低质量氦星的演化及其对密近双星中电子俘获超新星形成的意义
Evolution of low-mass He stars and implications for electron-capture supernova formation in close binaries
AI总结：
本研究通过详细的恒星与双星演化计算，探究了自转、质量转移等对低质量氦星演化及电子俘获超新星形成的影响，确定了电子俘获超新星的氦星初始质量范围，发现演化结果对初始轨道周期高度敏感，且可通过较大诞生 kick 速度重现多数观测的银河系双中子星系统。
AI中文摘要：
密近双星中带有中子星（NS）伴星的低质量氦（He）星（约2.5至5倍太阳质量）的演化已得到广泛研究，但自转与潮汐相互作用的综合效应仍知之甚少。我们研究自转、质量转移和潮汐相互作用如何影响低质量氦星的演化、电子俘获超新星（ECSNe）的形成以及最终中子星的性质。通过包含质量损失、较差自转和潮汐相互作用的详细恒星与双星演化计算，我们系统探索了导致电子俘获超新星的初始双星参数空间。我们发现自转对低质量氦星演化的影响仅为中等程度；在太阳金属丰度（Z☉）下，电子俘获超新星发生在氦星初始质量2.42至2.67倍太阳质量的狭窄范围内，在0.01倍太阳金属丰度下则为2.37至2.62倍太阳质量。最终形成的中子星自旋周期为7.7至83.8毫秒，磁场约为10^12高斯，旋转能量为2.6×10^48至2.5×10^50尔格，若纳入斯普吕特-泰勒发电机等高效角动量传输机制，这些数值将大幅降低。我们进一步表明，演化结果对初始轨道周期高度敏感，短周期系统会在演化更早阶段经历洛希瓣溢流，并受到更强的双星相互作用。最后，与银河系双中子星系统的比较显示，通过采用相对较大的诞生 kick 速度，可在偏心率-轨道周期平面上重现大多数观测到的双星系统。
英文摘要：
The evolution of low-mass helium (He) stars ($\sim2.5$--$5\,M_\odot$) with neutron-star (NS) companions in close binaries has been extensively studied, but the combined effects of rotation and tidal interaction remain poorly understood. We investigate how rotation, mass transfer, and tidal interactions affect the evolution of low-mass He stars, the formation of electron-capture supernovae (ECSNe), and the properties of the resulting NSs. Using detailed stellar and binary evolution calculations that include mass loss, differential rotation, and tidal interactions, we systematically explore the initial binary parameter space leading to ECSNe. We find that rotation has only a modest effect on the evolution of low-mass He stars. ECSNe occur within a narrow initial He-star mass range of $2.42$--$2.67\,M_\odot$ at solar metallicity ($Z_\odot$) and $2.37$--$2.62\,M_\odot$ at $0.01\,Z_\odot$. The resulting NSs have spin periods of $7.7$--$83.8\,\mathrm{ms}$, magnetic fields of order $10^{12}\,\mathrm{G}$, and rotational energies of $2.6\times10^{48}$--$2.5\times10^{50}\,\mathrm{erg}$, although these values would be substantially reduced if efficient angular-momentum transport mechanisms, such as the Spruit--Tayler dynamo, were included. We further show that the evolutionary outcome is highly sensitive to the initial orbital period, with shorter-period systems undergoing Roche-lobe overflow at earlier evolutionary stages and experiencing stronger binary interactions. Finally, comparison with Galactic double NS systems indicates that most observed binaries can be reproduced in the eccentricity--orbital-period plane by adopting relatively large natal kick velocities.
