标题： UCAC3 像素处理 显示英文标题

标题： UCAC3 pixel processing

摘要： 第三次美国海军天文台（USNO）CCD天体照相星表UCAC3于2009年8月10日在国际天文学联合会大会期间发布。 它是一个高精度的全天天体测量星表，包含约一亿颗恒星，其视星等范围为R = 8到16。 近期历元观测基于超过270,000张CCD曝光图像，在UCAC3发布时应用了传统和新技术对这些图像进行了重新处理。 数据中的挑战包括由于探测器电荷转移效率差导致的高暗电流和非对称图像轮廓。 探索了非高斯图像轮廓函数，并发现轮廓拟合参数与CCD帧属性之间存在相关性。 这些被用来约束图像轮廓拟合模型，并用最少的自由参数充分描述了恒星图像的观测点扩散函数。 使用适当模型函数，双星的混合图像可以成功拟合。 UCAC3的位置是通过二维图像轮廓拟合得到的，采用了一个五参数对称洛伦兹轮廓模型。 发现内部精度约为每坐标5毫角秒，单次曝光下也是如此，但受大气影响降为约10毫角秒。 然而，在x,y数据中存在超过100毫角秒的系统误差，在此处描述的x,y数据减少步骤之后的天体测量减少过程中已对此进行了修正。 显示英文摘要

摘要： The third US Naval Observatory (USNO) CCD Astrograph Catalog, UCAC3 was released at the IAU General Assembly on 2009 August 10. It is a highly accurate, all-sky astrometric catalog of about 100 million stars in the R = 8 to 16 magnitude range. Recent epoch observations are based on over 270,000 CCD exposures, which have been re-processed for the UCAC3 release applying traditional and new techniques. Challenges in the data have been high dark current and asymmetric image profiles due to the poor charge transfer efficiency of the detector. Non-Gaussian image profile functions were explored and correlations are found for profile fit parameters with properties of the CCD frames. These were utilized to constrain the image profile fit models and adequately describe the observed point-spread function of stellar images with a minimum number of free parameters. Using an appropriate model function, blended images of double stars could be fit successfully. UCAC3 positions are derived from 2-dimensional image profile fits with a 5-parameter, symmetric Lorentz profile model. Internal precisions of about 5 mas per coordinate and single exposure are found, which are degraded by the atmosphere to about 10 mas. However, systematic errors exceeding 100 mas are present in the x,y-data which have been corrected in the astrometric reductions following the x,y-data reduction step described here.