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arXiv 2602.04995astro-ph.SRastro-ph.GA
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致密氢化学平衡与Gaia低质量问题在低温白矮星中

Complex hydrogen chemical equilibrium and Gaia low mass problem in cool white dwarfs

Institute of Energy Technologies - Theory and Computation of Energy Materials (IET-3), Forschungszentrum Jülich GmbH（于利希研究中心能源技术研究所-能源材料理论与计算）；Jülich Aachen Research Alliance JARA Energy & Center for Simulation and Data Science (CSD)（于利希亚琛研究联盟JARA能源与数据模拟中心）

Piotr M. Kowalski

备注：
Accepted for publication in Astronomy & Astrophysics
发表信息：
A&A 708, A26 (2026)
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AI总结：

研究揭示低温白矮星中氢化学平衡问题，通过抑制H3+物种形成，修正模型与观测的不一致，提高质量估计精度。

摘要：

大规模Gaia数据集显示，对于有效温度T_eff<6000 K的低温白矮星，模型与观测存在显著偏差，导致这些恒星质量严重低估。本文通过应用最新大气模型和量子力学计算，分析Gaia DR3样本及不同氢物种的形成与稳定性。通过人工抑制H3+物种的形成，显著改变T_eff<6000 K时的化学平衡，导致自由电子和H^-过量，增强H^-的束缚自由吸收。去除H3+物种的化学平衡考虑，使氢原子电离成为自由电子的主要来源，使模型能良好再现Gaia白矮星冷却分支。由于H3+必须在考虑条件下形成，可能当前模型中H3+的配分函数高估或形成H3^-或其他阴离子物种，抑制了H^-作为H3+的反电荷的形成。低温氢大气白矮星的化学平衡必须重新考虑H3+物种的丰度和未计电荷物种的可能存在。

英文摘要：

Large Gaia data set shows substantial misfit between models and observation for cool white dwarfs with $T_{\rm eff}<6000\,\rm K$, resulting in severe underestimation of masses of these stars. We aim to understand the underlying modelling issues. State of the art atmosphere models have been applied to analyse the Gaia DR3 sample of white dwarfs as well as quantum mechanical calculations to quantify formation and stability of different hydrogen species in the atmospheres of these stars. We reconcile the models and observations when we artificially suppress formation of $\rm H_3^+$ species, a process which substantially alters the chemical equilibrium at $T_{\rm eff}<6000\,\rm K$, resulting in an overabundance of free electrons and $\rm H^-$, and strengthening of $\rm H^-$ bound-free absorption. Removing the $\rm H_3^+$ species from chemical equilibrium consideration makes ionization of hydrogen atoms the main source of free electrons, with the resulting models reproducing well the Gaia white dwarfs cooling branch. Because $\rm H_3^+$ must form under the considered conditions, likely it is the overestimation of its partition function and resulting abundance or the formation of $\rm H_3^-$ or another anionic species that suppresses the formation of $\rm H^-$ as a countercharge for $\rm H_3^+$ in current models. Chemical equilibrium in cool, hydrogen atmospheres white dwarfs must be reconsidered in respect to the abundance of $\rm H_3^+$ species and presence of unaccounted charge species.

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