质量转移效率极端情况下的双星演化：相接、并合与星族特征
Binary evolution at the extremes of mass-transfer efficiency: Contact, mergers, and population signatures
AI总结：
本研究构建不同质量转移效率的双星演化模型，发现完全保守质量转移会显著提升相接与并合发生率，且无法用单一质量转移效率解释所有观测双星，凸显完善双星模型的必要性。
AI中文摘要：
双星演化本身存在固有不确定性，多个物理过程尚未被充分理解。这些双星物理中的开放问题，叠加了单星演化中的重大不确定性，如角动量输运和内部混合。例如，质量转移（MT）的效率——即被吸积的质量占转移总质量的比例——是双星演化的主要不确定性之一。我们构建了一组一维双星演化模型网格，其初始条件与之前一组受限于吸积星自旋的MT模型网格完全相同；现在我们采用完全保守的MT机制，使得两组网格可进行一对一比较，且覆盖了从高度非保守到完全保守MT的全部范围。我们探究这两种差异极大的MT效率如何改变相接阶段、恒星并合及公共包层阶段的发生概率与发生率，以及它们如何影响当前（后）质量转移双星的星族。我们发现，完全保守MT使相接系统的发生率提升约6倍（从11%升至62%），恒星并合发生率提升超过2倍（从16%升至38%）；还出现了双公共包层（CE）阶段，而该阶段在较低MT效率下不存在。将两组网格构建的合成双星星族与观测到的阿尔戈型（Algol）及剥离恒星双星对比后发现，尽管保守MT更利于解释观测到的剥离恒星双星，但观测到的阿尔戈型双星星族无法用单一MT效率解释。我们得出结论，MT效率取决于双星系统的构型，无法用单一数值描述。本研究凸显了深入理解双星MT的必要性，表明当前恒星双星模型存在不完善之处。
英文摘要：
Binary star evolution remains inherently uncertain, and several physical processes are not well understood. These open questions in binary physics come in addition to major uncertainties in single-star evolution, such as angular momentum transport and interior mixing. For example, the efficiency of mass transfer (MT) -- which is the fraction of transferred mass that is actually accreted -- is one of the main uncertainties in binary evolution. We present a grid of 1D binary evolution models with identical initial conditions to an earlier grid in which MT was limited by the spin-up of the accretors. Now we employ fully conservative MT, allowing for a one-to-one comparison between the two grids, and covering the full range from highly non-conservative to fully conservative MT. We explore how these two maximally different MT efficiencies change the occurrence and incidence of contact phases, stellar mergers and common envelope phases, and how they affect the present-day population of (post-)mass-transferring binaries. We find that fully conservative MT increases the incidence of contact systems by roughly a factor of 6 (from 11% to 62%), and the stellar merger incidence by more than a factor of 2 (from 16% to 38%). We also find the emergence of double-core CE phases, which are absent for lower MT efficiencies. Comparing two synthetic binary populations built using the two grids with observed Algol and stripped-star binaries reveals that even though conservative MT is favoured to reproduce the observed stripped-star binaries, the observed population of Algol binaries cannot be explained by a single MT efficiency. We conclude that the MT efficiency depends on the configuration of binary systems and cannot be described by a single value. Our work highlights the need for a better understanding of binary MT and indicates that current binary-star models are incomplete.
