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arXiv 1409.6955astro-ph.SR
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冷Ap星HD 24712 II的三维磁性和丰度图。二维磁多普勒成像的全部四个Stokes参数

Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712 II. Two-dimensional Magnetic Doppler Imaging in all four Stokes parameters

N. Rusomarov, O. Kochukhov, T. Ryabchikova, N. Piskunov

摘要:

目的:我们提出了一个磁多普勒成像研究的所有斯托克斯参数的冷,化学奇特的恒星HD 24712。这是首次在分辨率超过10^5的情况下进行此类分析。研究方法:分析的基础上进行的相位分辨观测线轮廓在所有四个斯托克斯参数与HARPSpol仪器连接在3.6米的ESO望远镜。我们使用的磁多普勒成像代码,INVERS10,这使我们能够同时获得的磁场几何形状和表面化学丰度分布。结果如下:我们报告的磁地图HD 24712恢复从FeI,FeII,NdIII,和NaI线强极化信号在所有斯托克斯参数的选择。我们的地磁图成功地再现了观测数据中的大部分细节。我们使用这些磁场图来生成Ca的丰度分布图。这项新的分析表明,HD 24712的表面磁场有一个占主导地位的偶极分量与较弱的贡献,从高阶谐波。Fe和Ca的表面丰度分布显示在磁赤道附近增强,在可见(正)磁极处具有不足的补丁; Nd在正磁极周围高度丰富。Na丰度图显示在负磁极周围有高的过剩。结论:基于我们的调查和类似的最近四个斯托克斯参数磁映射的研究,我们提出了一个初步的证据的假设,即Ap星与偶极类场是老的恒星比有更多的小尺度结构的磁场。我们发现,我们的丰度图是不一致的原子扩散在磁场的存在下,最近的理论计算。

英文摘要:

Aims: We present a magnetic Doppler imaging study from all Stokes parameters of the cool, chemically peculiar star HD 24712. This is the very first such analysis performed at a resolving power exceeding 10^5. Methods: The analysis is performed on the basis of phase-resolved observations of line profiles in all four Stokes parameters obtained with the HARPSpol instrument attached at the 3.6-m ESO telescope. We use the magnetic Doppler imaging code, INVERS10, which allows us to derive the magnetic field geometry and surface chemical abundance distributions simultaneously. Results: We report magnetic maps of HD 24712 recovered from a selection of FeI, FeII, NdIII, and NaI lines with strong polarization signals in all Stokes parameters. Our magnetic maps successfully reproduce most of the details available from our observation data. We used these magnetic field maps to produce abundance distribution map of Ca. This new analysis shows that the surface magnetic field of HD 24712 has a dominant dipolar component with a weak contribution from higher-order harmonics. The surface abundance distributions of Fe and Ca show enhancements near the magnetic equator with an underabundant patch at the visible (positive) magnetic pole; Nd is highly abundant around the positive magnetic pole. The Na abundance map shows a high overabundance around the negative magnetic pole. Conclusions: Based on our investigation and similar recent four Stokes parameter magnetic mapping studies, we present a tentative evidence for the hypothesis that Ap stars with dipole-like fields are older than stars with magnetic fields that have more small-scale structures. We find that our abundance maps are inconsistent with recent theoretical calculations of atomic diffusion in presence of magnetic fields.

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