VLT/FORS1上几天时间尺度的高精度天体测量
High-precision astrometry on the VLT/FORS1 at time scales of few days
摘要：
我们调查的天体测量的精度与VLT/FORS 1相机，并考虑潜在的应用。这项研究是基于两个时代（2000年和2002/2003年）的框架系列的观测选定的银河隆起的天空区域，获得了与FORS 1在连续四个晚上。减少进行了一种新的技术，消除大气图像运动，不需要目标和参考对象之间的区别。天文测量的位置精度被发现只受到恒星光心测定精度的限制，对于明亮的不饱和恒星B=18-19，通常每次测量的光心为200-300微弧秒。几个统计测试表明，在1-4夜的时间尺度上，测量位置的残余噪声基本上是白噪声，没有系统的仪器特征，也没有明显偏离高斯分布。我们的数据表明，配备FORS 1/2相机的VLT可以有效地用于行星微透镜事件的天体测量观测和其他需要高精度的应用，预计50帧（R滤光片1小时）的VLT可以达到30-40微弧秒。
英文摘要：
We investigate the accuracy of astrometric measurements with the VLT/FORS1 camera and consider potential applications. The study is based on two-epoch (2000 and 2002/2003) frame series of observations of a selected Galactic Bulge sky region that were obtained with FORS1 during four consecutive nights each. Reductions were carried out with a novel technique that eliminates atmospheric image motion and does not require a distinction between targets and reference objects. The positional astrometric precision was found to be limited only by the accuracy of the determination of the star photocentre, which is typically 200-300 microarcsec per single measurement for bright unsaturated stars B=18-19. Several statistical tests have shown that at time-scales of 1-4 nights the residual noise in measured positions is essentially a white noise with no systematic instrumental signature and no significant deviation from a Gaussian distribution. Some evidence of a good astrometric quality of the VLT for frames separated by two years has also been found. Our data show that the VLT with FORS1/2 cameras can be effectively used for astrometric observations of planetary microlensing events and other applications where a high accuracy is required, that is expected to reach 30-40 microarcsec for a series of 50 frames (one hours with R filter).
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