YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppress fluctuations of X-ray emission
YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppress fluctuations of X-ray emission
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YSO 吸积激波：磁、色球或随机流效应可以抑制 X 射线发射的波动
DOI：
10.1051/0004-6361/201321820
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发表时间：
2013
影响因子：
6.5
通讯作者：
G. Peres
中科院分区：
文献类型：
--
作者：
T. Matsakos;T. Matsakos;J. Chièze;C. Stehlé;M. Gonz'alez;L. Ibgui;L. D. Sá;L. D. Sá;T. Lanz;S. Orlando;R. Bonito;R. Bonito;C. Argiroffi;C. Argiroffi;F. Reale;F. Reale;G. Peres;G. Peres
上下文辐射的理论论证和数值模拟
由吸积气体撞击年轻恒星产生的冲击预测准周期性
发射辐射的振荡。然而，观察数据并没有显示出
这样的周期性。目标。我们研究是否物理上合理的扰动，
吸积柱或色球层可能会破坏激波结构，
振荡行为的可观测性。方法.我们进行了局部二维磁流体动力学模拟的一个
吸积激波撞击色球层，产生光学薄辐射损失，
考虑到热传导。我们研究了几种微扰的影响
类型，如在吸积流或色球波动块，也
探索了广泛的血浆β值。结果在弱磁场的情况下，
显示了混沌运动和混合，平滑了扰动，保持了全局
周期性签名另一方面，强磁场将等离子体限制在通量中
管，这导致独立振荡的原纤维的形成。现实
扰动的幅度、长度和时间尺度的值能够
使原纤维振荡异相，抑制纤维振荡的周期性，
排气中结论. YSO中局部均匀磁场的强度
吸积冲击决定了冲击后区域的结构，即，
或者如果它将分裂以形成原纤维的集合。在
在第二种情况下，发现原纤维的大小和形状强烈依赖于
等离子体-β值，但不对扰动类型。因此，实际
原恒星磁场的值预计将在时间中发挥关键作用
可观测发射的依赖性。
Context. Theoretical arguments and numerical simulations of radiative
shocks produced by the impact of the accreting gas onto young stars predict quasi-periodic
oscillations in the emitted radiation. However, observational data do not show evidence of
such periodicity. Aims. We investigate whether physically plausible perturbations in the
accretion column or in the chromosphere could disrupt the shock structure influencing the
observability of the oscillatory behavior. Methods. We performed local 2D magneto-hydrodynamical simulations of an
accretion shock impacting a chromosphere, taking optically thin radiation losses and
thermal conduction into account. We investigated the effects of several perturbation
types, such as clumps in the accretion stream or chromospheric fluctuations, and also
explored a wide range of plasma-β values. Results. In the case of a weak magnetic field, the post-shock region
shows chaotic motion and mixing, smoothing out the perturbations and retaining a global
periodic signature. On the other hand, a strong magnetic field confines the plasma in flux
tubes, which leads to the formation of fibrils that oscillate independently. Realistic
values for the amplitude, length, and time scales of the perturbation are capable of
bringing the fibril oscillations out of phase, suppressing the periodicity of the
emission. Conclusions. The strength of a locally uniform magnetic field in YSO
accretion shocks determines the structure of the post-shock region, namely, whether it
will be somewhat homogeneous or if it will split up to form a collection of fibrils. In
the second case, the size and shape of the fibrils is found to depend strongly on the
plasma-β value but not on the perturbation type. Therefore, the actual
value of the protostellar magnetic field is expected to play a critical role in the time
dependence of the observable emission.