标题： 测量大气对微小视差影响的作用：一种应用于宽视场CCD帧的简单方法 显示英文标题

标题： Measuring the Atmospheric Influence on Differential Astrometry: a Simple Method Applied to Wide Field CCD Frames

摘要： 使用短曝光时间的导引CCD帧来测量由大气层引入到微小测角观测中的噪声。在KPNO和CTIO 0.9米望远镜两年的数据中发现了与视宁度相关的显著夜变现象。经过对原始$x,y$数据的线性变换后，发现由大气层引入的均方根噪声为3到7毫角秒（以100秒曝光时间和天顶附近的20角分视场为基准）。对于KPNO，还发现了一个额外的接近恒定的噪声（基底噪声），即8.5毫角秒=0.012像素；而对于CTIO望远镜，则为6.0毫角秒=0.015像素。这意味着基于地面的全天空微小测角巡天，从导引CCD帧获得的数据更可能受到基底噪声的限制而非大气影响，并且在良好视宁度条件下可以达到优于10毫角秒的精度。 显示英文摘要

摘要： Sets of short exposure, guided CCD frames are used to measure the noise added by the atmosphere to differential astrometric observations. Large nightly variations that are correlated with the seeing have been found in the data obtained over 2 years at the KPNO and CTIO 0.9-meter telescopes. The rms noise added by the atmosphere, after a linear transformation of the raw $x,y$ data, is found to be 3 to 7 mas, normalized to 100 seconds exposure time and a field of view of 20 arcminutes near the zenith. An additional nearly constant noise (base-level) of 8.5 mas = 0.012 pixel is found for the KPNO and 6.0 mas = 0.015 pixel for the CTIO telescope. This implies that a ground-based, all sky, astrometric survey from guided CCD frames is more likely limited by the base-level noise than by the atmosphere and could reach an accuracy better than 10 mas under good seeing conditions.