美国海军天文台照相星表第四批数据释放（UCAC4)

美国海军天文台第四批照相星表UCAC4于2012年8月发布（双面DVD和CDS数据中心Vizier目录I/322），包含超过1.13亿条目，其中超过1.05亿源有自行测量数据。UCAC4是UCAC3的更新版本，其恒星数量大致相同，也覆盖了所有天空。修正了错误，避免了施密特板测量数据，并为大约一半的恒星添加了精确的五波段测光。FK6、Hipparcos和Tycho-2的数据补充了对明亮恒星的星图观测，编制了一个从最亮恒星到大约R=16星等的UCAC4恒星星表。 1998–2004期间观测的位置是通过USNO照相仪20厘米孔径的“红端透镜”的观测获得的，该透镜配备了4k×4k CCD。平均位置和自行是通过将这些观测结果与140多个地面和天基星表相结合得出的，其中包括Hipparcos/Tycho-2和AC2000.2，以及其他天体观测图像中5000多个天区板块的未发表数据。对于南半球的大多数微弱恒星来说，南天自行测量计划中的第一个历元天区构成了自行测量的基础，而北天自行测量计划的第一个历元天区对天空的其他部分起着相同的作用。这些数据由大约1.1亿颗恒星的2MASS近红外测光法和超过5100万颗恒星的五波段（B，V，g，r，i）APASS数据补充。因此，与UCAC3和UCAC2一样，已出版的UCAC4是一个以UCAC观测计划为主要组成部分的汇编目录。根据星等的不同，UCAC4中恒星在平均历元的位置精度约为每个坐标15–100 mas，而自行的理论误差约为1至10 mas/yr，具体取决于星等和观测历史。自行中的系统误差估计约为1-4毫角秒/年（mas/yr）。

The 4th United States Naval Observatory Astrographic Catalog (UCAC4) was released in August 2012 (distributed via double-sided DVD and hosted as the CDS data center Vizier catalog I/322). It contains over 113 million entries, with more than 105 million sources having proper motion measurements. UCAC4 is an updated successor to UCAC3, featuring roughly the same number of stars and full-sky coverage. It corrected prior errors, excluded Schmidt plate measurement data, and added precise five-band photometry for approximately half of its stellar targets. Data from FK6, Hipparcos, and Tycho-2 supplemented astrometric observations of bright stars, compiling a UCAC4 stellar catalog spanning from the brightest stars down to approximately R=16 magnitude.

Positions observed between 1998 and 2004 were acquired using the "red-end lens" of the USNO 20 cm aperture astrograph, which was equipped with a 4k×4k CCD. Average positions and proper motions were derived by combining these observations with over 140 ground-based and space-based catalogs, including Hipparcos/Tycho-2 and AC2000.2, as well as unpublished data from over 5000 sky plates from other astrometric imaging surveys. For most faint stars in the southern hemisphere, the first-epoch plates from the Southern Proper Motion Survey formed the basis for proper motion measurements, while the first-epoch plates from the Northern Proper Motion Survey served the same purpose for the rest of the celestial sphere.

These data were supplemented by 2MASS near-infrared photometry for approximately 110 million stars and five-band (B, V, g, r, i) APASS photometry for over 51 million stars. Thus, like UCAC3 and UCAC2, the published UCAC4 is a compiled catalog primarily centered on the UCAC observing program.

Depending on stellar magnitude, the positional accuracy of stars in UCAC4 at the average epoch is approximately 15–100 mas per coordinate, while the formal uncertainty of proper motions ranges from 1 to 10 mas/yr, depending on stellar magnitude and observational history. Systematic uncertainties in proper motions are estimated to be approximately 1–4 mas per year.

搜集汇总

背景与挑战

背景概述

UCAC4是美国海军天文台发布的第四批照相星表，包含超过1.13亿条恒星条目，覆盖全天空，是UCAC3的更新版本，修正了错误并添加了五波段测光数据。数据集基于1998-2004年观测，结合140多个星表，提供高精度的位置和自行测量，位置精度约15-100 mas，自行误差约1-10 mas/yr，适用于恒星天体测量研究。