The Composition Of A Disrupted Extrasolar Planetesimal At SDSS J0845+2257 (Ton 345)
The Composition Of A Disrupted Extrasolar Planetesimal At SDSS J0845+2257 (Ton 345)
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DOI：
10.1093/mnras/stv1201
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发表时间：
2015-05
期刊：
影响因子：
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通讯作者：
David J. Wilson;B. Gaensicke;D. Koester;O. Toloza;A. Pala;E. Breedt;S. Parsons
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文献类型：
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作者：
David J. Wilson;B. Gaensicke;D. Koester;O. Toloza;A. Pala;E. Breedt;S. Parsons
我们对DB白色矮星SDSS J 0845 +2257（Ton 345）进行了详细的研究。利用高分辨率的HST/COS和VLT光谱，我们已经在白色矮星的大气中探测到了氢和11种金属。这些金属的来源几乎可以肯定是来自潮汐破裂的小行星的尘埃和气体碎片的星周盘，其吸积速率为1.6E10 gs^-1。研究吸积物质的化学丰度表明，微行星的组成与地球相似，主要是岩石硅酸盐和金属铁，含水量低。白色矮星对流区内的金属质量相当于一颗直径至少为130-170公里的小行星，尽管碎片盘不断吸积的存在意味着微行星可能比这更大。虽然之前对吸积物质的丰度研究显示，与地球相比，碳的质量分数高得惊人（15%），但我们的独立分析结果表明，碳丰度仅为2.5%。核心物质（铁，镍）的丰度增加表明，吸积物体可能已经失去了一部分地幔，可能是由于恒星风剥离的渐近巨星分支。时间序列光谱揭示了来自轨道气态盘的可变发射，表明SDSS J 0845 +2257的演化行星系统是动态活跃的。
We present a detailed study of the metal-polluted DB white dwarf SDSS J0845+2257 (Ton 345). Using high-resolution HST/COS and VLT spectroscopy, we have detected hydrogen and eleven metals in the atmosphere of the white dwarf. The origin of these metals is almost certainly the circumstellar disc of dusty and gaseous debris from a tidally-disrupted planetesimal, accreting at a rate of 1.6E10 gs^-1. Studying the chemical abundances of the accreted material demonstrates that the planetesimal had a composition similar to the Earth, dominated by rocky silicates and metallic iron, with a low water content. The mass of metals within the convection zone of the white dwarf corresponds to an asteroid of at least ~130-170 km in diameter, although the presence of ongoing accretion from the debris disc implies that the planetesimal was probably larger than this. While a previous abundance study of the accreted material has shown an anomalously high mass fraction of carbon (15 percent) compared to the bulk Earth, our independent analysis results in a carbon abundance of just 2.5 percent. Enhanced abundances of core material (Fe, Ni) suggest that the accreted object may have lost a portion of its mantle, possibly due to stellar wind stripping in the asymptotic giant branch. Time-series spectroscopy reveals variable emission from the orbiting gaseous disc, demonstrating that the evolved planetary system at SDSS J0845+2257 is dynamically active.