扩展吸积盘EUV驱动光致蒸发的经典图像
Broadening the Canonical Picture of EUV-Driven Photoevaporation of Accretion Disks
AI总结：
本文构建考虑光加热和光电离有限时标的解析模型，揭示EUV驱动光致蒸发风比经典图像更广泛的流体力学和热化学状态，并阐明能量效率随EUV强度和谱硬度的变化规律。
摘要：
由氢电离辐射（也称极紫外，EUV）驱动的光致蒸发，深刻塑造了各种天体物理对象的演化。本文主要关注原行星盘的消散，我们构建了一个考虑光加热和光电离有限时标的解析模型。对于给定的EUV发射率和谱硬度，该模型改进了对电离、温度和速度结构随距中心源距离变化的估计。与温度约$10^4{\rm \\,K}$、速度约$10{\rm \\,km\\,s^{-1}}$的完全电离等温风经典图像相比，我们的模型揭示了光致蒸发风更广泛的流体力学和热化学状态。与经典图像不同，对于EUV光度约$10^{30}{\rm \\,erg\\,s^{-1}}$的T~Tauri stars，若谱较软且每次光电离的平均沉积能低于约3.7\\,eV，其电离风呈非等温状态且温度低于经典值。反之，若谱较硬，风在盘的大部分半径处呈原子态且等温。对于较低EUV强度，即使谱较软，通过平流作用也可在$\sim 10{\\, \rm au}$以外形成原子风。我们证明该解析模型的预测与详细的辐射流体力学计算总体一致。模型还阐明了光致蒸发的能量效率如何随EUV照射的强度和谱硬度变化，并解决了文献中关于X射线光致蒸发有效性的分歧。这些发现强调了在建模和解释观测数据时考虑光加热和光电离有限时标的重要性。
英文摘要：
Photoevaporation driven by hydrogen-ionizing radiation, also known as extreme-ultraviolet (EUV), profoundly shapes the lives of diverse astrophysical objects. Focusing here mainly on the dispersal of protoplanetary disks, we construct an analytical model accounting for the finite timescales of photoheating and photoionization. The model offers improved estimates for the ionization, temperature, and velocity structures versus distance from the central source, for a given EUV emission rate and spectral hardness. Compared to the classical picture of fully-ionized and isothermal winds with temperatures $\approx 10^4{\rm \,K}$ and speeds $\approx 10{\rm \,km\,s^{-1}}$, our model unveils broader hydrodynamical and thermochemical states of photoevaporative winds. In contrast to the classical picture, T~Tauri stars with EUV luminosities around $10^{30}{\rm \,erg\,s^{-1}}$ have non-isothermal ionized winds at lower temperatures than the classical value if the spectrum is soft, with an average deposited energy per photoionization less than about 3.7\,eV. Conversely, if the spectrum is hard, the winds tend to be atomic and isothermal at most radii in the disk. For lower EUV intensities, even with soft spectra, atomic winds can emerge beyond $\sim 10{\, \rm au}$ through advection. We demonstrate that the analytical model's predictions are in general agreement with detailed radiation-hydrodynamics calculations. The model furthermore illustrates how the energy efficiency of photoevaporation varies with the intensity and spectral hardness of the EUV illumination, as well as addressing discrepancies in the literature around the effectiveness of X-ray photoevaporation. These findings highlight the importance of considering the finite timescales of photoheating and photoionization, both in modeling and in interpreting observational data.
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