Close double neutron stars (DNSs) have been observed as Galactic radio pulsars, while their mergers have been detected as gamma-ray bursts and gravitational wave sources. They are believed to have experienced at least one common envelope episode (CEE) during their evolution prior to DNS formation. In the last decades, there have been numerous efforts to understand the details of the common envelope (CE) phase, but its computational modelling remains challenging. We present and discuss the properties of the donor and the binary at the onset of the Roche lobe overflow (RLOF) leading to these CEEs as predicted by rapid binary population synthesis models. These properties can be used as initial conditions for detailed simulations of the CE phase. There are three distinctive populations, classified by the evolutionary stage of the donor at the moment of the onset of the RLOF: giant donors with fully convective envelopes, cool donors with partially convective envelopes, and hot donors with radiative envelopes. We also estimate that, for standard assumptions, tides would not circularise a large fraction of these systems by the onset of RLOF. This makes the study and understanding of eccentric mass-transferring systems relevant for DNS populations.

中文翻译：

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导致双中子星形成的常见包络事件

近距离双中子星 (DNS) 已被观测为银河射电脉冲星，而它们的合并已被探测为伽马射线爆发和引力波源。他们被认为在 DNS 形成之前的进化过程中至少经历了一次共同信封事件 (CEE)。在过去的几十年中，人们为了解公共包络 (CE) 阶段的细节做出了许多努力，但其计算建模仍然具有挑战性。我们提出并讨论了供体和二元在罗氏叶溢出 (RLOF) 开始时的特性，导致这些 CEE，如快速二元种群合成模型所预测的那样。这些属性可用作 CE 阶段详细模拟的初始条件。有三个不同的人群，按 RLOF 开始时供体的演化阶段分类：具有完全对流包膜的巨大供体、具有部分对流包膜的冷供体和具有辐射包膜的热供体。我们还估计，对于标准假设，潮汐不会在 RLOF 开始时循环这些系统的大部分。这使得研究和理解与 DNS 人群相关的偏心传质系统。