We investigate the use of the gravity sensitive neutral sodium (Na I) doublet at 8183 ? and 8195 ? (Na 8200 ? doublet) as an age indicator for M dwarfs. We measured the Na doublet equivalent width (EW) in giants, old dwarfs, young dwarfs, and candidate members of the β Pic moving group using medium-resolution spectra. Our Na 8200 ? doublet EW analysis shows that the feature is useful as an approximate age indicator in M-type dwarfs with (V – K s ) ≥ 5.0, reliably distinguishing stars older and younger than 100?Myr. A simple derivation of the dependence of the Na EW on temperature and gravity supports the observational results. An analysis of the effects of metallicity shows that this youth indicator is best used on samples with similar metallicity. The age estimation technique presented here becomes useful in a mass regime where traditional youth indicators are increasingly less reliable, is applicable to other alkali lines, and will help identify new low-mass members in other young clusters and associations.
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机译：我们研究了在8183时使用重力敏感的中性钠（Na I）双重峰的情况。和8195吗？ （Na 8200？doublet）作为M矮人的年龄指标。我们使用中等分辨率谱图测量了巨人，旧矮星，年轻矮星和βPic移动组候选成员中的Na双峰等效宽度（EW）。我们的Na 8200吗？ doublet EW分析表明，该特征可用作（V – K s）≥5.0的M型矮星的近似年龄指示符，可以可靠地区分年龄小于100？Myr的恒星。 Na EW对温度和重力的依赖性的简单推导支持了观测结果。对金属性影响的分析表明，该青年指示器最适用于具有相似金属性的样品。本文介绍的年龄估算技术在大众体制下很有用，在这种体制下，传统的青年指标越来越不可靠，适用于其他碱性指标，并且将有助于识别其他青年群体和协会中的新的低质量成员。
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