动力学与结构：打破恒星形成中的密度简并
Dynamics versus structure: breaking the density degeneracy in star formation
摘要：
由于“密度简并问题”（density degeneracy problem），单个恒星形成区域（以及行星系统的诞生环境）的初始密度很难被约束：由于两体弛豫，初始密度高的区域比更安静的区域膨胀得更快，因此两个具有相同密度的区域可能有非常不同的初始密度。我们通过从$\mathcal{Q}$参数中折叠关于它们的空间结构的信息，并将结构和现今密度与$N$体模拟的结果进行比较，来约束附近7个恒星形成区域的初始密度。这反过来又对大质量恒星的动力学相互作用和辐射场对多系统和原行星盘的可能影响产生了强烈的限制。我们应用我们的方法来约束这七个区域中的每一个区域的初始二进制人口，并表明只有三个区域的人口-猎户座星云团，$ρ$ Oph和南冕座-与从Kroupa普遍的初始周期分布和二进制分数的统一发展一致。
英文摘要：
The initial density of individual star-forming regions (and by extension the birth environment of planetary systems) is difficult to constrain due to the "density degeneracy problem": an initially dense region expands faster than a more quiescent region due to two-body relaxation and so two regions with the same observed present-day density may have had very different initial densities. We constrain the initial densities of seven nearby star-forming regions by folding in information on their spatial structure from the $\mathcal{Q}$-parameter and comparing the structure and present-day density to the results of $N$-body simulations. This in turn places strong constraints on the possible effects of dynamical interactions and radiation fields from massive stars on multiple systems and protoplanetary discs. We apply our method to constrain the initial binary population in each of these seven regions and show that the populations in only three - the Orion Nebula Cluster, $ρ$ Oph and Corona Australis - are consistent with having evolved from the Kroupa universal initial period distribution and a binary fraction of unity.
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