银河系中的M矮星问题
The M Dwarf Problem in the Galaxy
摘要：
我们提出的证据表明，有一个M矮星的问题类似于以前确定的G矮星和K矮星的问题：低金属丰度的M矮星的数量是不够的，以匹配简单的闭盒模型的本地银河系化学演化。我们估计4141 M矮星的金属丰度与光谱从斯隆数字巡天（SDSS）使用分子带强度与金属丰度校准开发使用高分辨率光谱附近的M矮星。使用一个样本的M矮星测量的星等，弛豫和金属丰度，我们推导出一个关系，描述了绝对星等变化的金属丰度的函数。当我们检查SDSS恒星的金属丰度分布时，在对由星等限制巡天采样的不同体积进行校正后，我们发现存在M矮星问题，在[Fe/H] ~-0.5处的M矮星数量小于[Fe/H] = 0处的数量的1%，其中一个简单的银河系化学演化模型预测随着金属丰度的降低，恒星数量会逐渐减少。
英文摘要：
We present evidence that there is an M dwarf problem similar to the previously identified G dwarf and K dwarf problems: the number of low-metallicity M dwarfs is not sufficient to match simple closed-box models of local Galactic chemical evolution. We estimated the metallicity of 4141 M dwarf stars with spectra from the Sloan Digital Sky Survey (SDSS) using a molecular band strength versus metallicity calibration developed using high resolution spectra of nearby M dwarfs. Using a sample of M dwarfs with measured magnitudes, parallaxes, and metallicities, we derived a relation that describes the absolute magnitude variation as a function of metallicity. When we examined the metallicity distribution of SDSS stars, after correcting for the different volumes sampled by the magnitude-limited survey, we found that there is an M dwarf problem, with the number of M dwarfs at [Fe/H] ~ -0.5 less than 1% the number at [Fe/H] = 0, where a simple model of Galactic chemical evolution predicts a more gradual drop in star numbers with decreasing metallicity.
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