Infrared absorption band at 7 mum of protostar dusts- An explanation with magnesium

在嵌入的原恒星中观察到波长为7 μ m的红外吸收带。在这些物体中可以看到带宽的差异。到目前为止，人们提出了各种各样的物质，如碳氢化合物、甲醇、CO_2、H_2、NH_3等的光解混合物和碳酸盐。我们再次检查了碳酸盐材料、纯碳酸盐以及碳酸盐与氧化物和氢氧化物的混合物的红外吸收带。MgCO_3和FeCO_3的峰值分别为6.83 ~ 6.85和6.93 ~ 6.94。其特征与W33A中观测到的7 μ m波段形状非常相似，但这些碳酸盐在11 μ m附近有额外的亚峰，这是在原恒星中没有观测到的。通过(1)在CO_2气氛中研磨氧化物，(2)在真空条件下加热氢氧化镁，合成了碳酸盐-氧化物-氢氧化镁混合物。结果显示，在7 μ m附近有一个非常宽的波段，这与在Mon R2 #2中观察到的波段相匹配。此外，这些材料在11ma附近的子峰的峰高非常小。主要结果总结如下：碳酸盐虽然在光谱上有一些附加的谱带，但它们是原恒星7母谱带的良好候选者。

An infrared absorption band at a wavelength of 7 mum was observed in embedded protostars. Differences of the band width are seen in these objects. Up to now, various materials are proposed to the origin of the band, i.e., hydrocarbons, methanol, photolyzed mixtures of CO_2, H_2, NH_3 etc, and carbonates. We examined again infrared absorption bands of carbonate materials, pure carbonate, and mixtures of carbonate with oxides and hydroxides.Pure MgCO_3 and FeCO_3 show a peak at 6.83-6.85mum and 6.93-6.94mum, respectively. The features are very similar tothe 7 mum band shape observed in W33A,however these carbonates show additional subpeaks around 11mum region, which have not observed in protostars.We synthesized carbonate-oxide-hydroxide mixtures by (1) grinding oxides in CO_2 atmosphere, and (2) heating of magnesium carbonate hydroxide under vacuum. The products show a very broad band around 7 mum which is matched to the band observed in Mon R2 #2. In addition, the peak height of the subpeaks around 11mum of these materialsare very small.The main result is summarized as follows. Carbonates are good candidates for the 7 mum band of protostars though their spectra have some additional bands.