A Physically Motivated and Empirically Calibrated Method to Measure the Effective Temperature, Metallicity, and Ti Abundance of M Dwarfs
A Physically Motivated and Empirically Calibrated Method to Measure the Effective Temperature, Metallicity, and Ti Abundance of M Dwarfs
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DOI：
10.3847/1538-4357/aa96aa
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发表时间：
2017-10
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影响因子：
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通讯作者：
M. Veyette;P. Muirhead;A. Mann;J. Brewer;F. Allard;D. Homeier
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作者：
M. Veyette;P. Muirhead;A. Mann;J. Brewer;F. Allard;D. Homeier
对类太阳的F、G和K型恒星进行详细的化学分析的能力是一个强大的工具，具有许多应用，包括研究银河系的化学演化和约束行星形成理论。不幸的是，对较冷的恒星大气建模的复杂性阻碍了对M矮星的类似分析。从中等分辨率光谱测量M矮星金属丰度的经验校准方法目前仅限于测量总体金属丰度，并依赖于恒星群体中的天体物理丰度关联。我们提出了一种新的合成M矮星谱的经验定标，它可以用来推断有效温度、Fe丰度和Ti丰度。我们在Keck II上用NIRSpec获得了29M矮星的高分辨率(R∼25,000)Y带(∼1μm)光谱。使用菲尼克斯恒星大气模拟程序(版本15.5)，我们生成了涵盖一系列温度、金属度和阿尔法增强的合成光谱网格。根据我们的观测和合成光谱，我们测量了多条Fei和Tii谱线的等效宽度和基于FeH带头的温度敏感指数。我们使用从遥远的太阳类型伴星测量的丰度，对观测到的指数和等效宽度的转换进行了经验校准，迫使其与模型相一致。我们的校准精度分别为60K、0.1Dex和0.05Dex，并校准为3200K<；Tef<；4100K、−0.7<；[Fe/H]<；+0.3和−0.05<；[Ti/Fe]<；+0.3。这项工作是对M矮星进行详细化学分析的一步，其精度与对FGK恒星的分析结果类似。
The ability to perform detailed chemical analysis of Sun-like F-, G-, and K-type stars is a powerful tool with many applications, including studying the chemical evolution of the Galaxy and constraining planet formation theories. Unfortunately, complications in modeling cooler stellar atmospheres hinders similar analyses of M dwarf stars. Empirically calibrated methods to measure M dwarf metallicity from moderate-resolution spectra are currently limited to measuring overall metallicity and rely on astrophysical abundance correlations in stellar populations. We present a new, empirical calibration of synthetic M dwarf spectra that can be used to infer effective temperature, Fe abundance, and Ti abundance. We obtained high-resolution (R ∼ 25,000), Y-band (∼1 μm) spectra of 29 M dwarfs with NIRSPEC on Keck II. Using the PHOENIX stellar atmosphere modeling code (version 15.5), we generated a grid of synthetic spectra covering a range of temperatures, metallicities, and alpha-enhancements. From our observed and synthetic spectra, we measured the equivalent widths of multiple Fe i and Ti i lines and a temperature-sensitive index based on the FeH band head. We used abundances measured from widely separated solar-type companions to empirically calibrate transformations to the observed indices and equivalent widths that force agreement with the models. Our calibration achieves precisions in Teff, [Fe/H], and [Ti/Fe] of 60 K, 0.1 dex, and 0.05 dex, respectively, and is calibrated for 3200 K < Teff < 4100 K, −0.7 < [Fe/H] < +0.3, and −0.05 < [Ti/Fe] < +0.3. This work is a step toward detailed chemical analysis of M dwarfs at a precision similar to what has been achieved for FGK stars.