恒星和望远镜指向方向之间的角度是小平面未对准角度的两倍时,未对准的小平面最亮。来自该扫描的数据可用于计算对准每个面所需的调整。我们已经构建了这样一个系统,并在三个VERITAS IACT上进行了测试。利用该系统,望远镜的光学点扩散函数可缩窄30%以上。我们在这里介绍的系统和结果从最初的使用。

英文摘要:

Imaging atmospheric Cherenkov telescopes (IACTs) used for ground-based gamma-ray astronomy at TeV energies use reflectors with areas on the order of 100m$^2$ as their primary optic. These tessellated reflectors comprise hundreds of mirror facets mounted on a space frame to achieve this large area at a reasonable cost. To achieve a reflecting surface of sufficient quality one must precisely orient each facet using a procedure known as alignment. We describe here an alignment system which uses a digital (CCD) camera placed at the focus of the optical system, facing the reflector. The camera acquires a series of images of the reflector while the telescope scans a grid of points centred on the direction of a bright star. Correctly aligned facets are brightest when the telescope is pointed directly at the star, while mis-aligned facets are brightest when the angle between the star and the telescope pointing direction is twice the misalignment angle of the facet. Data from this scan can be used to calculate the adjustments required to align each facet. We have constructed such a system and have tested it on three of the VERITAS IACTs. Using this system the optical point spread functions of the telescopes have been narrowed by more than 30%. We present here a description of the system and results from initial use.

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