Dust in the disk winds from young stars as a source of the circumstellar extinction
Dust in the disk winds from young stars as a source of the circumstellar extinction
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盘中的尘埃来自年轻恒星，是星周灭绝的根源
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
V. Grinin
中科院分区：
文献类型：
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作者：
L. Tambovtseva;V. Grinin
我们认为尘埃颗粒生存的问题，从金牛座T和赫比格Ae星的磁盘风。为了我们的分析，我们选择了一个盘风模型，其中风的气体成分通过双极扩散被加热到104 K的温度。我们表明，通过与气体原子碰撞的尘埃颗粒的加热是低效的恒星辐射的加热相比，因此，即使在热风组件的颗粒生存。因此，盘风对紫外线和恒星的光学辐射是不透明的，并且能够吸收相当大的一部分。计算表明，金牛座T星在吸积率为10−8-10− 6 M·yr−1时，被盘风吸收的辐射可以占恒星总光度的20%~ 40%。这意味着金牛座T星的盘风可以起到与当前吸积盘模型中膨胀的内缘相同的作用。在Herbig Ae星中，盘风（r ≤ 0.5 Au）的内层是无尘的，因为这一区域的尘埃在恒星辐射的作用下升华。因此，在这种情况下，被盘风吸收的辐射比例要小得多，只有在吸积率达到或超过10− 6 M yr−1的情况下，才能与膨胀的内边缘的影响相媲美。由于盘风在结构上是不均匀的，它朝向观测者的光学深度是可变的，这应该反映在年轻恒星的光度活动中。出于同样的原因，在高角分辨率的星周盘图像中可以观察到来自气体和尘埃流的螺旋状移动阴影。
We consider the problem of dust grain survival in the disk winds from T Tauri and Herbig Ae stars. For our analysis, we have chosen a disk wind model in which the gas component of the wind is heated through ambipolar diffusion to a temperature of ∼104 K. We show that the heating of dust grains through their collisions with gas atoms is inefficient compared to their heating by stellar radiation and, hence, the grains survive even in the hot wind component. As a result, the disk wind can be opaque to the ultraviolet and optical stellar radiation and is capable of absorbing an appreciable fraction of it. Calculations show that the fraction of the wind-absorbed radiation for T Tauri stars can be from 20 to 40% of the total stellar luminosity at an accretion rate Ṁa = 10−8-10−6M⊙yr−1. This means that the disk winds from T Tauri stars can play the same role as the puffed-up inner rim in current accretion disk models. In Herbig Ae stars, the inner layers of the disk wind (r ≤ 0.5 AU) are dust-free, since the dust in this region sublimates under the effect of stellar radiation. Therefore, the fraction of the radiation absorbed by the disk wind in this case is considerably smaller and can be comparable to the effect from the puffed-up inner rim only at an accretion rate of the order of or higher than 10−6M⊙yr−1. Since the disk wind is structurally inhomogeneous, its optical depth toward the observer can be variable, which should be reflected in the photometric activity of young stars. For the same reason, moving shadows from gas and dust streams with a spiral-like shape can be observed in high-angular-resolution circumstellar disk images.