Model atmospheres of chemically peculiar stars: Self-consistent empirical stratified model of HD24712
Model atmospheres of chemically peculiar stars: Self-consistent empirical stratified model of HD24712
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DOI：
10.1051/0004-6361/200911623
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发表时间：
2009-03
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通讯作者：
D. Shulyak;T. Ryabchikova;L. Mashonkina;O. G. D. O. Astronomy-O.-G.-D.-O.-Astronomy-1405339462;V. University;Austria;I. O. Astronomy;R. Science;Russia.;D. O. Astronomy;S. Physics;Uppsala University;Sweden.
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文献类型：
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作者：
D. Shulyak;T. Ryabchikova;L. Mashonkina;O. G. D. O. Astronomy-O.-G.-D.-O.-Astronomy-1405339462;V. University;Austria;I. O. Astronomy;R. Science;Russia.;D. O. Astronomy;S. Physics;Uppsala University;Sweden.
一些化学性质奇特的恒星的高分辨率光谱清楚地表明，它们的大气层中存在着强烈的丰度梯度。然而，这些不均匀性通常被忽略在模式大气计算的标准方案，制动模式结构和光谱导出的丰度模式之间的一致性。本文提出了roAp星星HD 24712的第一个经验自洽恒星大气模型，该模型包含了化学元素的分层，并且直接从观测到的谱线轮廓导出，而不需要对造成这些异常的物理机制进行耗时的模拟。我们利用LLmodels恒星模式大气程序和DDAFIT最小化工具分析了化学元素层结和自洽大气模式的建立。经验测定的Pr和Nd分层在HD24712的大气中是基于NLTE线形成的Prii/iii和Ndii/iii与使用的ESTIL代码。通过层结分析的迭代过程和模式大气结构的重新计算，构造了一个自洽的HD24712模式，即温压结构与层结分析结果一致的模式。结果表明，分层的化学元素导致相当大的变化，在模型结构相比，非分层均匀的情况下。我们发现，稀土元素的积累允许在星星的高层大气中存在逆温度梯度，最大温度增加约600 K。
High-resolution spectra of some chemically peculiar stars clearly demonstrate the presence of strong abundance gradients in their atmospheres. However, these inhomogeneities are usually ignored in the standard scheme of model atmosphere calculations, braking the consistency between model structure and spectroscopically derived abundance pattern. In this paper we present first empirical self-consistent stellar atmosphere model of roAp star HD24712, with stratification of chemical elements included, and which is derived directly from the observed profiles of spectral lines without time-consuming simulations of physical mechanisms responsible for these anomalies. We used the LLmodels stellar model atmosphere code and DDAFIT minimization tool for analysis of chemical elements stratification and construction of self-consistent atmospheric model. Empirical determination of Pr and Nd stratification in the atmosphere of HD24712 is based on NLTE line formation for Prii/iii and Ndii/iii with the use of the DETAIL code. Based on iterative procedure of stratification analysis and subsequent re-calculation of model atmosphere structure we constructed a self-consistent model of HD24712, i.e. the model which temperature-pressure structure is consistent with results of stratification analysis. It is shown that stratification of chemical elements leads to the considerable changes in model structure as to compare with non-stratified homogeneous case. We find that accumulation of REE elements allows for the inverse temperature gradient to be present in upper atmosphere of the star with the maximum temperature increase of about 600K.