An analytical description of the evolution of binary orbital-parameter distributions in N-body computations of star clusters
An analytical description of the evolution of binary orbital-parameter distributions in N-body computations of star clusters
复制标题
星团 N 体计算中双星轨道参数分布演化的分析描述
DOI：
10.1111/j.1365-2966.2011.19257.x
复制
发表时间：
2011
影响因子：
4.8
通讯作者：
Seungkyung Oh
中科院分区：
文献类型：
--
作者：
M. Marks;P. Kroupa;Seungkyung Oh
提出了一种新方法，通过目前最大的现有 N 体模型库来描述星团中最初普遍的双星群的轨道参数分布的演化。结果表明，存在一个恒星动力学算子 M ecl,rh dyn (t)，它在经过一段时间的动力学演化后，根据初始星团质量 Mecl 和半质量半径 rh，唯一地将双星初始 (t = 0) 轨道参数分布函数 Din 转换为新的分布 D M ecl,rh (t)。对于 Din，使用 Kroupa (1995a,b) 导出的分布函数，该函数与前主序列和 I 类二元总体的约束一致。具有较低能量和较高折合质量的二元化合物优先溶解。 - 运算符可用于有效计算和预测星团和整个星系中的二元属性，而无需进一步的 N 体计算。对于当前的 N 体模型集，发现二元群体在交叉时间尺度上改变其属性，使得 M ecl,rh dyn (t) 可以很好地参数化为簇密度 ρecl 的函数。此外，还表明，具有相似初始速度色散的簇中的二元分数遵循相同的演化轨迹，作为经过的弛豫时间数的函数。目前观测到的星团中的双星族对其初始恒星密度 ρecl 施加了限制，发现其范围在 10 2 内。 ρecl(6 rh)/M⊙ pc -3 。疏散星团为 2 × 10 5 ，少数为 10 3 。 ρecl(6 rh)/M⊙ pc -3 。球状星团分别为 10 8 。
A new method is presented to describe the evolution of the orbital-parameter distributions for an initially universal binary population in star clusters by means of the currently largest existing library of N-body models. It is demonstrated that a stellar-dynamical operator, M ecl,rh dyn (t), exists, which uniquely transforms an initial (t = 0) orbital parameter distribution function for binaries, Din, into a new distribution, D M ecl,rh (t), depending on the initial cluster mass, Mecl, and half-mass radius, rh, after some time t of dynamical evolution. For Din the distribution functions derived by Kroupa (1995a,b) are used, which are consistent with constraints for pre-main sequence and Class I binary populations. Binaries with a lower energy and a higher reduced-mass are dissolved preferentially. The -operator can be used to efficiently calculate and predict binary properties in clusters and whole galaxies without the need for further N-body computations. For the present set of N-body models it is found that the binary populations change their properties on a crossing time-scale such that M ecl,rh dyn (t) can be well parametrized as a function of the cluster density, ρecl. Furthermore it is shown that the binary-fraction in clusters with similar initial velocity dispersions follows the same evolutionary tracks as a function of the passed number of relaxation-times. Present-day observed binary populations in star clusters put constraints on their initial stellar densities, ρecl, which are found to be in the range 10 2 . ρecl(6 rh)/M⊙ pc −3 . 2 × 10 5 for open clusters and a few×10 3 . ρecl(6 rh)/M⊙ pc −3 . 10 8 for globular clusters, respectively.