我们真的了解尘埃吗？中红外光谱分析方法的系统性与不确定度
Do we really know the dust? Systematics and uncertainties of the mid-infrared spectral analysis methods
摘要：
10微米左右的光谱区域显示出突出的尘埃发射带，通常用于推导原行星尘埃的化学成分。不同的分析方法已经提出了这一目的，但到目前为止，还没有进行比较试验，以测试其有效性。我们用二维辐射转移程序计算了不同几何形状和中心源的圆盘模型的模型谱。这些光谱，然后拟合在一个盲目的测试，使用四种不同的光谱分解方法。我们研究了盘结构（耀斑与平坦），倾角，内部盘孔的大小和恒星光度的拟合的化学成分的影响。我们的研究结果表明，由所有方法导出的粉尘成分偏离系统的真实化学成分。四个测试的光谱分解方法，我们的新的两层温度分布的方法，从输入的灰尘成分和结果显示最弱的系统性影响不同。其他方法所得结果的偏差主要在于它们的假设过于简单（如单一平均晶粒温度或单一组分连续体）。我们还测试了不同噪声水平对谱分解方法结果的影响。我们发现，对于地面观测（8-13微米）的预期不确定性的值的结晶度是约11%的信噪比为100，而空间观测（7-17微米）的不确定性约为5%。在我们的研究结果的基础上，我们提出了一个配方的灰尘光谱数据的分析和解释中红外线，这应该是特别有价值的斯皮策数据和地面红外光谱数据分析在10微米的窗口。
英文摘要：
The spectral region around 10 micrometer, showing prominent dust emission bands, is commonly used to derive the chemical composition of protoplanetary dust. Different analysis methods have been proposed for this purpose, but so far, no comparative test has been performed to test their validity. We calculated model spectra of disk models with different geometries and central sources, using a 2D radiative transfer code. These spectra were then fitted in a blind test using four different spectral decomposition methods. We studied the effect of disk structure (flared vs. flat), inclination angle, size of the inner disk hole and stellar luminosity on the fitted chemical composition. Our results show that the derived dust compositions by all methods deviate systematically from the real chemical composition. Out of the four tested spectral decomposition methods, our new two-layer temperature distribution method, differs the least from the input dust composition and the results show the weakest systematic effects. The reason for the deviations of the results given by other methods lies in their simplifying assumptions (e.g. single average grain temperature or one component continuum). We also tested the influence of different noise levels on the results of the spectral decomposition methods. We find that, for ground-based observations (8-13 micrometer) the expected uncertainty in the value of the crystallinity is about 11% for a signal-to-noise ratio of 100, while for space-based observations (7-17 micrometer) the uncertainty is about 5%. On the basis of our results, we propose a recipe for the analysis and interpretation of dust spectroscopy data in the mid-infrared which should be especially valuable for analysing Spitzer data and ground-based infrared spectroscopy data in the 10 micrometer window.
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