X-RAY IRRADIATED PROTOPLANETARY DISK ATMOSPHERES. II. PREDICTIONS FROM MODELS IN HYDROSTATIC EQUILIBRIUM
X-RAY IRRADIATED PROTOPLANETARY DISK ATMOSPHERES. II. PREDICTIONS FROM MODELS IN HYDROSTATIC EQUILIBRIUM
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X 射线照射的原行星盘大气。
DOI：
10.1088/0004-637x/699/2/1639
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Ercolano B
中科院分区：
文献类型：
--
作者：
Ercolano B
我们提出了新的星盘X射线光蒸发模型，与前人的结论相反，由此产生的质量损失(主要发生在10-40AU的径向范围内)可能是低质量主序前恒星周围气体的主要扩散机制。我们的模型结合了mocassin蒙特卡罗辐射转移程序和辐照圆盘静水结构的自洽解。我们在假设气体温度等于局部逃逸温度的表面上的声速流出的情况下估计了由此产生的光蒸发率，并推导出∼10−9M☉yr−1的质量损失率，通常比我们以前工作中的相应速率低2-10倍，在我们之前的工作中，我们没有调整辐照磁盘的密度结构。较低的速率，以及质量损失集中在略小的半径的事实，是由于加热的圆盘在几AU处膨胀，这在数十AU处部分屏蔽了圆盘。我们的质量损失通量与Alexander等人的一致。但我们不同于Alexander等人。在我们评估X射线光蒸发的总体意义时，考虑到与X射线驱动的风有关的大圆盘半径(因此发射面积)。另一方面，Gorti和Hollenbach预测的质量损失通量比Alexander等人预测的要低得多。或者我们自己，我们讨论造成这种差异的可能原因。我们强调的事实是，与仅略高于莱曼极限的极紫外线(EUV)光子的光蒸发相比，X射线光蒸发在圆盘扩散方面有两个普遍的优势：年轻恒星即使在失去圆盘后仍有明显的大X射线通量，以及X射线有效地穿透靠近恒星的更大的物质柱。然而，我们强调，我们的X射线驱动的质量损失率比极紫外光蒸发的相应速率(约10−10M☉yr−1)更不确定，这种情况需要通过未来的辐射流体动力学模拟来纠正。
We present new models for the X-ray photoevaporation of circumstellar disks which suggest that the resulting mass loss (occurring mainly over the radial range 10–40 AU) may be the dominant dispersal mechanism for gas around low-mass pre-main-sequence stars, contrary to the conclusions of previous workers. Our models combine use of the mocassin Monte Carlo radiative transfer code and a self-consistent solution of the hydrostatic structure of the irradiated disk. We estimate the resulting photoevaporation rates assuming sonic outflow at the surface where the gas temperature equals the local escape temperature and derive mass-loss rates of∼ 10− 9 M☉ yr− 1, typically a factor of 2–10 times lower than the corresponding rates in our previous work where we did not adjust the density structure of the irradiated disk. The somewhat lower rates, and the fact that mass loss is concentrated toward slightly smaller radii, result from the puffing up of the heated disk at a few AU which partially screens the disk at tens of AU. Our mass-loss fluxes agree with those of Alexander et al. but we differ from Alexander et al. in our assessment of the overall significance of X-ray photoevaporation, given the large disk radii (and hence emitting area) associated with X-ray-driven winds. Gorti & Hollenbach, on the other hand, predict considerably lower mass-loss fluxes than either Alexander et al. or ourselves and we discuss possible reasons for this difference. We highlight the fact that X-ray photoevaporation has two generic advantages for disk dispersal compared with photoevaporation by extreme ultraviolet (EUV) photons that are only modestly beyond the Lyman limit: the demonstrably large X-ray fluxes of young stars even after they have lost their disks and the fact that X-rays are effective at penetrating much larger columns of material close to the star. We however stress that our X-ray-driven mass-loss rates are considerably more uncertain than the corresponding rates for EUV photoevaporation (around 10− 10 M☉ yr− 1) and that this situation will need to be remedied through future radiation hydrodynamical simulations.
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DOI：
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发表时间：
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期刊：
影响因子：
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DOI：
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发表时间：
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