碳化硅的吸收特征：在极端碳星流出物中的尘埃形成
Silicon carbide absorption features: dust formation in the outflows of extreme carbon stars
摘要：
没有可见对应物的红外碳星通常被称为极端碳星。我们已经选择了这些恒星的吸收功能在10-13 $μ$ m范围内，这已暂时归因于碳化硅（SiC）的一个子集。我们添加了三个新的对象，满足这些标准，以前已知的七个，使我们的总样本到十个来源。我们还介绍了这些恒星的辐射转移模拟结果，并与以前的研究结果进行了比较。为了约束模型参数，我们使用已发表的质量损失率，膨胀速度和理论尘埃冷凝模型来确定尘埃冷凝温度。这表明，这些来源的尘埃壳的内部尘埃温度明显高于以前的假设。这也意味着主要的尘埃种类应该是石墨而不是无定形碳。结合更高的冷凝温度，我们表明，这将导致更高的加速度的尘埃颗粒比预期从以前的工作。我们的模型结果表明，非常光学厚的演化阶段与超级风的时间尺度不一致，而是这是一个非常短暂的阶段。此外，我们比较模型和观测参数，试图找到任何相关性。最后，我们表明，光谱的一个来源，IRAS 17534 $-$ 3030，强烈暗示，10-13 $μ$ m功能是由于固态，而不是一个分子物种。
英文摘要：
Infrared carbon stars without visible counterparts are generally known as extreme carbon stars. We have selected a subset of these stars with absorption features in the 10-13 $μ$m range, which has been tentatively attributed to silicon carbide (SiC). We add three new objects meeting these criterion to the seven previously known, bringing our total sample to ten sources. We also present the result of radiative transfer modeling for these stars, comparing these results to those of previous studies. In order to constrain model parameters, we use published mass-loss rates, expansion velocities and theoretical dust condensation models to determine the dust condensation temperature. These show that the inner dust temperatures of the dust shells for these sources are significantly higher than previously assumed. This also implies that the dominant dust species should be graphite instead of amorphous carbon. In combination with the higher condensation temperature we show that this results in a much higher acceleration of the dust grains than would be expected from previous work. Our model results suggest that the very optically thick stage of evolution does not coincide with the timescales for the superwind, but rather, that this is a very short-lived phase. Additionally, we compare model and observational parameters in an attempt to find any correlations. Finally, we show that the spectrum of one source, IRAS 17534$-$3030, strongly implies that the 10-13 $μ$m feature is due to a solid state rather than a molecular species.
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