一米红外太阳望远镜近场视宁度的研究

As the telescope working，Earth-based Solar telescope and its accessories will be warmed by solar radiation and that would produce atmospheric turbulence around the telescope.The descriptive Parameter to the degradation of the astronomical image quality affected by turbulence of near the telescope tube is defined as near-field seeing and it will negatively affect the image quality..Cement surface of Solar telescope building will be warmed to 40 degrees Celsius above under strong solar radiation. The sealing windows of telescope also have a large range of temperature fluctuation and temperature gradient.Through measurements and simulation, Our studies suggest that the atmospheric turbulence near the telescope tube, caused by hot surfaces of Solar telescope building and sealing windows, have a serious impact on the image quality. As the wind weakening，the astronomical image observed from the 1m infrared solar telescope will have degradation of image quality after working some time，and it can be promoted by closing dome and wind-cooling the telescope.. This study aims to improve the near-field seeing and it can fully take advantage of high quality seeing of the Fuxian Lake Observatory. so that even if the wind is weak,the telescope would still observe high-resolution images,and this would be full of practical significance for improving efficiency of the telescope and extend the high resolution observation time，especially in high-resolution observing of solar active regions for long time.

地基式太阳望远镜及周边设施在观测时会被太阳辐射加热，进而在其周边空气中形成明显的大气湍流。望远镜受镜筒附近光路中的空气湍流影响而产生的像质衰减程度我们称之为近场视宁度，近场视宁度的存在使望远镜的观测能力大打折扣。.强烈的太阳辐射下，一米红外太阳望远镜建筑物的水泥表面会被加热到40摄氏度以上，望远镜封窗也会出现较大的温度起伏和空间梯度。实测及仿真研究显示，风速较小时，封窗和建筑表面发热在镜筒附近引起的空气湍流会严重影响望远镜的成像质量。一米红外太阳望远镜运行中也发现，在风速较小等天气情况下，观测图像会出现不同程度的整体性像质衰减，关闭圆顶并对望远镜通风冷却一段时间后，像质会有改善。.本项目旨在改善一米红外太阳望远镜的近场视宁度，使望远镜在风速较小时也有优良的高分辨成像质量。此问题的解决对提高望远镜的使用效率，延长高分辨观测时间，尤其对太阳活动区进行长时间连续的高分辨观测，具有重要的现实意义。

一米红外太阳望远镜（New Vacuum Solar Telescope ，简称NVST）于2011年投入常规运行。NVST运行中发现，在风速较小天气情况下，观测图像会出现不同程度的整体性像质衰减，关闭圆顶并对望远镜通风冷却一段时间后，像质会有改善。测温显示，强烈的太阳辐射下，NVST周边的沥青表面会被加热到70℃，水泥表面、黑色海绵、地板、瓷砖等也是高温热源。本项目对望远镜及周边热源引起的近场视宁度问题开展了深入的研究。首先对望远镜及周边热环境进行了实测分析，然后基于实测数据对封窗视宁度和热致像差进行了仿真分析。根据仿真结果，给出了封窗冷却液的最佳温度，研制了封窗主动热控系统。搭建了望远镜建筑表面主动热控系统。实际运行中发现，楼顶水池无法被太阳辐射加热至接近气温，水表温度一直远低于气温。基金实施中改用为一种辐射涂层控温法，较好的改善了热源引起的近场空气湍流对像质影响。该项目的研究结果表明：在站址平均自然风速时，封窗热控系统对封窗视宁度改善效果可以忽略；封窗热控系统可以改善封窗热致像差；辐射涂层是抑制周边热源与空气的温差，进而改善望远镜近场视宁度的一种可行方法。