MARCS大气模型中的平衡H₂⁺/H⁻丰度比
Equilibrium \(\mathrm{H}_2^+/\mathrm{H}^-\) Abundance Ratios in MARCS Atmosphere Models
浏览论文内容
中文总结 AI 辅助
本研究基于MARCS大气模型，计算恒星大气中H₂⁺与H⁻的平衡丰度比，发现H₂⁺在约28.4%的分层中丰度超过H⁻，其相对重要性受温度、铁丰度比及分层深度共同影响。
中文摘要 AI 辅助
我们利用紧凑的萨哈型平衡表达式以及MARCS大气模型的分层分压，研究恒星大气中分子氢离子H₂⁺与负氢离子H⁻的平衡丰度比。该分析将温度相关系数比K_{H₂⁺}(T)/K_{H⁻}(T)与完整丰度比区分开来，完整丰度比还取决于局部电离因子N_{H⁺}/N_e；H₂⁺的平衡系数中包含内部配分函数Z_{H₂⁺}(T)。我们处理了51994个MARCS模型，对应2911664个大气分层，直接从列表化的平衡分压计算N(H₂⁺)/N(H⁻)，构建了MARCS网格上该比值的首个系统图谱。在827350个分层中H₂⁺超过H⁻，占所有分析分层的比例F=0.284（即28.4%）。尽管在全局对数平均值中H⁻仍占主导，⟨log₁₀[N(H₂⁺)/N(H⁻)]⟩=-4.229，但在大量分层中H₂⁺的丰度与H⁻相当或更高，其相对重要性随有效温度T_eff升高、铁丰度比[Fe/H]降低及分层加深而增加。因此，该平衡由局部热力学和电离结构共同控制，而非仅由温度决定。这些比值属于平衡丰度诊断，并不意味着不透明度占优；评估不透明度需要依赖波长的截面和辐射转移计算。
英文摘要
We investigate the equilibrium abundance ratio of the molecular hydrogen ion \(\mathrm{H}_2^+\) and the negative hydrogen ion \(\mathrm{H}^-\) in stellar atmospheres using compact Saha-type equilibrium expressions and layer-by-layer partial pressures from MARCS model atmospheres. The analysis distinguishes the temperature-dependent coefficient ratio \(K_{\mathrm{H}_2^+}(T)/K_{\mathrm{H}^-}(T)\) from the full abundance ratio, which also depends on the local ionisation factor \(N_{\mathrm{H}^+}/N_e\). The internal partition function \(Z_{\mathrm{H}_2^+}(T)\) is included in the \(\mathrm{H}_2^+\) equilibrium coefficient. We processed \(51{,}994\) MARCS models, corresponding to \(2{,}911{,}664\) atmospheric layers, and computed \(N(\mathrm{H}_2^+)/N(\mathrm{H}^-)\) directly from the tabulated equilibrium partial pressures, constructing the first systematic map of this ratio across the MARCS grid. \(\mathrm{H}_2^+\) exceeds \(\mathrm{H}^-\) in \(827{,}350\) layers, corresponding to \(F=0.284\), or \(28.4\%\) of all analysed layers. Although \(\mathrm{H}^-\) remains dominant in the global logarithmic mean, with \(\langle \log_{10}[N(\mathrm{H}_2^+)/N(\mathrm{H}^-)] \rangle=-4.229\), \(\mathrm{H}_2^+\) becomes comparable to or more abundant than \(\mathrm{H}^-\) in a substantial subset of layers. Its relative significance increases toward higher \(T_{\mathrm{eff}}\), lower \([\mathrm{Fe}/\mathrm{H}]\), and deeper layers. The balance is therefore controlled by the combined local thermodynamic and ionisation structure, not by temperature alone. These ratios are equilibrium abundance diagnostics and do not imply opacity dominance; assessing opacity requires wavelength-dependent cross-sections and radiative-transfer calculations.
发表机构
- Farabi University（法尔比大学）
- Universidad Nacional Autónoma de México（墨西哥国立自治大学）
- Università di Roma “La Sapienza”（罗马第一大学）
机构由 AI 辅助整理，请以论文原文为准。
