Measuring Metallicities of M Dwarf Stars
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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.