星际氧气分子的气相-尘埃模型研究

本文采用气相-尘埃模型Nautilus研究了星际氧气的演化过程，使用了两种典型初始丰度值下的恒温模型和变化物理条件下的加热模型进行模拟计算. 结果表明，在冷致密云的条件下，CO、O₂和H₂O达到峰值的时间依赖于氢核密度的多少，其随氢核密度的增大而减小. 在加热模型中，在温度升高后的10⁵年后，氧气的丰度值与观测结果符合较好. 在温度大于30 K后，氧气的稳态丰度值将不再随氢核密度而变化，且大于此温度可以阻止氧气大量的沉降到尘埃表面. 此外，无论在恒温模型还是在加热模型中，低氢核密度更有利于O₂的生成.

Gas-Grain Modeling of Interstellar O2

Molecular oxygen (O₂) is essential to human beings on the earth. Although elemental oxygen is rather abundant, O₂ is rare in the interstellar medium. It was only detected in two galactic and one extra-galactic region. The inconsistency between observations and theoretical studies is a big challenge for astrochemical models. Here we report a two-phase modeling research of molecular oxygen, using the Nautilus gas-grain code. We apply the isothermal cold dense models in the interstellar medium with two typical sets of initial elemental abundances, as well as the warm-up models with various physical conditions. Under cold dense conditions, we find that the timescales for gas-phase CO, O₂ and H₂O to reach peak values are dependent on the hydrogen density and are shortened when hydrogen density increases. In warm-up models, O₂ abundances are in good agreement with observations at temperatures rising after 10⁵ yr. In both isothermal and warm-up models, the steady-state O₂ fractional abundance is independent of the hydrogen density, as long as the temperature is high enough (>30 K), at which O₂ is prevented from significant depleting onto grain surface. In addition, low density is preferable for the formation of O₂, whether molecular oxygen is under cold conditions or in warm regions.