Measuring Metallicities of M Dwarf Stars

被称为“M矮星”的恒星是银河系中数量最多的恒星，但它们可能是最不为人所知的。它们构成了附近恒星的70%以上，很可能是太阳系外行星的候选者。它们还可以作为银河系历史的探测器。对M矮星的研究是困难的：即使是附近的矮星也显得非常微弱，它们的光谱是由无数原子和分子吸收线混合在一起的复杂的。PI和她的学生将进行一项观测研究，以开发和校准一种更有效的方法来测量大量M矮星的元素组成。该项目将构成一篇博士论文，本科生将协助观察和数据分析。他们的主要目标是仅使用低分辨率光学光谱测量来测量任何一颗M矮星的金属丰度。这项技术使用了常见的双星自行对，其中较亮的(主要)恒星是F、G或K矮星，而较弱的(次级)恒星是M矮星。主星的金属丰度是使用标准的高分辨率光谱技术直接测量的，而次星的低分辨率光谱则根据其光谱中的广泛分子吸收特征产生一组谱线指数。基本的假设是双星是由相同的原始物质形成的，因此具有相同的金属丰度。从主星和副星的光谱测量中获得的信息被组合在一起，形成了M矮星金属丰度的经验关系。由此得到的经验关系式将允许仅使用M矮星的低分辨率光学光谱观测来估计任何M矮星的金属丰度。

Stars known as "M dwarfs" are the most numerous stars in the Galaxy, yet they are perhaps the least well understood. They constitute over 70% of the nearby stars and are likely candidates for extrasolar planets. They can also serve as probes of the history of the Milky Way galaxy. The study of M dwarfs is difficult: even the nearby ones appear very faint, and their spectra are a complex myriad of atomic and molecular absorption lines all blended together. The PI and her students will carry out an observational study to develop and calibrate a much more efficient way to measure the elemental composition of a large number of M dwarf stars. The project will constitute a PhD thesis, and undergraduate students will assist with the observations and the data analysis. Their primary goal is to measure the metallicity of any single M dwarf using only low resolution optical spectroscopic measurements. The technique uses common proper motion pairs of binary stars in which the brighter (primary) star in the pair is an F, G, or K dwarf, while the fainter (secondary) member is an M dwarf. The metallicity of the primary stars are measured directly using standard high-resolution spectroscopic techniques, while low resolution spectroscopy of the secondaries yield a set of spectroscopic line indices based on broad molecular absorption features in their spectra. The basic assumption is that the binaries were formed from the same natal material and thus have the same metallicity. The information derived from spectroscopic measurements of the primary and secondary star are combined to form an empirical relation of the M dwarf metallicities. The resulting empirical relation will allow the metallicity of any M dwarf to be estimated using only low resolution optical spectroscopic observations of the M dwarf.