三维非理想MHD风驱动盘中的罗斯贝波不稳定性与子结构形成
Rossby Wave Instability and Substructure Formation in 3D Non-Ideal MHD Wind-Launching Disks
AI总结：
本研究通过非理想MHD数值模拟发现，风驱动原行星盘中的气体环间隙结构会因罗斯贝波不稳定性形成两类涡旋，虽不破坏环隙结构，但为解释非轴对称尘埃特征提供了新可能。
摘要：
环和间隙在原行星盘（PPDs）的尘埃连续谱辐射中被常规观测到，它们的形成与演化机制仍存在争议。已有研究表明，风驱动盘中存在自发形成气体环与间隙的可能性。本文通过数值模拟证明，这类气体子结构会受到罗斯贝波不稳定性（RWI）的影响而失稳。具体而言，短波长方位角模式发展更早，长波长模式后期占据主导，在环中形成拉长的（弧状）反气旋涡，在间隙中形成（强磁化的）气旋涡，这些涡旋持续存在至模拟结束。与流体力学情形不同，在我们的非理想MHD模拟中，纵横比达到10及以上的高度拉长涡旋会随时间衰减。这种差异可能由磁致运动导致，尤其是具有大方位角涡度分量的强经向环流，其可能与涡旋偏好的柱状结构不相容。气旋与反气旋RWI涡旋会饱和在中等水平，会改变但不会破坏盘径向气体分布中的环与间隙。特别是，它们不会切断低密度区的极向磁通量累积，也不会破坏对风驱动盘的环与间隙形成至关重要的特征经向流模式。尽管如此，RWI及其相关涡旋为通过非理想MHD解释小部分原行星盘中观测到的非轴对称尘埃特征提供了可能性，不过还需要详细的尘埃处理来探究这一可能性。
英文摘要：
Rings and gaps are routinely observed in the dust continuum emission of protoplanetary discs (PPDs). How they form and evolve remains debated. Previous studies have demonstrated the possibility of spontaneous gas rings and gaps formation in wind-launching disks. Here, we show that such gas substructures are unstable to the Rossby Wave Instability (RWI) through numerical simulations. Specifically, shorter wavelength azimuthal modes develop earlier, and longer wavelength ones dominate later, forming elongated (arc-like) anti-cyclonic vortices in the rings and (strongly magnetized) cyclonic vortices in the gaps that persist until the end of the simulation. Highly elongated vortices with aspect ratios of 10 or more are found to decay with time in our non-ideal MHD simulation, in contrast with the hydro case. This difference could be caused by magnetically induced motions, particularly strong meridional circulations with large values of the azimuthal component of the vorticity, which may be incompatible with the columnar structure preferred by vortices. The cyclonic and anti-cyclonic RWI vortices saturate at moderate levels, modifying but not destroying the rings and gaps in the radial gas distribution of the disk. In particular, they do not shut off the poloidal magnetic flux accumulation in low-density regions and the characteristic meridional flow patterns that are crucial to the ring and gap formation in wind-launching disks. Nevertheless, the RWI and their associated vortices open up the possibility of producing non-axisymmetric dust features observed in a small fraction of protoplanetary disks through non-ideal MHD, although detailed dust treatment is needed to explore this possibility.
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