We determined astrophysical and dynamical parameters of the open clusters (OCs) NGC 2587, Collinder 268 (Col 268), Melotte 72 (Mel 72), and Pismis 7 from Gaia DR2 photometric/astrometric data and a new technique, fitCMD. fitCMD provides (Z, Age(Gyr)) as (0.025, 0.45) for NGC 2587, (0.0025, 0.5) for Col 268, (0.011, 1.25) for Mel 72, and (0.008, 1.00) for Pismis 7, respectively. As compared to Gaia DR2 distances, the obtained photometric distances from fitCMD provide somewhat close distances. For NGC 2587 and Mel 72, both distances are in good concordance. Except for NGC 2587, the ages of the remaining OCs are higher than their relaxation times, which suggests that they are dynamically relaxed. NGC 2587 did not undergo dynamical evolution. Mel 72 and Pismis 7 with relatively flat MF slopes indicate signs of a somewhat advanced dynamical evolution, in the sense that they appear to have lost a significant fraction of their low-mass stars to the field. Pismis 7's negative/flat mass function slope indicates that its high mass stars slightly outnumber its low mass ones. Given its mild dynamical evolution, the high mass stars move toward the central region, while low-mass stars are continually being lost to the field. Col 268 presents small dimensions, which suggest a primordial origin. The outer parts of Mel 72 and Pismis 7—with large cluster radii expand with time, while Mel 72's core contracts because of dynamical relaxation.

中文翻译：

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疏散星团的天体物理参数和动力学演化：NGC 2587、Collinder 268 和 Melotte 72、Pismis 7

我们从 Gaia DR2 光度/天体测量数据和新技术fitCMD确定了疏散星团 (OC) NGC 2587、Collinder 268 (Col 268)、Melotte 72 (Mel 72) 和 Pismis 7 的天体物理和动力学参数。fitCMD提供的 (Z, Age(Gyr)) 分别为 NGC 2587 的 (0.025, 0.45)、Col 268 的 (0.0025, 0.5)、Mel 72 的 (0.011, 1.25) 和 Pismis 7 的 (0.008, 1.00)。与 Gaia DR2 距离相比，从fitCMD获得的光度距离提供稍近的距离。对于 NGC 2587 和 Mel 72，两个距离都具有良好的一致性。除 NGC 2587 外，其余 OC 的年龄均高于弛豫时间，表明它们处于动态弛豫状态。NGC 2587 没有经历动力演化。Mel 72 和 Pismis 7 的 MF 斜率相对平坦，这表明它们有一些先进的动力学演化迹象，从某种意义上说，它们似乎已经失去了大部分低质量恒星。Pismis 7 的负/平坦质量函数斜率表明其高质量恒星的数量略多于其低质量恒星。鉴于其温和的动力学演化，大质量恒星向中心区域移动，而低质量恒星则不断地消失在磁场中。Col 268 呈现出小尺寸，这表明它是原始起源。