星團成員星在空間上的位置或運動有類似的表現，視覺上就可以在天空上看到該處有一群星星。我們發展一套方法來用UCAC星表來分辨出星團成員星和場星的不同，並且用兩個例子來展示如何用運動學挑出來的成員星定出比只用光學算出來更精準的星團距離。我們算出來M44的距離是185±10 pc、NGC752是453±10 pc。我們的研究也發現2MASS主序星和巨星的顏色會因為銀盤上有紅化的關係，而在不同銀緯上對星團的修正不一致。這些問題我們在做星團距離的測定時，也一併考慮進去了。 Abstract Members in a star cluster share common location and motion in space, and are seen as grouping in the sky. We have developed a method to use the USNO CCD Astrograph Catalog (UCAC) proper motion database to distinguish probable members in a star cluster against field stars. With a couple of examples, we show how kinematic membership information allows us to better determine the distance of a star cluster than photometry alone. The distance is found to be 185±10 pc for M44, and 453±10 pc for NGC752. In the course of our study, we found inconsistency of the intrinsic 2MASS colors of dwarfs and giants commonly used in the literature, apparently because of reddening in the Galactic plane. This problem has been considered in our distance measurement.
