The 69‐μm forsterite band as a dust temperature indicator
The 69‐μm forsterite band as a dust temperature indicator
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69微米镁橄榄石带作为灰尘温度指示器
DOI：
10.1046/j.1365-8711.2002.05349.x
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发表时间：
2002
影响因子：
4.8
通讯作者：
L. Waters
中科院分区：
文献类型：
--
作者：
J. Bowey;M. Barlow;F. Molster;A. Hofmeister;Clare Lee;C. Tucker;T. Lim;P. Ade;L. Waters
在室温（295 K）下，纯晶体镁橄榄石（100%Mg2SiO4）的谱带出现在69.67 μm处;对于Fe含量为10%的橄榄石，相应的谱带出现在73 μm处。富镁镁橄榄石特征在各种ISO LWS光谱中观察到，但相应的富铁橄榄石特征没有。对于我们的样品中的10个天文源，镁橄榄石带的峰值在68.9-69.3 μm范围内，并随着峰值波长的减小而变窄。这与实验室样品冷却至77 K（69.07 μm）和3.5 K（68.84 μm）时观察到的峰向短位移一致。位移峰是由晶格收缩产生的，而锐化是由于在较低温度下声子密度的降低。然而，天文波段比实验室样品窄。通过比较实验室和天文峰值波长，我们推断出我们样本中8个主序后天体的特征镁橄榄石69 μm波段温度在27-84 K范围内。这些数值与使用β=1.5尘埃发射率指数得出的局部连续温度一致，类似于得出的星际不透明度指数值。对于主序前天体HD 100546和MWC 922，69 μm镁橄榄石带的特征温度（分别为127±18和139±10 K）明显高于主序后天体，并且是使用β=1.5推导出的局部连续温度的两倍多。大颗粒（β=0）的假设可以使其中一个天体的69 μm温度与连续谱温度一致，但另一个天体的69 μ m温度与连续谱温度不一致，因此可能暗示了镁橄榄石和连续谱发射颗粒之间的空间分离。μm镁橄榄石谱带作为一种新的特征晶粒温度诊断方法具有很好的应用前景。
A band of pure crystalline forsterite (100 per cent Mg2SiO4) occurs at 69.67 μm at room temperature (295 K); for olivines with ≳10 per cent Fe the corresponding feature is at ≳73 μm. The Mg-rich forsterite feature is observed in a variety of ISO LWS spectra, but the corresponding Fe-rich olivine feature is not. For the 10 astronomical sources in our sample, the forsterite band peaks in the 68.9–69.3 μm range and narrows with decreasing peak wavelength. This is consistent with the shortwards shifting of the peak observed when laboratory samples are cooled to 77 K (69.07 μm) and 3.5 K (68.84 μm). The shifted peak is produced by lattice contraction and the sharpening is due to a decrease in phonon density at lower temperatures. However, the astronomical bands are narrower than those of the laboratory samples. By comparing the laboratory and astronomical peak wavelengths, we deduce characteristic forsterite 69-μm band temperatures that are in the 27–84 K range for the eight post-main-sequence objects in our sample. These values are shown to be consistent with the local continuum temperatures derived using a β=1.5 dust emissivity index, similar to derived interstellar values of the opacity index. For the pre-main sequence-objects HD 100546 and MWC 922, the characteristic 69-μm forsterite band temperatures (127±18 and 139±10 K, respectively) are significantly higher than those of the post-main-sequence objects and are more than twice as high as their local continuum temperatures deduced using β=1.5. The assumption of large grains (β=0) can produce agreement between the derived 69-μm and continuum temperatures for one of these objects but not for the other – a spatial separation between the forsterite and continuum-emitting grains may therefore be implied for it. We conclude that observations of the peak wavelength and FWHM of the 69-μm forsterite band show great promise as a new diagnostic of characteristic grain temperatures.