标题： 第三美国海军天文台CCD星图目录（UCAC3） 显示英文标题

标题： The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)

摘要： 第三次美国海军天文台（USNO）CCD天体照相仪星表，UCAC3于2009年8月10日在IAU大会发布。 它是该系列中的第一个全天域发布，包含超过1亿个天体，其中约9500万个天体具有自行，覆盖大约R=8到16等的范围。 当前历元位置是通过使用20厘米孔径的USNO天体照相仪的“红镜”进行观测获得的，该镜配备了4k乘4k的CCD。 自行是通过将这些观测与超过140个地面和空间天体目录相结合得出的，包括Hipparcos/Tycho和AC2000.2，以及来自其他天体照相仪的5000多张底片的未发表测量数据。 对于南半球较暗的恒星，耶鲁/圣胡安首次历元底片来自SPM项目（YSJ1）构成了自行的基础。 这些数据还补充了来自SuperCOSMOS项目的全天域施密特底片巡天的天体测量和测光数据，以及2MASS近红外测光数据。 与UCAC2相比，UCAC3数据的主要差异包括完全新的原始数据处理，对位置系统误差有更严格的控制，显著改进的测光数据，略微更深的极限星等，北天极区域的覆盖，以及通过包含双星和弱检测提高了完整性。 当然，这导致了一个不如UCAC2“干净”的星表，本文中指出了存在问题的区域。 UCAC3中恒星的位置精度约为每坐标15至100毫角秒，而自行误差根据星等和观测历史从1至10毫角秒/年不等，由于重新处理的SPM数据和包含了在UCAC2时期不可用的更多天体照相仪底片数据，与UCAC2相比有显著改进。 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 the first all-sky release in this series and contains just over 100 million objects, about 95 million of them with proper motions, covering about R = 8 to 16 magnitudes. Current epoch positions are obtained from the observations with the 20 cm aperture USNO Astrograph's "red lens", equipped with a 4k by 4k CCD. Proper motions are derived by combining these observations with over 140 ground- and space-based catalogs, including Hipparcos/Tycho and the AC2000.2, as well as unpublished measures of over 5000 plates from other astrographs. For most of the faint stars in the Southern Hemisphere the Yale/San Juan first epoch plates from the SPM program (YSJ1) form the basis for proper motions. These data are supplemented by all-sky Schmidt plate survey astrometry and photometry obtained from the SuperCOSMOS project, as well as 2MASS near-IR photometry. Major differences of UCAC3 data as compared to UCAC2 include a completely new raw data reduction with improved control over systematic errors in positions, significantly improved photometry, slightly deeper limiting magnitude, coverage of the north pole region, greater completeness by inclusion of double stars and weak detections. This of course leads to a catalog which is not as "clean" as UCAC2 and problem areas are outlined for the user in this paper. The positional accuracy of stars in UCAC3 is about 15 to 100 mas per coordinate, depending on magnitude, while the errors in proper motions range from 1 to 10 mas/yr depending on magnitude and observing history, with a significant improvement over UCAC2 achieved due to the re-reduced SPM data and inclusion of more astrograph plate data unavailable at the time of UCAC2.