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arXiv 1001.2146astro-ph.SR
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过渡盘LkCa 15的全二维辐射转移模拟

Full 2D radiative transfer modelling of transitional disk LkCa 15

G. D. Mulders, C. Dominik, M. Min

备注：
5 pages, 4 figures. Published in A&A. v2: changed a reference, adjusted 2 abbreviations.
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摘要：

随着斯皮策的遗产和当前（亚）毫米天文学的进步，已经确定了大量的“过渡”盘，这些盘被认为包含间隙或已经发展出大的内孔，其中一些充满了灰尘。这可能表明，复杂的几何形状可能是一个关键的特点，在磁盘的演变，必须正确理解和建模。LkCa 15周围的圆盘就是这样一个圆盘，其间隙范围为5 - 50 AU，由Espaillat等人（2007年）使用1+1D辐射转移模型确定。为了适应SED，他们提出了两种可能的情况，即内部（<5 AU）盘-光学厚或光学薄-和外部盘的一种情况。我们使用的LkCa 15作为一个展示的间隙盘，以说明在过渡盘的二维辐射转移的重要性，通过显示如何在充满灰尘的内孔的垂直灰尘分布决定不仅径向光学深度，但也外盘的几何形状。我们使用MCMax，一个具有自洽垂直结构的二维辐射转移程序，来模拟SED。我们确定了内外盘的两种可能的几何形状，它们都不同于Espaillat等人（2007）的几何形状。处于流体静力平衡的内盘重新处理足够的星光以适应近红外通量，但也会在外盘的内缘上投射阴影。这就要求外盘刻度高度要足够大，以便从阴影中升起。光学薄的内盘不会投射这样的阴影，并且SED可以配备较小的外盘刻度高度。然而，对于内部区域的尘埃来说，要想变得光学上很薄，刻度高度必须比它的流体静力平衡值大得多，以至于它实际上变成了尘埃壳。目前尚不清楚是否存在可以提供这种配置的物理机制。

英文摘要：

With the legacy of Spitzer and current advances in (sub)mm astronomy, a large number of 'transitional' disks has been identified which are believed to contain gaps or have developped large inner holes, some filled with dust. This may indicate that complex geometries may be a key feature in disk evolution that has to be understood and modeled correctly. The disk around LkCa 15 is such a disk, with a gap ranging from ~5 - 50 AU, as identified by Espaillat et al. (2007) using 1+1D radiative transfer modelling. To fit the SED, they propose 2 possible scenarios for the inner (<5 AU) disk - optically thick or optically thin - and one scenario for the outer disk. We use the gapped disk of LkCa 15 as a showcase to illustrate the importance of 2D radiative transfer in transitional disks, by showing how the vertical dust distribution in dust-filled inner holes determines not only the radial optical depth but also the outer disk geometry. We use MCMax, a 2D radiative transfer code with a self-consistent vertical structure, to model the SED. We identify two possible geometries for the inner and outer disk, that are both different from those in Espaillat et al. (2007). An inner disk in hydrostatic equilibrium reprocesses enough starlight to fit the near infrared flux, but also casts a shadow on the inner rim of the outer disk. This requires the outer disk scale height to be large enough to rise out of the shadow. An optically thin inner disk does not cast such a shadow, and the SED can be fitted with a smaller outer disk scale height. For the dust in the inner regions to become optically thin however, the scale height would have to be so much larger than its hydrostatic equilibrium value that it effectively becomes a dust shell. It is currently unclear if a physical mechanism exists which could provide for such a configuration.

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