Na 8200埃双星作为低质量恒星的年龄指示
The Na 8200 Angstrom Doublet as an Age Indicator in Low-Mass Stars
摘要：
我们研究使用重力敏感的中性钠（NaI）在8183埃-8195埃的双重态（Na 8200埃双重态）作为M矮星的年龄指标。我们用中等分辨率的光谱测量了巨星、老矮星、年轻矮星和Beta Pic移动群候选成员的Na双重态等效宽度（EW）。我们的Na 8200埃双合线EW分析表明，该特征可作为（V-K_s）>= 5.0的M型矮星的近似年龄指标，可靠地区分年龄小于1亿年的恒星。Na EW对温度和重力的依赖性的一个简单的推导支持观测结果。对金属含量影响的分析表明，这一年轻指标最好用于金属含量相似的样品。这里提出的年龄估计技术变得有用的质量制度，传统的青年指标越来越不可靠，适用于其他碱线，并将有助于确定新的低质量成员在其他年轻的集群和协会。
英文摘要：
We investigate the use of the gravity sensitive neutral sodium (NaI) doublet at 8183 Angstroms 8195 Angstroms (Na 8200 Angstrom 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 Beta Pic moving group using medium resolution spectra. Our Na 8200 Angstrom 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 show 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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