我們利用2微米巡天觀測(2MASS)資料庫的點源目錄，研究太陽附近疏散星團的空間結構。Dias(2003)匯集了目前銀河系當中可見光疏散星團的文獻研究，但是觀測系統彼此的差異，會造成研究星團的誤差。所以為了進一步研究星團的動力演化和星際位置對星團的影響，我們利用2MASS的點源目錄，以徑向密度分佈圖，重新定義星團的大小，也討論以不同的分析方法定義星團大小的差異性。我們透過研究不同參數的相關性，發現愈年老的星團，星團的直徑愈大，星數密度愈低；年老星團分佈的位置離銀河盤面比較高。另一方面，我們也嘗試估計星團的主序星光度函數和主序星質量函數，但是因為研究的樣本太少，並未看到星團演化對星團的光度函數和質量函數的影響。我們也粗略地估計2MASS對研究星團的主序星光度函數以及主序星質量函數的靈敏度，發現距離在2 kpc以內，星團年齡小於3億年的星團，是最好的研究對象。另外我們也意外發現一個有趣的結果，以2MASS 研究不同方向的場星光度函數，指數α竟然非常相近，平均值為0.336±0.011。 We use Two Micron All-Sky Survey (2MASS) to study open clusters in the solar neighborhood. Dias (2003) compiles a catalogue of optical open clusters from literature. The error and consistency are difficult to estimate due to different observational systems and resources. In order to study the effect of dynamical evolution and galactic location on open clusters, we use radial density profile from 2MASS point source catalogue to reestimate the size of clusters. We also discuss the difference between different methods. We find that the sizes of old open clusters are larger, and the number densities of them are smaller. Old open clusters are distributed higher from the disk. We work out the main sequence luminosity function and main sequence mass function of 17 open clusters. We do not find the relation between age and luminosity function and mass function. We conclude that in the contest of main sequence luminosity function and mass function, 2MASS data is suitable for clusters within 2 kpc from the sun and age less than 3×108 yr only. Moreover, we find that an interesting result, the power index of field-star luminosity functions on different locations are very similar, the average value is 0.336±0.011.
