环绕双星盘能否产生壳层燃烧剥离巨星双星的偏心率？
Can circumbinary discs produce the eccentricities of shell-burning stripped giant binaries?
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中文总结 AI 辅助
本研究采用流体动力学模拟方法，发现环绕双星盘与双星的相互作用可解释壳层燃烧剥离巨星双星的观测偏心率分布，需满足偏心率、盘质量及吸积效率等条件，推测这类系统可能均与环绕双星盘发生过相互作用。
中文摘要 AI 辅助
后红巨星（Post-RGB）和后渐近巨星支（Post-AGB）双星统称为壳层燃烧剥离巨星（SBSG）双星，包含一颗近期被剥离包层的主星以及一颗主序伴星。这类系统的特征是存在一个稳定的环绕双星盘（CBD），该盘被认为由质量转移过程中剥离的包层物质形成。它们的偏心率范围在0到0.63之间，这与经典双星演化理论预测的此类质量转移后系统应已圆化的结论相矛盾。我们采用基于流体动力学模拟的新形式主义，研究环绕双星盘-双星相互作用是否能解释观测到的SBSG双星偏心率。为与观测结果对比，我们生成了模型星族，其中质量转移后的偏心率和从环绕双星盘吸积的质量为自由参数。我们发现，当满足以下三个条件时，环绕双星盘-双星相互作用可以重现观测到的SBSG双星偏心率分布：（1）质量转移后的偏心率范围至少达到0.05；（2）环绕双星盘的初始质量至少为0.1倍太阳质量（$M_\bigodot$）；（3）向SBSG星的吸积效率极低，以避免其洛希瓣被重新填满。我们的模型要求质量转移后的偏心率高于经典理论预测值，且环绕双星盘比当前观测到的更大。我们推测存在一类质量转移后的前身系统，其环绕双星盘质量足够大，可驱动显著的偏心率泵浦。质量转移过程中通过L2点的质量损失有待研究，因为这可能形成环绕双星盘并缩短轨道周期，而这对许多稳定形成的SBSG双星而言是必要的。我们假设观测到的偏心率与通过L2点损失的质量相关。由于许多其他相互作用后系统表现出相似的轨道特性，我们推测它们可能都在质量转移后不久与环绕双星盘发生过相互作用。
英文摘要
Post-RGB and post-AGB binaries, collectively shell-burning stripped giant (SBSG) binaries, contain a primary star recently stripped of its envelope, alongside a main-sequence companion. These systems are characterised by a stable circumbinary disc (CBD), thought to have formed from envelope material stripped via mass transfer. Their eccentricities range between $0-0.63$, contradicting canonical binary evolution that predicts such post-mass-transfer systems should have circularised. We investigate whether CBD-binary interaction can explain the observed eccentricities of SBSG binaries using a new formalism based on hydrodynamic simulations. To compare with observations, we generated model populations for which post-mass-transfer eccentricity and amount of mass accreted from the CBD were free parameters. We found that CBD-binary interaction can reproduce the observed eccentricity distribution of SBSG binaries, provided that: (1) their post-mass-transfer eccentricities range up to at least 0.05, (2) their CBDs have initial masses of at least $0.1$ $M_\odot$, and (3) accretion onto the SBSG star is highly inefficient to prevent refilling of its Roche lobe. Our model requires higher post-mass-transfer eccentricities than canonically predicted and more massive CBDs than currently observed. We speculate that there is a population of post-mass-transfer progenitor systems with CBDs massive enough to facilitate significant eccentricity pumping. Mass loss via the $L_2$ point during mass transfer needs investigation, as this could form the CBD and shorten the orbital period, necessary for many SBSG binaries assuming they formed stably. We hypothesise that the observed eccentricities are related to the amount of mass lost via $L_2$. Since many other post-interaction systems exhibit similar orbital properties, we speculate that they may all have interacted with CBDs shortly after mass transfer.
