Title: Weakened Magnetic Braking Signals the Collapse of the Global Stellar Dynamo Show Chinese title

Title: 弱化的磁制动信号表明全球恒星发电机的崩溃

Abstract: Weakened magnetic braking (WMB) was originally proposed in 2016 to explain anomalously rapid rotation in old field stars observed by the Kepler mission. The proximate cause was suggested to be a transition in magnetic morphology from larger to smaller spatial scales. In a series of papers over the past five years, we have collected spectropolarimetric measurements to constrain the large-scale magnetic fields for a sample of stars spanning this transition, including a range of spectral types from late F to early K. During this time, we gradually improved our methods for estimating the wind braking torque in each of our targets, and for evaluating the associated uncertainties. Here, we reanalyze the entire sample with a focus on uniformity for the relevant observational inputs. We supplement the sample with two additional active stars to provide more context for the evolution of wind braking torque with stellar Rossby number (Ro). The results demonstrate unambiguously that standard spin-down models can reproduce the evolution of wind braking torque for active stars, but WMB is required to explain the subsequent abrupt decrease in torque as Ro approaches a critical value for dynamo excitation. This transition is seen in both the large-scale magnetic field and the X-ray luminosity, indicating weakened coronal heating. We interpret these transitions as evidence of a rotational threshold for the influence of Coriolis forces on global convective patterns and the resulting inefficiency of the global stellar dynamo. Show Chinese abstract

Abstract: 弱化磁制动（WMB）最初在2016年被提出，以解释开普勒任务观测到的老年场星中异常快速的旋转现象。 直接原因是磁形态从较大空间尺度向较小空间尺度的转变。 在过去五年的一系列论文中，我们收集了光谱偏振测量数据，以限制跨越这一转变的恒星大尺度磁场，包括从晚F型到早K型的多种光谱类型。在此期间，我们逐步改进了估计每个目标的风制动扭矩的方法，以及评估相关不确定性的方法。 在这里，我们重新分析整个样本，重点关注相关观测输入的统一性。 我们补充了两个额外的活跃恒星，以提供更多关于风制动扭矩随恒星罗西比数（Ro）演化的背景信息。 结果明确表明，标准自转减速模型可以再现活跃恒星风制动扭矩的演化，但需要WMB来解释当Ro接近地磁发电机激发临界值时扭矩随后的突然下降。 这一转变在大尺度磁场和X射线光度中都可以看到，表明日冕加热减弱。 我们将这些转变解释为科里奥利力对全球对流模式的影响的旋转阈值的证据，以及由此产生的全球恒星地磁发电机的低效性。