arXiv 2310.019852023-10-03astro-ph.EPastro-ph.HEastro-ph.SR

X射线光蒸发原行星盘风的霍尔磁流体动力学模拟

Hall-magnetohydrodynamic simulations of X-ray photoevaporative protoplanetary disc winds

Eleftheria Sarafidou, Oliver Gressel, Giovanni Picogna, Barbara Ercolano

备注：: 12 pages, 11 figures, to be submitted to MNRAS

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AI总结：

本研究结合非理想磁流体动力学效应与热化学，通过含霍尔效应的二维MHD模拟探究X射线光蒸发原行星盘风，明确了磁场对质量损失率的影响条件与作用机制。

摘要：

理解原行星盘（PPDs）的复杂演化及其通过高能恒星辐射的弥散过程是天体物理学领域的重要挑战。近期研究已证实，中心原恒星发出的X射线辐射可显著加热盘表面，引发强劲的光蒸发风，抛射出盘质量的相当一部分。此外，该领域的最新研究表明，同时考虑非理想磁流体动力学（MHD）效应与详细热化学的全球原行星盘模拟具有重要意义。\n本文的研究动机是结合这两个方面，探究它们如何相互作用。研究重点关注霍尔效应（HE）及其对整体磁场拓扑结构和质量损失/吸积率的影响。我们利用一种新型X射线温度参数化方法，采用NIRVANA流体代码开展包含所有非理想效应的二维轴对称MHD模拟。研究发现，在磁场对齐取向中，霍尔效应会导致极向场线发生显著的向内位移，可通过层流麦克斯韦应力提升吸积率。我们发现外流主要由光蒸发驱动——除非磁场强度足够高（即βₚ≤10³）或X射线光度足够低（即logL_X≤29.3）。推断得到的质量损失率处于10⁻⁸至10⁻⁷M⊙yr⁻¹的预期范围内。作为对比，我们还开展了纯流体动力学（HD）模拟，并将其与等效的MHD模拟结果进行比较。结果发现，磁场确实对质量损失率有贡献，但仅在L_X足够低（即logL_X≤30.8）时才可明显观测到。对于高于该值的情况，MHD模型预测的风质量损失率与纯HD模型的预测结果趋于一致。

英文摘要：

Understanding the complex evolution of protoplanetary disks (PPDs) and their dispersal via energetic stellar radiation are prominent challenges in astrophysics. It has recently been established that specifically the X-ray luminosity from the central protostar can significantly heat the surface of the disk, causing powerful photoevaporative winds that eject a considerable fraction of the disc's mass. Recent work in the field has moreover shown the importance of global PPD simulations that simultaneously take into account non-ideal magnetohydrodynamic (MHD) effects and detailed thermochemistry. Our motivation with the current paper lies in combining these two aspects and figure out how they interact. Focus is put on the Hall Effect (HE) and the impact it has on the overall field topology and mass loss/accretion rates. Utilizing a novel X-ray temperature parametrisation, we perform 2D-axisymmetric MHD simulations with the NIRVANA fluid code, covering all non-ideal effects. We find that, in the aligned orientation, the HE causes prominent inward displacement of the poloidal field lines that can increase the accretion rate through a laminar Maxwell stress. We find that outflows are mainly driven by photoevaporation -- unless the magnetic field strength is considerable (i.e., $β_p\leq 10^{3}$) or the X-ray luminosity low enough (i.e., $\log{L_X}\leq 29.3$). Inferred mass loss rate are in the range of the expected values $10^{-8}$ to $10^{-7}M_{\odot}yr^{-1}$. For comparison, we have also performed pure hydrodynamic (HD) runs and compared them with the equivalent MHD runs. Here we have found that the magnetic field does indeed contribute to the mass loss rate, albeit only discernibly so for low enough $L_X$ (i.e., $\log{L_X}\leq 30.8$). For values higher than that, the wind mass loss predicted from the MHD set converges to the ones predicted from pure HD.

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