AST3实时自动调焦与利用亮星拖影监测视宁度的研究

Antarctic Survey Telescope×3 (AST3), consisting of three 50cm/68cm modified Schmidt telescopes, are designed for wide field survey in multi optical bands to take advantage of excellent observational conditions at Dome A, Antarctica. The data will contribute to time domain astronomy. The first AST3 was deployed to Dome A on January 2012, and will start observation from March 2012, while the others are scheduled to be installed in the following years. Since currently the KunLun Station at Dome A is unattended during the winter, AST3 have to to be able to run automatically, and need to be controlled remotely, which is so called Robotic Autonomous Observatory. Therefore this project aims at researching and optimizing some key functions for the autonomous observation based on the current run control and data system of AST3. This project will achieve two main goals: 1) monitor the focus of the telescope in real time, detect the best focus and adjust to it automatically; establish a temperature-related focus model for future use; 2) measure and monitor the seeing using the trails of the bright stars during CCD frame transfer. This project will not only improve the image quality and photometric accuracy so as to achieve the scientific goals of AST3, but also for the first time acquire the direct seeing information at Dome A for the astronomical site testing.

南极巡天望远镜AST3由三台50cm/68cm的改正型施密特望远镜组成，将安装在南极冰穹A进行大视场、光学多波段重复巡天，优良的台址将使其数据可以广泛应用于时域天文学的研究。第一台已于2012年1月安装在南极冰穹A，并将在3月开始观测，其他的也将在随后几年安装运行。冰穹A昆仑站的冬季无人值守要求AST3必须全自动运行，并可远程控制。本项目将针对AST3已有的运行控制与数据系统，着重研究及优化自动运行中的两个问题：1）实现望远镜自动实时调焦，并研究焦距与温度、望远镜姿态等的变化规律，建立模型以进行主动调焦；2）利用CCD帧转移时的亮星拖影测量冰穹A视宁度并进行长期监测。研究结果将不仅能够保证AST3观测图像质量和测光精度，实现既定的科学目标，也将得到南极冰穹A的视宁度监测数据，帮助完善冰穹Ａ的台址监测工作。

南极巡天望远镜（Antarctic Survey Telescopes, AST3）是我国在南极昆仑站的第二代光学望远镜，将进行大视场多色巡天和时域天文学研究。本课题目标是为AST3开发自动调焦系统以保证观测图像质量，并研究利用CCD帧转移中的亮星拖影测量大气视宁度，从而实现对南极昆仑站的视宁度监测。本课题主要完成的工作如下：研究了AST3自动调焦方法并实现在南极的实际应用；研究了亮星拖影测量大气视宁度的方法，得到了与DIMM相吻合的结果。为了完成这些工作，结合南极昆仑站无人值守的极端观测条件，必须首先实现自动运行AST3及数据处理等工作。因此，本课题还参与开发了AST3运行控制、CCD图像采集、数据自动存储与管理等软件系统；为了更精确地进行数据处理，在实验室对CCD相机进行了详细的性能测试，发现了光子转移曲线的非线性，提出了charge sharing PSF的概念来描述这一CCD仪器效应；研究了平场、暗流等改正方法，并对第一台AST3 2012年的观测数据进行了处理与发布；此外，对昆仑站的气象条件进行了研究，其温度分层揭示了大气边界层的高度，而风速则会影响亮星拖影的结果。