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arXiv 1107.2071astro-ph.EP
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Spitzer Space Telescope对73 P/Schwassmann-Wachmann 3彗星的红外光谱研究

Infrared Spectroscopy of Comet 73P/Schwassmann-Wachmann 3 using the Spitzer Space Telescope

Michael L. Sitko, Carey M. Lisse, Michael S. Kelley, Elisha F. Polomski, David K. Lynch, Ray W. Russell, Robin L. Kimes, Barbara A. Whitney, Michael J. Wolff, David E. Harker

备注：
70 pages, 21 figures, accepted for publication in AJ
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摘要：

我们用斯皮策空间望远镜红外光谱仪（IRS）观测了73 P/Schwassmann-Wachmann 3（SW 3）彗星的5-37微米热辐射，即B和C组分。我们获得了整个波长间隔的低光谱分辨率（R ~ 100）数据，以及16和22微米的图像。这些观测提供了一个前所未有的机会来研究来自表面的几乎原始的物质，以及直到最近的黄道彗星的内部-彗星表面只经历了两次近日点，并且包括完全新鲜的物质。使用各种矿物类型，包括无定形和结晶组分的光谱建模。我们发现，硅酸盐结晶度，约35%，比大多数其他彗星具有较强的发射功能，而其丰富的无定形碳较高。两者都表明，SW 3是迄今为止被详细研究过的化学性质最原始的太阳系天体之一，而且它比迄今为止研究过的大部分彗星形成得更早，或者离太阳更远。这两个碎片的相似尘埃成分表明，它们在矿物学上不是异质的，而是在其体积上均匀一致的。来自光谱模型的原子丰度表明O的消耗相比，太阳光球值，尽管包括水冰和气体的模型。原子碳可能是太阳能或略低于太阳能，但它的丰度是复杂的光谱无特征的矿物物种的光谱的一部分，最敏感的C丰度的derication的潜在贡献。我们发现了一个相对较高的热辐射，约0.13的尘埃，考虑到大量的黑暗碳质材料，但与丰富的小颗粒和强发射功能的存在一致。

英文摘要：

We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 micron thermal emission of comet 73P/Schwassmann-Wachmann 3 (SW3), components B and C. We obtained low spectral resolution (R ~ 100) data over the entire wavelength interval, along with images at 16 and 22 micron. These observations provided an unprecedented opportunity to study nearly pristine material from the surface and what was until recently the interior of an ecliptic comet - cometary surface having experienced only two prior perihelion passages, and including material that was totally fresh. The spectra were modeled using a variety of mineral types including both amorphous and crystalline components. We find that the degree of silicate crystallinity, ~ 35%, is somewhat lower than most other comets with strong emission features, while its abundance of amorphous carbon is higher. Both suggest that SW3 is among the most chemically primitive solar system objects yet studied in detail, and that it formed earlier or farther from the sun than the bulk of the comets studied so far. The similar dust compositions of the two fragments suggests that these are not mineralogically heterogeneous, but rather uniform throughout their volumes. Atomic abundances derived from the spectral models indicates a depletion of O compared to solar photospheric values, despite the inclusion of water ice and gas in the models. Atomic C may be solar or slightly sub-solar, but its abundance is complicated by the potential contribution of spectrally featureless mineral species to the portion of the spectra most sensitive to the derication of the C abundance. We find a relatively high bolometric albedo, ~ 0.13 for the dust, considering the large amount of dark carbonaceous material, but consistent with the presence of abundant small particles and strong emission features.

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