Coronal mass ejections (CMEs) on stars other than the Sun have proven very difficult to detect. One promising pathway lies in the detection of type II radio bursts. Their appearance and distinctive properties are associated with the development of an outward propagating CME-driven shock. However, dedicated radio searches have not been able to identify these transient features in other stars. Large Alfven speeds and the magnetic suppression of CMEs in active stars have been proposed to render stellar eruptions "radio-quiet". Employing 3D magnetohydrodynamic simulations, we study here the distribution of the coronal Alfven speed, focusing on two cases representative of a young Sun-like star and a mid-activity M-dwarf (Proxima Centauri). These results are compared with a standard solar simulation and used to characterize the shock-prone regions in the stellar corona and wind. Furthermore, using a flux-rope eruption model, we drive realistic CME events within our M-dwarf simulation. We consider eruptions with different energies to probe the regimes of weak and partial CME magnetic confinement. While these CMEs are able to generate shocks in the corona, those are pushed much farther out compared to their solar counterparts. This drastically reduces the resulting type II radio burst frequencies down to the ionospheric cutoff, which impedes their detection with ground-based instrumentation.

中文翻译：

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为恒星日冕物质抛射调整外太空天气无线电

事实证明，太阳以外恒星的日冕物质抛射（CME）非常难以探测。一种有希望的途径在于检测 II 型无线电爆发。它们的外观和独特的特性与向外传播的 CME 驱动的冲击的发展有关。然而，专门的无线电搜索无法识别其他恒星的这些瞬态特征。已经提出大阿尔芬速度和活动恒星中 CME 的磁抑制使恒星爆发“无线电安静”。利用 3D 磁流体动力学模拟，我们在这里研究了日冕 Alfven 速度的分布，重点关注代表年轻的类太阳恒星和中期活动 M 矮星（比邻星）的两个案例。这些结果与标准的太阳模拟进行了比较，并用于表征恒星日冕和风中的易激波区域。此外，使用磁通绳喷发模型，我们在 M 矮星模拟中推动了真实的 CME 事件。我们考虑具有不同能量的喷发来探测弱和部分 CME 磁约束的机制。虽然这些 CME 能够在日冕中产生冲击，但与太阳能对应物相比，它们被推得更远。这极大地降低了由此产生的 II 型无线电爆发频率，降至电离层截止频率，从而阻碍了地面仪器对它们的检测。我们考虑具有不同能量的喷发来探测弱和部分 CME 磁约束的机制。虽然这些 CME 能够在日冕中产生冲击，但与太阳能对应物相比，它们被推得更远。这极大地降低了由此产生的 II 型无线电爆发频率，降至电离层截止频率，从而阻碍了地面仪器对它们的检测。我们考虑具有不同能量的喷发来探测弱和部分 CME 磁约束的机制。虽然这些 CME 能够在日冕中产生冲击，但与太阳能对应物相比，它们被推得更远。这极大地降低了由此产生的 II 型无线电爆发频率，降至电离层截止频率，从而阻碍了地面仪器对它们的检测。