发表机构
National and Kapodistrian University of Athens; Univ. Grenoble Alpes, CNRS, IPAG; INAF – Osservatorio Astrofisico di Torino（雅典国立卡波蒂斯坦大学; 格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，IPAG; 意大利国家天体物理研究所都灵天文台）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过三维MHD模拟T Tauri星的磁层吸积，明确了稳定与不稳定吸积的判据及相关扭矩公式，应用于观测样本发现多数年轻恒星处于吸积加速状态，其角动量问题仍未解决。
AI 中文摘要
年轻恒星在收缩过程中会通过磁层从周围的原行星盘吸积物质，这两个过程会影响恒星的自转演化。我们研究了稳定和不稳定的吸积 regime（由交换不稳定性导致），并考察了相关的恒星扭矩，以评估年轻恒星的自转演化。我们对倾斜恒星偶极子的圆盘吸积进行了三维MHD模拟，运行了21组模拟，涉及不同的恒星自转速率、偶极场强度、倾角以及质量吸积率。我们发现，当截断半径与共转半径的比值$R_t/R_{co} \gtrsim 0.80-0.85$时，恒星通过稳定 regime 吸积，否则吸积变为不稳定。此外，我们的$R_t/R_{*}$参数化对质量吸积率和偶极强度的依赖性较弱，而对恒星自转速率的依赖性较强。我们推导了影响恒星自转的各流成分的扭矩公式，即吸积、磁层抛射和恒星风。最后，我们将结果应用于一组已测得磁场、质量吸积率和自转周期的年轻恒星样本，发现其中大多数当前应处于不稳定吸积 regime 并经历加速扭矩。我们的研究证实并扩展了之前的结果：不稳定吸积会对中心恒星产生净加速扭矩，而稳定吸积则可能导致恒星自转减速。当将我们的截断半径和扭矩规则应用于观测数据时，我们发现样本中的大多数年轻恒星应处于加速状态，因此年轻恒星的角动量问题仍然存在。
英文摘要
Young stars accrete material from their circumstellar disk through their magnetosphere and undergo contraction; these two processes impact their rotational evolution. We investigate stable and unstable accretion regimes (due to the interchange instability) and examine the associated stellar torques to assess the spin evolution of young stars. We performed 3D MHD simulations of disk accretion onto an inclined stellar dipole. We ran 21 simulations with varying stellar rotation rates, dipole field strengths and obliquities, and mass accretion rates. We find that stars with a ratio of truncation to corotation radius $R_t/R_{co} \gtrsim 0.80-0.85$ accrete via a stable regime, while accretion becomes unstable otherwise. In addition, our $R_t/R_{\ast}$ parametrization weakly depends on the mass accretion rate and the dipolar intensity, while strongly depending on the stellar rotation rate. We derive torque formulae for each flow component affecting the stellar rotation, i.e., accretion, magnetospheric ejections and stellar winds. Finally, we apply our results to a sample of young stars with measured magnetic fields, mass accretion rates, and rotational periods and find that most of them should currently accrete in an unstable regime and undergo spin-up torques. Our study confirms and expands upon previous results. Unstable accretion should lead to a net spin-up torque on the central star, while stable accretion can lead to stellar spin-down. When applying our truncation radius and torque prescriptions to observational data, we find that most young stars in our sample should be in a spin-up state. Thus, the angular momentum problem for young stars remains.
Comments26 pages, 15 figures, accepted for publication in Astronomy & Astrophysics. Updated version with typos corrected following language editing and formatted in the A&A layout
