Non-LTE models for the gaseous metal component of circumstellar discs around white dwarfs
Non-LTE models for the gaseous metal component of circumstellar discs around white dwarfs
复制标题
白矮星周围星周盘气态金属成分的非 LTE 模型
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
Klaus Werner
中科院分区：
文献类型：
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作者：
S. Hartmann;Thorsten Nagel;T. Rauch;Klaus Werner
语境。最近在单个白矮星周围发现了气态金属盘。人们认为它们是由破碎的行星体发展而来的。目标。光谱分析将使我们能够研究太阳系外行星物质的成分。我们详细研究了第一个发现气盘的物体（SDSS J122859.93+104032.9）。方法。我们通过计算详细的垂直结构和线谱来对粘性气体盘进行非 LTE 建模。这些模型由碳、氧、镁、硅、钙和氢组成，其化学丰度是太阳系小行星的典型化学丰度。根据流体动力学模拟的建议，通过假设旋臂和偏心盘结构来对线不对称性进行建模。结果。观察到的红外Ca ii 发射三重态可以用位于潮汐破坏半径内部的贫氢金属气盘来模拟，Teff ≈ 6000 K，表面质量密度为Σ ≈ 0.3 g/cm 2 。内半径被很好地限制在大约 0.64 R� 。线轮廓不对称性可以通过旋臂结构或偏心盘来再现，后者因其时间变化行为而受到青睐。这种结构的质量达到 0.64 到 1.5 R�，质量约为 3−6 × 10 21 g，后者相当于一颗直径 135 公里的太阳系小行星的质量。
Context. Gaseous metal discs around single white dwarfs have been discovered recently. They are thought to develop from disrupted planetary bodies. Aims. Spectroscopic analyses will allow us to study the composition of extrasolar planetary material. We investigate in detail the first object for which a gas disc was discovered (SDSS J122859.93+104032.9). Methods. We perform non-LTE modelling of viscous gas discs by computing the detailed vertical structure and line spectra. The models are composed of carbon, oxygen, magnesium, silicon, calcium, and hydrogen with chemical abundances typical for Solar System asteroids. Line asymmetries are modelled by assuming spiral-arm and eccentric disc structures as suggested by hydrodynamical simulations. Results. The observed infrared Ca ii emission triplet can be modelled with a hydrogen-deficient metal gas disc located inside of the tidal disruption radius, with Teff ≈ 6000 K and a surface mass density of Σ ≈ 0.3 g/cm 2 . The inner radius is well constrained at about 0.64 R� . The line profile asymmetry can be reproduced by either a spiral-arm structure or an eccentric disc, the latter being favoured by its time variability behaviour. Such structures, reaching from 0.64 to 1.5 R� , contain a mass of about 3−6 × 10 21 g, the latter equivalent to the mass of a 135-km diameter Solar System asteroid.