Line-depth ratios as indicators of effective temperature and surface gravity
Line-depth ratios as indicators of effective temperature and surface gravity
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DOI：
10.1093/mnras/stab1770
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发表时间：
2021-06
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通讯作者：
N. Matsunaga;M. Jian;D. Taniguchi;Scarlet S. Elgueta
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作者：
N. Matsunaga;M. Jian;D. Taniguchi;Scarlet S. Elgueta
恒星光谱的分析依赖于有效温度(Tef)和表面重力(Logg)。然而，对数g的高精度估计是具有挑战性的。一种经典的方法是寻找满足电离平衡的logg，即中性和电离金属线的丰度是一致的。我们提出了一种利用Tef、logg和线深比之间的经验关系的方法，为此，我们仔细地选择了FeI和FeII线对以及CaI和CaII线对。基于42颗FGK星(矮星到超巨星)的YJ波段(0.97-1.32μm)高分辨光谱，我们选取了5个FeI-Fe II和4个CaI-CaII线对和13个FeI-FeI对(用于估算Tef)，并导出了经验关系式。使用这种关系不需要复杂的数字模型和工具来估计化学丰度。我们给出的关系式允许我们分别以大约50K和0.2Dex的精度推导出TJeff和logg，但可达到的精度取决于校准器的恒星参数的精度。必须通过观测具有准确恒星参数的恒星，例如具有星震对数的恒星和考虑到非局部热力学平衡和对流影响的完整恒星模型分析的恒星，来修正定标。此外，我们使用的校准器具有有限的金属丰度范围，−0.2<；[Fe/H]<；+0.2Dex，我们的关系需要在更大范围的金属丰度校准数据集的基础上进行测试和重新校准。
The analysis of stellar spectra depends upon the effective temperature (Teff) and the surface gravity (log g). However, the estimation of log g with high accuracy is challenging. A classical approach is to search for log g that satisfies the ionization balance, i.e., the abundances from neutral and ionized metallic lines being in agreement. We propose a method of using empirical relations between Teff , log g and line-depth ratios, for which we meticulously select pairs of Fe i and Fe ii lines and pairs of Ca i and Ca ii lines. Based on YJ-band (0.97–1.32 μm) high-resolution spectra of 42 FGK stars (dwarfs to supergiants), we selected five Fe i–Fe ii and four Ca i–Ca ii line pairs together with 13 Fe i–Fe i pairs (for estimating Teff), and derived the empirical relations. Using such relations does not require complex numerical models and tools for estimating chemical abundances. The relations we present allows one to derive Teff and log g with a precision of around 50K and 0.2 dex, respectively, but the achievable accuracy depends on the accuracy of the calibrators’ stellar parameters. It is essential to revise the calibration by observing stars with accurate stellar parameters available, e.g., stars with asteroseismic log g and stars analyzed with complete stellar models taking into account the effects of non-local thermodynamic equilibrium and convection. In addition, the calibrators we used have a limited metallicity range, −0.2 < [Fe/H] < +0.2 dex, and our relations need to be tested and re-calibrated based on a calibrating dataset for a wider range of metallicity.