Praesepe疏散星团中的褐矮星和极低质量恒星：一个动力学上未演化的质量函数？
Brown dwarfs and very low mass stars in the Praesepe open cluster: a dynamically unevolved mass function?
摘要：
[摘要]在这篇文章中，我们提出了一个光度测量的结果，以确定旧的疏散星团Praesepe的低质量和褐矮星成员（年龄为590[+150][-120]百万年，距离为190[+6.0][-5.8]pc），并使用它来推断它的质量函数，我们与其他集群进行比较。我们对普拉塞普进行了光学（Ic波段）和近红外（J波段和KS波段）光度测量，空间覆盖范围为3.1度^[2]。随着5西格玛检测限Ic=23.4和J=20.0，我们的调查是敏感的对象与质量约0.6至0.05 Msol。Praesepe的质量函数从0.6Msol上升到0.1Msol，然后在~0.1Msol处翻转。观察到的上升与以前的研究得出的质量函数一致，包括基于自行和测光的调查。将我们的质量函数与另一个年龄相近的疏散星团毕星团（年龄约为600 Myr）的质量函数相比较，我们发现了一个显著的差异。可能的原因是，动力蒸发并没有以同样的方式影响毕宿星团和Praesepe，或者这些星团没有相同的初始质量函数，或者动力相互作用改变了一个或两个星团的演化。虽然在集群的二进制分数的差异可能会导致所观察到的（即系统）的质量函数不同，在文献中的测量给出了一个显着的差异，在两个集群的二进制分数的证据。在我们的候选星团中，有六个的质量被预测为等于或低于恒星/亚恒星边界的0.072Msol。
英文摘要：
[Abridged] In this paper, we present the results of a photometric survey to identify low mass and brown dwarf members of the old open cluster Praesepe (age of 590[+150][-120]Myr and distance of 190[+6.0][-5.8]pc) and use this to infer its mass function which we compare with that of other clusters. We have performed an optical (Ic-band) and near-infrared (J and Ks-band) photometric survey of Praesepe with a spatial coverage of 3.1deg^2. With 5sigma detection limits of Ic=23.4 and J=20.0, our survey is sensitive to objects with masses from about 0.6 to 0.05Msol. The mass function of Praesepe rises from 0.6Msol down to 0.1Msol and then turns-over at ~0.1Msol. The rise observed is in agreement with the mass function derived by previous studies, including a survey based on proper motion and photometry. Comparing our mass function with that for another open cluster with a similar age, the Hyades (age ~ 600Myr), we see a significant difference. Possible reasons are that dynamical evaporation has not influenced the Hyades and Praesepe in the same way, or that the clusters did not have the same initial mass function, or that dynamical interactions have modified the evolution of one or both clusters. Although a difference in the binary fractions of the clusters could cause the observed (i.e. system) mass functions to differ, measurements in the literature give no evidence for a significant difference in the binary fractions of the two clusters. Of our cluster candidates, six have masses predicted to be equal to or below the stellar/substellar boundary at 0.072Msol.
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