A complete N-body model of the old open cluster M67
A complete N-body model of the old open cluster M67
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DOI：
10.1111/j.1365-2966.2005.09448.x
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发表时间：
2005-07
影响因子：
4.8
通讯作者：
J. Hurley;O. Pols;S. Aarseth;C. Tout
中科院分区：
文献类型：
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作者：
J. Hurley;O. Pols;S. Aarseth;C. Tout
旧的疏散星团 M67 是当前星团演化模型的理想测试平台，因为它具有动态演化的结构和丰富的恒星种群，显示出恒星、双星和星团演化之间相互作用的明显迹象。在这里，我们提出了 M67 的第一个真正直接的 N 体模型，从零年龄演化到 4 Gyr，充分考虑了星团动力学以及恒星和双星演化。我们的首选模型从 36 000 颗恒星（12 000 颗单星和 12 000 颗双星）开始，总质量接近 19 000 M � ，放置在距银河中心 8.0 kpc 的银河潮汐场中。我们对初始条件和原始二元总体的选择进行了详细解释。在 4 Gyr（M67 的年龄）时，由于质量损失和恒星逃逸，总质量已减少至 2000 Mas。星团中发光恒星的质量和半质量半径与观测结果非常匹配，尽管该模型比观测结果更集中。低质量恒星的优先逃逸使恒星质量和光度函数（LF）显着变平。我们发现 M67 的动态年龄足够大，以至于有关初始质量函数 (IMF) 的信息从当前 LF 和白矮星 (WD) 的当前质量分数中丢失。该模型包含 20 个 4 Gyr 的蓝离散粒子 (BS)，略少于 M67 中观察到的 28 个。九个是二进制文件。蓝色散乱者是通过多种方式形成的，我们发现了在 M67 中观察到的整个品种的形成路径。原始二元种群和动态集群环境在种群塑造中都发挥着重要作用。需要大量的短周期原初双星（周期小于几天）来解释在 M67 中观测到的 BS 数量。三分之二的BS（包括所有在双星系统中发现的）的演化和特性已经被星团动力学改变，而近一半的BS在星团环境之外根本不会形成。另一方面，星团环境也有助于摧毁原始双星群中潜在的BS，因此总数实际上略小于孤立演化相同双星的预期数量。关键词：恒星动力学 - 方法：N 体模拟 - 双星：近距离 - 蓝色落后者 - 恒星：演化 - 疏散星团和关联：一般。
The old open cluster M67 is an ideal testbed for current cluster evolution models because of its dynamically evolved structure and rich stellar populations that show clear signs of interaction between stellar, binary and cluster evolution. Here, we present the first truly direct N-body model for M67, evolved from zero age to 4 Gyr taking full account of cluster dynamics as well as stellar and binary evolution. Our preferred model starts with 36 000 stars (12 000 single stars and 12 000 binaries) and a total mass of nearly 19 000 M � , placed in a Galactic tidal field at 8.0 kpc from the Galactic Centre. Our choices for the initial conditions and for the primordial binary population are explained in detail. At 4 Gyr, the age of M67, the total mass has reduced to 2000 Mas a result of mass loss and stellar escapes. The mass and half-mass radius of luminous stars in the cluster are a good match to observations, although the model is more centrally concentrated than observations indicate. The stellar mass and luminosity functions (LFs) are significantly flattened by preferential escape of low-mass stars. We find that M67 is dynamically old enough that information about the initial mass function (IMF) is lost, both from the current LF and from the current mass fraction in white dwarfs (WDs). The model contains 20 blue stragglers (BSs) at 4 Gyr, which is slightly less than the 28 observed in M67. Nine are in binaries. The blue stragglers were formed by a variety of means and we find formation paths for the whole variety observed in M67. Both the primordial binary population and the dynamical cluster environment play an essential role in shaping the population. A substantial population of short-period primordial binaries (with periods less than a few days) is needed to explain the observed number of BSs in M67. The evolution and properties of two-thirds of the BSs, including all found in binaries, have been altered by cluster dynamics and nearly half would not have formed at all outside the cluster environment. On the other hand, the cluster environment is also instrumental in destroying potential BSs from the primordial binary population, so that the total number is in fact slightly smaller than what would be expected from evolving the same binary stars in isolation. Ke yw ords: stellar dynamics - methods: N-body simulations - binaries: close - blue stragglers - stars: evolution - open clusters and associations: general.