η变色龙：反常的初始质量函数还是动力学演化？
eta Chameleontis: abnormal initial mass function or dynamical evolution?
摘要：
Eta Chamaeleontis是一个独特的年轻（约900万年前）的组合，有18个系统集中在半径约35弧分，即1pc的集群距离为97pc。在距离星团中心1.5度的范围内没有发现其他成员。星团的质量函数与其他在较高质量范围内的年轻疏散星团的IMF一致，但明显缺乏低质量恒星和棕矮星，没有低于0.1 Msun的天体。本文的目的是测试这种特殊的质量函数是否可能导致动力学演化，尽管年轻的集群。我们进行了N体数值计算开始与对数正态IMF和不同的初始条件下，使用代码NBODY3的系统和集群半径的数量。我们模拟了超过1000万年的星系团动力学演化，并将结果与观测结果进行了比较。我们发现，当从一个非常紧凑的构型（Ninit=40，R0=0.005pc）开始时，有可能重现eta Cha，这表明该协会的IMF可能不是异常的。高的初始密度也可以解释在星团中观测到的宽双星的不足。
英文摘要：
Eta Chamaeleontis is a unique young (~9 Myr) association with 18 systems concentrated in a radius of ~35 arcmin, i.e. 1pc at the cluster distance of 97pc. No other members have been found up to 1.5 degrees from the cluster centre. The cluster mass function is consistent with the IMF of other rich young open clusters in the higher mass range but shows a clear deficit of low mass stars and brown dwarfs with no objects below 0.1Msun. The aim of this paper is to test whether this peculiar mass function could result from dynamical evolution despite the young age of the cluster. We performed N-body numerical calculations starting with a log-normal IMF and different initial conditions in terms of number of systems and cluster radius using the code NBODY3. We simulated the cluster dynamical evolution over 10 Myr and compared the results to the observations. We found that it is possible to reproduce eta Cha when starting with a very compact configuration (with Ninit=40 and R0=0.005pc) which suggests that the IMF of the association might not be abnormal. The high initial density might also explain the deficit of wide binaries that is observed in the cluster.
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