氧的星系演化：三维流体动力学模型大气中的OH线
Galactic Evolution of Oxygen: OH lines in 3D hydrodynamical model atmospheres
摘要：
测量贫金属未演化恒星中的氧线，特别是近紫外OH线，可以提供有关早期银河系性质的宝贵信息。近紫外OH线是获取贫金属矮星氧丰度的重要工具。因此，重要的是要正确地模拟OH线的形成，特别是在贫金属的恒星，其中3D流体动力学模型通常预测较低的温度比平面平行流体静力学模型在上层光球。我们已经利用了52个三维流体动力学模型的大气中使用的代码CO 5 BOLD，从更广泛的CIEST网格计算的矮星网格。这52个模型涵盖了有效温度范围5000- 6500 K，表面重力范围3.5-4.5，金属丰度范围-3<[Fe/H]<0.我们确定了3D-LTE丰度修正在所有52个三维模型的几个OH线和FeI线不同的激发电位。对于较高的温度和表面重力，这些3D-LTE校正通常是负的，达到大约-1 dex的值（对于具有大约1 eV的激发电势的OH 3167）。我们将这些3D-LTE修正应用于个别O丰度，来自OH线，在Israelian等人报道的贫金属矮星样本。(1998，2001）和Boesgaard et al.（1999），通过在3D-LTE校正网格中插值矮星的恒星参数。新的3D-LTE [O/Fe]比仍然保持与1D-LTE类似的趋势，即，朝向较低的[Fe/H]值增加。我们应用1D-NLTE校正三维FeI丰度，我们仍然看到一个增加的[O/Fe]比对较低的金属岩。然而，银河系的[O/Fe]比必须重新审视一旦3D-NLTE校正成为可用的OH和Fe线的3D流体动力学模型大气的网格。
英文摘要：
The measurement of oxygen lines in metal-poor unevolved stars, in particular near-UV OH lines, can provide invaluable information on the properties of the Early Galaxy. Near-UV OH lines constitute an important tool to derive oxygen abundances in metal-poor dwarf stars. Therefore, it is important to correctly model the line formation of OH lines, especially in metal-poor stars, where 3D hydrodynamical models commonly predict cooler temperatures than plane-parallel hydrostatic models in the upper photosphere. We have made use of a grid of 52 3D hydrodynamical model atmospheres for dwarf stars computed using the code CO5BOLD, extracted from the more extended CIFIST grid. The 52 models cover the effective temperature range 5000-6500K, the surface gravity range 3.5-4.5 and the metallicity range -3<[Fe/H]<0. We determine 3D-LTE abundance corrections in all the 52 3D models for several OH lines and FeI lines of different excitation potentials. These 3D-LTE corrections are generally negative reaching values of roughly -1 dex (for the OH 3167 with excitation potential of approximately 1 eV) for the higher temperatures and surface gravities. We apply these 3D-LTE corrections to the individual O abundances, derived from OH lines, of a sample the metal-poor dwarf stars reported in Israelian et al.(1998, 2001) and Boesgaard et al.(1999), by interpolating the stellar parameters of the dwarfs in the grid of 3D-LTE corrections. The new 3D-LTE [O/Fe] ratio still keeps a similar trend as the 1D-LTE, i.e, increasing towards lower [Fe/H] values. We applied 1D-NLTE corrections to 3D FeI abundances and we still see an increasing [O/Fe] ratio towards lower metallicites. However, the Galactic [O/Fe] ratio must be revisited once 3D-NLTE corrections become available for OH and Fe lines for a grid of 3D hydrodynamical model atmospheres.
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