A NON-LOCAL THERMODYNAMIC EQUILIBRIUM ANALYSIS OF BORON ABUNDANCES IN METAL-POOR STARS
A NON-LOCAL THERMODYNAMIC EQUILIBRIUM ANALYSIS OF BORON ABUNDANCES IN METAL-POOR STARS
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DOI：
10.1088/0004-637x/713/1/458
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发表时间：
2010-04
期刊：
影响因子：
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通讯作者：
K. Tan;Jian-rong Shi;Gang Zhao
中科院分区：
文献类型：
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作者：
K. Tan;Jian-rong Shi;Gang Zhao
研究了冷星大气中中性硼的非定域热力学平衡线的形成。我们的研究结果证实，NLTE效应的B i共振线，这是由于过度电离和光泵效应的组合，是最重要的热，金属贫乏，低重力的恒星，然而，偏离局部热力学平衡（LTE）的幅度比以前的研究发现的要小。另外，我们的计算结果表明，随着与中性氢碰撞强度的增加，B i的谱线形成将更接近LTE，这与以往的研究结果相反。利用NLTE谱线形成结果，采用HST/GHRS存档谱线合成B i 2497条B共振线的方法，测定了16颗贫金属星的硼丰度。铍和氧的丰度也确定了这些恒星与公布的等效宽度的Be二3131共振和O i 7774三重线，分别。9颗Be和B不贫化的恒星的丰度表明，无论与中性氢的碰撞强度如何，Be和B在对数平面上都随O的增加呈准线性增加，证实了Be和B主要由银河系早期的原初过程产生的结论。这项工作最值得注意的结果是，B与Fe或O以非常相似的速度增加，或者比Be快一点，这与理论模型雅阁。B/Be比值在这里研究的金属丰度范围内几乎保持不变。我们的平均B/Be比福尔斯落在[13 ± 4，17 ± 4]区间内，这与spiral过程的预测相一致。如果贫金属星的11 B/10 B同位素比值与流星值相同，则可能需要ν-过程中的B的贡献。精确测量贫金属恒星中的11B/10 B比率对于了解硼的产生历史至关重要。
The non-local thermodynamic equilibrium (NLTE) line formation of neutral boron in the atmospheres of cool stars are investigated. Our results confirm that NLTE effects for the B i resonance lines, which are due to a combination of overionization and optical pumping effects, are most important for hot, metal-poor, and low-gravity stars; however, the amplitude of departures from local thermodynamic equilibrium (LTE) found by this work is smaller than that of previous studies. In addition, our calculation shows that the line formation of B i will get closer to LTE if the strength of collisions with neutral hydrogen increases, which is contrary to the result of previous studies. The NLTE line formation results are applied to the determination of boron abundances for a sample of 16 metal-poor stars with the method of spectrum synthesis of the B i 2497 Å resonance lines using the archived HST/GHRS spectra. Beryllium and oxygen abundances are also determined for these stars with the published equivalent widths of the Be ii 3131 Å resonance and O i 7774 Å triplet lines, respectively. The abundances of the nine stars which are not depleted in Be or B show that, no matter what the strength of collisions with neutral hydrogen may be, both Be and B increase with O quasilinearly in the logarithmic plane, which confirms the conclusions that Be and B are mainly produced by the primary process in the early Galaxy. The most noteworthy result of this work is that B increases with Fe or O at a very similar speed as, or a bit faster than, Be does, which is in accord with the theoretical models. The B/Be ratios remain almost constant over the metallicity range investigated here. Our average B/Be ratio falls in the interval [13 ± 4, 17 ± 4], which is consistent with the predictions of the spallation process. The contribution of B from the ν-process may be required if the 11B/10B isotopic ratios in metal-poor stars are the same as the meteoric value. An accurate measurement of the 11B/10B ratios in metal-poor stars is crucial to understanding the production history of boron.