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arXiv 0810.3276astro-ph
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白矮星G 29-38周围的尘埃云。2. 5-40微米的光谱和中红外可变性

The Dust cloud around the White Dwarf G 29-38. 2. Spectrum from 5-40 microns and mid-infrared variability

William T. Reach, Carey Lisse, Ted von Hippel, Fergal Mullally

摘要:

我们使用1-35微米的红外光谱并结合基于彗星和碎片盘光谱研究的各种材料,对白矮星G29-39周围尘埃的矿物学和分布进行了建模。根据对中红外辐射的贡献,G29-38最丰富的矿物是无定形碳、无定形和结晶硅酸盐、水冰和金属硫化物。非晶碳可以等效地被其他具有无特征红外光谱的材料(如金属铁)替代。最适合的结晶硅酸盐是富铁辉石。为了吸收足够的星光来为观测到的辐射提供动力,圆盘必须比恒星半径薄得多(这样它就可以从上面和下面加热),或者它必须有一个大于2度的张开角。质量为2x10^19 g的“中等光学厚度”环面模型与光谱非常吻合。一个物理上薄(小于白矮星半径)且光学上厚的圆盘只能对近红外连续谱做出贡献;这样的圆盘无法解释较长波长的连续谱或强的硅酸盐特征。硅酸盐成分中含有从彗星光谱和陨石中发现的矿物,但富铁辉石比顽火辉石(富镁辉石)或镁橄榄石(富镁橄榄石)在G29-38中更丰富,与大多数彗星或陨石矿物中发现的相反。顽火辉石陨石可能是与G29-38尘埃最相似的太阳系物质。最后,我们建议“热木星”的幸存核心作为碎片的替代(既不是彗星也不是小行星)来源,尽管需要进一步的理论工作来确定这一假设是否可行。

英文摘要:

We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1-35 microns and combining a wide range of materials based on spectral studies of comets and debris disks. In order of their contribution to the mid-infrared emission, the most abundant minerals for G29-38 are amorphous carbon, amorphous and crystalline silicates, water ice, and metal sulfides. The amorphous C can be equivalently replaced by other materials (like metallic Fe) with featureless infrared spectra. The best-fitting crystalline silicate is Fe-rich pyroxene. In order to absorb enough starlight to power the observed emission, the disk must either be much thinner than the stellar radius (so that it can be heated from above and below) or it must have an opening angle wider than 2 degrees. A `moderately optically thick' torus model with mass 2x10^19 g fits the spectrum well. A physically thin (less than the white dwarf radius) and optically thick disk can contribute to the near-infrared continuum only; such a disk cannot explain the longer-wavelength continuum or strong silicate features. The silicate composition contains minerals found from cometary spectra and meteorites, but Fe-rich pyroxene is more abundant than enstatite (Mg-rich pyroxene) or forsterite (Mg-rich olivine) in G29-38, in contrast to what is found in most comet or meteorite mineralogies. Enstatite meteorites may be the most similar solar system materials to the G29-38 dust. Finally, we suggest the surviving core of a `hot jupiter' as an alternative (neither cometary nor asteroidal) origin for the debris, though further theoretical work is needed to determine if this hypothesis is viable.

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