arXiv 2009.123362020-09-25astro-ph.SR

磁早期B型星IV：爆发还是泄漏？H $α$发射作为离心磁层中等离子体输运的诊断

The Magnetic Early B-type Stars IV: Breakout or Leakage? H$α$ emission as a diagnostic of plasma transport in centrifugal magnetospheres

M. E. Shultz, S. Owocki, Th. Rivinius, G. A. Wade, C. Neiner, E. Alecian, O. Kochukhov, D. Bohlender, A. ud-Doula, J. D. Landstreet, J. Sikora, A. David-Uraz, V… 展开作者

M. E. Shultz, S. Owocki, Th. Rivinius, G. A. Wade, C. Neiner, E. Alecian, O. Kochukhov, D. Bohlender, A. ud-Doula, J. D. Landstreet, J. Sikora, A. David-Uraz, V. Petit, P. Cerrahoğlu, R. Fine, G. Henson, the MiMeS, BinaMIcS Collaborations

备注：: 33 pages, 26 figures, 2 tables, accepted for publication in MNRAS
DOI：: 10.1093/mnras/staa3102

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摘要：

具有强磁场的快速旋转的早型恒星经常显示出源自离心磁层（CM）的H $α$发射，离心磁层是一种星周结构，在这种结构中，由于磁约束等离子体的磁强制共转而产生的离心支持使其能够积累到高密度。目前尚不清楚CM血浆是否通过离心分离器（CB）或未识别的泄漏机制逸出。我们已经进行了第一次全面检查的H $α$目前已知的所有恒星显示CM模式发射的发射特性。我们发现，发射的开始主要取决于CM的面积，这可以简单地预测的值$B_{\rm K}$的磁场在开普勒共转半径$R_{\rm K}$。发射强度对CM面积和$B_{\rm K}$都非常敏感。发射起始和强度{ \em not}取决于有效温度、光度或质量损失率。这些结果都有利于CB场景，然而，在任何CM诊断中缺乏内在的可变性表明CB必须是一个基本上连续的过程，即它有效地充当泄漏机制。我们还表明，发射轮廓形状是近似的尺度不变，即\它们在很大范围的发射强度和恒星参数上大致相似。虽然最大发射半径与预期的$R_{\rm K}$密切相关，但它总是更大，与预测发射应在$R_{\rm K}$达到峰值的模型相矛盾。

英文摘要：

Rapidly rotating early-type stars with strong magnetic fields frequently show H$α$ emission originating in Centrifugal Magnetospheres (CMs), circumstellar structures in which centrifugal support due to magnetically enforced corotation of the magnetically confined plasma enables it to accumulate to high densities. It is not currently known whether the CM plasma escapes via Centrifugal Breakout (CB), or by an unidentified leakage mechanism. We have conducted the first comprehensive examination of the H$α$ emission properties of all stars currently known to display CM-pattern emission. We find that the onset of emission is dependent primarily on the area of the CM, which can be predicted simply by the value $B_{\rm K}$ of the magnetic field at the Kepler corotation radius $R_{\rm K}$. Emission strength is strongly sensitive to both CM area and $B_{\rm K}$. Emission onset and strength are {\em not} dependent on effective temperature, luminosity, or mass-loss rate. These results all favour a CB scenario, however the lack of intrinsic variability in any CM diagnostics indicates that CB must be an essentially continuous process, i.e.\ it effectively acts as a leakage mechanism. We also show that the emission profile shapes are approximately scale-invariant, i.e.\ they are broadly similar across a wide range of emission strengths and stellar parameters. While the radius of maximum emission correlates closely as expected to $R_{\rm K}$, it is always larger, contradicting models that predict that emission should peak at $R_{\rm K}$.

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