M矮星的比较高分辨率光谱学--探索非LTE效应
Comparative high-resolution spectroscopy of M dwarfs -- exploring non-LTE effects
摘要：
M矮星是高分辨率光谱分析的关键目标，因为这些恒星在太阳附近的高入射率和它们作为系外行星宿主的重要性。一些方法上的挑战使这种分析变得困难，导致公布的结果出现重大差异。我们比较M矮参数来自最近的高分辨率近红外研究彼此和基本恒星参数。我们还评估在何种程度上偏离当地热力学平衡（LTE）的Fe和K影响这些研究的结果。我们进行线形成计算的基础上，现代模型的大气网格，以及一个合成的光谱合成代码，处理形成的原子和分子线在冷星大气中，包括偏离LTE。我们使用近红外光谱收集的CRIRES仪器在ESO VLT作为参考观测数据。我们发现，不同的研究得到的有效温度大多同意优于100 K。我们在表面重力和金属丰度上看到了更差的一致性。我们表明，非LTE的影响是可以忽略不计的Fe I在M-矮星大气，但K I是重要的。这些影响，导致K丰度和金属丰度修正的顺序为0.2德克斯，可能是负责一些差异在已发表的分析。大气模型的温度-压力结构的差异可能是造成差异的另一个因素，特别是在低金属含量和高有效温度下。在M矮星的高分辨率光谱研究中，除了输入原子和分子数据外，还应注意谱线形成物理的细节。收集基准M矮星的高质量、宽波长覆盖光谱是未来必不可少的一步。
英文摘要：
M dwarfs are key targets for high-resolution spectroscopic analyses due to a high incidence of these stars in the solar neighbourhood and their importance as exoplanetary hosts. Several methodological challenges make such analyses difficult, leading to significant discrepancies in the published results. We compare M dwarf parameters derived by recent high-resolution near-infrared studies with each other and with fundamental stellar parameters. We also assess to what extent deviations from local thermodynamic equilibrium (LTE) for Fe and K influence the outcome of these studies. We carry out line formation calculations based on a modern model atmosphere grid along with a synthetic spectrum synthesis code that treats formation of atomic and molecular lines in cool-star atmospheres including departures from LTE. We use near-infrared spectra collected with the CRIRES instrument at the ESO VLT as reference observational data. We find that the effective temperatures obtained by the different studies mostly agree to better than 100 K. We see a much worse agreement in the surface gravities and metallicities. We demonstrate that non-LTE effects are negligible for Fe I in M-dwarf atmospheres but are important for K I. These effects, leading to K abundance and metallicity corrections on the order of 0.2 dex, may be responsible for some of the discrepancies in the published analyses. Differences in the temperature-pressure structures of the atmospheric models may be another factor contributing to the discrepancies, in particular at low metallicities and high effective temperatures. In high-resolution spectroscopic studies of M dwarfs attention should be given to details of the line formation physics as well as input atomic and molecular data. Collecting high-quality, wide wavelength coverage spectra of benchmark M dwarfs is an essential future step.
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