| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 100 === Membership identi cation is the critical rst step to determine the properties of a star cluster. Low-mass members in particular could be used to trace the dynamical history | mass segregation, stellar evaporation, tidal stripping of a star cluster in its Galactic environment. We have initiated a program to identify members in star clusters by photometric and kinematic data sets. Here we show our analysis of the nearby (distance of 170 pc) Praesepe cluster (M 44), by using the 2MASS photometry and the PPMXL proper motions, from which a total of 758 member candidates have been identi ed down to a mass limit of 0.2 M . Even lower mass members were found by using Pan-STARRS1 photometry reaching as faint as gP1 = 22.8 mag, corresponding to 0.1 M . Previous studies of Praesepe member candidates relied on photometry and proper motions of bright stars, and mostly photometry only of faint stars. Our work is the first to select membership down to almost the stellar mass end by both photometric and kinematic criteria. Some member candidates found in previous studies have proper motions inconsistent with that of M44, so should be excluded from membership. Mass segregation is clearly evidenced in this mid-aged (900 Myr) cluster.
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