Abstract

The possibility of solving the problem of a discrepancy in the non-LTE abundances from Ti I and Ti II lines in metal-poor stars is investigated by applying accurate data to take into account the collisions with hydrogen atoms. For this purpose, we have calculated for the first time the rate coefficients for bound–bound transitions in inelastic collisions of titanium atoms and ions with hydrogen atoms and for the following charge-exchange processes: Ti I \(+\) H \(\leftrightarrow\) Ti II \(+\) H\({}^{-}\) and Ti II \(+\) H \(\leftrightarrow\) Ti III \(+\) H\({}^{-}\). The influence of these data on non-LTE abundance determinations has been tested for the Sun and four metal-poor stars. For Ti I and Ti II the application of the derived rate coefficients has led to an increase in the departures from LTE and an increase in the titanium abundance compared to what is obtained using approximate formulas to calculate the rate coefficients. In metal-poor stars we have failed to reconcile the non-LTE abundances from lines of two ionization stages. The problem known in the literature cannot be solved only based on an improvement of the rates of collisions with hydrogen atoms in non-LTE calculations with classical model atmospheres.

中文翻译：

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氢碰撞对冷星中钛丰度测定的影响

摘要

通过应用准确的数据来考虑与氢原子的碰撞，研究了解决贫金属星Ti I和Ti II线中非LTE丰度差异问题的可能性。为此，我们首次计算了钛原子和离子与氢原子的非弹性碰撞中的束缚跃迁的速率系数，以及以下电荷交换过程：Ti I \（+ \） H \（\ leftrightarrow \） Ti II \（+ \） H \（{} ^ {-} \）和Ti II \（+ \） H \（\ leftrightarrow \） Ti III \（+ \） H \（{} ^ { -} \）。这些数据对非LTE丰度确定的影响已针对太阳和四颗贫金属星进行了测试。与使用近似公式计算速率系数所获得的结果相比，对于Ti I和Ti II，所应用的速率系数的应用导致与LTE的距离增加以及钛丰度的增加。在金属贫乏的恒星中，我们未能调和来自两个电离阶段的线路的非LTE丰度。文献中已知的问题不能仅基于使用经典模型大气的非LTE计算中与氢原子的碰撞速率的改善来解决。