Detailed chemical analysis of M dwarf stars
Veyette, Mark Joseph
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M dwarf stars are the most abundant stars in the Galaxy and appear to host the vast majority of temperate, Earth-sized planets. Investigations into their detailed compositions are important for inferring the chemical evolution of the Galaxy and for understanding relationships between stellar composition and planet occurrence. However, detailed characterization of M dwarfs is hampered by a unique set of challenges due to their lower effective temperatures. Previous attempts to measure the compositions of M dwarfs relied on observations of M dwarfs with F-, G-, or K-type companions to calibrate metallicity-sensitive features in their near-infrared spectra. These methods are indirect tracers of metallicity, using sodium and calcium lines to estimate iron abundance and overall metallicity. As such, they are not suited for detailed chemical analysis. Utilizing state-of-the-art stellar atmosphere models, I showed that previous M dwarf metallicity calibrations are more sensitive to carbon and oxygen abundances than they are to overall metallicity. By accounting for the effects of carbon and oxygen, I developed the first calibrated method to directly measure the abundances of individual elements in M dwarfs. I showed that the abundances of iron and titanium can be measured directly from iron and titanium lines in high-resolution Y-band spectra. The relative abundance of titanium to iron correlates with stellar age due to the chemical evolution of the Galaxy. I showed that titanium enhancement combined with kinematics can constrain the ages of individual field M dwarfs. I developed a method to measure chemo-kinematic ages of M dwarfs and used it to investigate the tidal evolution of planets on eccentric, short-period orbits around M dwarfs. I found that short-period planets around M dwarfs can maintain non-zero eccentricities for at least 9 Gyr. Detailed chemical analysis of Sun-like stars is now being carried out by the hundreds of thousands thanks to numerous high-resolution spectroscopic surveys at optical wavelengths. In this dissertation, I reviewed current and planned spectroscopic surveys at near-infrared wavelengths that are amenable to M dwarf abundance analysis and presented a case study design of a compact, high-resolution, near-infrared spectrometer for 5-meter class telescopes.
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