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

在嵌入式原恒星的红外吸收带在7妈妈的波长观察。在这些物体中可以看到带宽的差异。到目前为止，提出了各种材料作为带的起源，即，碳氢化合物、甲醇、CO_2、H_2、NH_3等的光解混合物和碳酸盐。我们再次考察了碳酸盐材料、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谱带，纯MgCO_3和FeCO_3分别在6.83- 6.85 μ m和6.93- 6.94 μ m处出现吸收峰。这些特征与在W33 A中观察到的7 μ m带形非常相似，但是这些碳酸盐在11 μ m附近显示了额外的亚峰，这在原恒星中没有观察到。产物显示出约7 μ m的非常宽的带，其与在Mon R2 #2中观察到的带相匹配。此外，这些材料在11 μ m附近的次峰的峰高都很小。碳酸盐是很好的候选人为7妈妈带的原恒星，虽然他们的光谱有一些额外的频带。

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.