论文标题
部分可观测时空混沌系统的无模型预测
WD 1145+017: Alternative models of the atmosphere, dust clouds, and gas rings
论文作者
论文摘要
WD 1145+017是第一个已知通过解体外壳的旋转的白色矮人。它是一个DBZ型白色矮人，具有较大的宽折线线和可变的浅紫外线过渡。已经提出了各种尘埃云和气态环的模型，以解释这种行为。在这里，我们提出了替代模型。为此，对简单的辐射传输代码shellspec进行了修改，并用于测试新的灰尘云和气盘模型。我们使用改进的Tlusty和Synspec代码来计算假设LTE或NLTE的大气模型，并计算恒星的固有光谱。然后，我们使用这些大气模型来估计辐射和对流区域和NLTE光谱合成的质量来估计其化学成分。我们提供了一些（不是全部）浅紫外线过渡的替代解释。这些可能是由尘埃晶粒的光学特性自然引起的：凹陷性和主要是由于正向散射而产生的相位功能。与光学区域相比，后者在紫外线上要强得多，在运输过程中留下了更多的紫外线光子。我们还开发了一种气态磁盘的替代模型，该模型由内部，更热，几乎圆形磁盘以及外部，冷却器和偏心磁盘组成。该结构的预定周期为$ 3.83 \ pm 0.12 $ yr。我们证明，它非常适合观察到的偶色线。这些替代模型解决了可能与以前模型相关的一些缺点，但它们也有自己的缺点。我们确认，大气的化学组成与CI软骨的化学组成相似，但是C，N和S明显不足，并且更接近大块地球组成。这是一个强烈的论点，即该恒星最近遇到了类似地球构图的物质并积聚了材料。
WD 1145+017 is the first white dwarf known to be orbited by disintegrating exoasteroids. It is a DBZ-type white dwarf with strongly variable broad circumstellar lines and variable shallow UV transits. Various models of the dust clouds and gaseous rings have been proposed as an explanation for this behavior. Here we propose alternative models.The simple radiative transfer code Shellspec was modified for this purpose and used for testing the new dust cloud and gas disk models. We used modified TLUSTY and SYNSPEC codes to calculate atmosphere models assuming the LTE or NLTE, and to calculate the intrinsic spectrum of the star. We then used these atmosphere models to estimate the mass of the radiative and convective zones and NLTE spectrum synthesis to estimate their chemical composition. We offer an alternative explanation of some (not all) shallow UV transits. These may be naturally caused by the optical properties of the dust grains: opacities and mainly phase functions as a result of the forward scattering. The latter is much stronger in UV compared to the optical region, leaving more UV photons in the original direction during the transit. We also developed an alternative model of the gaseous disk, consisting of an inner, hotter, and almost circular disk and an outer, cooler, and eccentric disk. The structure precesses with a period of $3.83 \pm 0.12$ yr. We demonstrate that it fits the observed circumstellar lines reasonably well. These alternative models solve a few drawbacks that might be associated with the previous models, but they also have their own disadvantages. We confirm that the chemical composition of the atmosphere is similar to that of CI chondrites but C, N, and S are significantly underabundant and much closer to the bulk Earth composition. This is a strong argument that the star has recently encountered and accreted material from a body of Earth-like composition.
