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arXiv 1105.0973astro-ph.SR
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Ia型超新星喷出物中尘埃的形成

Formation of Dust in the Ejecta of Type Ia Supernovae

Takaya Nozawa, Keiichi Maeda, Takashi Kozasa, Masaomi Tanaka, Ken'ichi Nomoto, Hideyuki Umeda

摘要:

我们研究了Ia型超新星(SNe Ia)的喷出物中尘埃颗粒的形成,采用碳爆燃W7模型。在尘埃形成的计算中,我们应用成核和晶粒生长理论,并考虑两种情况下,有和没有形成CO和SiO分子。计算结果表明,在α_j=1的粘附概率下,C、硅酸盐、Si和FeS颗粒在爆炸后100--300天的早期就能凝聚,而Fe和SiC颗粒基本上不能形成。由于没有H包层的Ia型超新星中气体密度低,新形成晶粒的平均半径通常低于0.01微米,比II-P型超新星中的小得多。这支持了我们先前的结论,即在SNe中,喷出物中形成的尘埃半径较小,包层质量较小。当α j=0.1- 1时,尘埃总质量的范围为3 × 10 ^{-4} M_sun到0.2 M_sun,这取决于是否形成CO和SiO分子。我们还估计了新形成的尘埃的光学厚度和热辐射,并与Ia超新星的相关观测结果进行了比较。我们发现,在超新星Ia的C颗粒的形成被抑制,以符合观测的限制。这意味着高能光子和电子严重抑制了C晶粒的形成效率,或者Ia型超新星最外层的C-O层几乎完全燃烧。最后,我们计算了超新星遗迹中尘埃的破坏过程,发现Ia超新星喷出物中的尘埃颗粒在被注入星际介质之前,几乎完全被冲击气体破坏。这表明超新星Ia不太可能是星际尘埃的主要来源。

英文摘要:

We investigate the formation of dust grains in the ejecta of Type Ia supernovae (SNe Ia), adopting the carbon-deflagration W7 model. In the calculations of dust formation, we apply the nucleation and grain growth theory and consider the two cases with and without formation of CO and SiO molecules. The results of the calculations show that for the sticking probability of alpha_j=1, C, silicate, Si, and FeS grains can condense at early times of ~100--300 days after the explosion, whereas Fe and SiC grains cannot form substantially. Due to the low gas density in SNe Ia with no H-envelope, the average radii of the newly formed grains are generally below 0.01 micron, being much smaller than those in Type II-P SNe. This supports our previous conclusion that the radius of dust formed in the ejecta is smaller in SNe with less massive envelopes. The total dust mass ranges from 3x10^{-4} M_sun to 0.2 M_sun for alpha_j=0.1--1, depending on whether or not CO and SiO molecules are formed. We also estimate the optical depths and thermal emission by the newly formed dust and compare to the relevant observations of SNe Ia. We find that the formation of C grains in SNe Ia is suppressed to be consistent with the observational constraints. This implies that energetic photons and electrons heavily depress the formation efficiency of C grains or that the outermost C-O layer of SNe Ia is almost fully burned. Finally, we perform the calculations of dust destruction in the SN remnants and find that dust grains formed in the ejecta of SNe Ia are almost completely destroyed in the shocked gas before being injected into the interstellar medium. This indicates that SNe Ia are unlikely to be the major sources of interstellar dust.

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