Kinetic equilibrium of iron in the atmospheres of cool stars - III. The ionization equilibrium of selected reference stars
Kinetic equilibrium of iron in the atmospheres of cool stars - III. The ionization equilibrium of selected reference stars
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DOI：
10.1051/0004-6361:20030907
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发表时间：
2003-06
影响因子：
6.5
通讯作者：
A. Korn;Jianrong Shi;Jianrong Shi;T. Gehren
中科院分区：
文献类型：
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作者：
A. Korn;Jianrong Shi;Jianrong Shi;T. Gehren
为了研究和量化中性氢碰撞的效率，对少数参考恒星进行了非lte线形成计算。使用先前出版物中描述的原子模型，关于氢碰撞的最终判别是基于由费氏/费氏电离平衡确定的表面重力与从希巴谷视差获得的天体测量对应体一致的条件。分析了高信噪比、高分辨率的光谱，以确定单个剖面拟合和铁谱线的差分丰度。根据氢碰撞比例因子S H的选择，我们发现Fei中与LTE的对数丰度偏差范围从0.00 （S H=1）到0.46指数（HD 140283的S H= 0），而Feii遵循LTE。除了Procyon需要进行温和的温度校正以达到电离平衡外，如果将Balmer剖面温度与S H= 3结合，则对金属贫乏的参考恒星获得了极好的一致性。这一数值远远高于从实验室测量和恒星分析推断得出的Li或Ca等简单原子的数值。正确选择碰撞阻尼参数（“范德瓦尔斯”常数）通常比考虑偏离LTE更重要。对于太阳，S H的校准值导致非lte的平均Fei校正0.02指数和Fei对数线（Fe）的平均丰度= 7.49 0.08。我们将推导出的恒星参数与其他作者的类似光谱分析相比较，这些分析也依赖于铁离子平衡作为重力指标。在依巴谷天文测量的基础上，我们的结果被证明比发表的数据集精确一个数量级，无论是在星形和星间散射方面。
Non-LTE line formation calculations of Fei are performed for a small number of reference stars to investigate and quantify the eciency of neutral hydrogen collisions. Using the atomic model that was described in previous publications, the final discrimination with respect to hydrogen collisions is based on the condition that the surface gravities as determined by the Fei/Feii ionization equilibria are in agreement with their astrometric counterparts obtained from Hipparcos parallaxes. High signal-to-noise, high-resolutionspectra are analysed to determine individual profile fits and di erential abundances of iron lines. Depending on the choice of the hydrogen collision scaling factor S H, we find deviations from LTE in Fe i ranging from 0.00 (S H=1 )t o 0.46 dex (S H= 0 for HD 140283) in the logarithmic abundances while Feii follows LTE. With the exception of Procyon, for which a mild temperature correction is needed to fulfil the ionization balance, excellent consistency is obtained for the metal-poor reference stars if Balmer profile temperatures are combined with S H= 3. This value is much higher than what is found for simple atoms like Li or Ca, both from laboratory measurements and inference of stellar analyses. The correct choice of collisional damping parameters ("van-der-Waals" constants) is found to be generally more important for these little evolved metal-poor stars than considering departures from LTE. For the Sun the calibrated value for S H leads to average Fei non-LTE corrections of 0.02 dex and a mean abundance from Fei lines of log"(Fe)= 7.49 0.08. We confront the deduced stellar parameters with comparable spectroscopic analyses by other authors which also rely on the iron ionization equilibrium as a gravity indicator. On the basis of the Hipparcos astrometry our results are shown to be an order of magnitude more precise than published data sets, both in terms of oset and star-to-star scatter.