M dwarf metallicities and exoplanets

This dissertation is primarily focused on the topic of M dwarf metallicities and their relevance to the study of extrasolar planets. I begin by describing a method for accurately determining M dwarf metallicities with spectral synthesis based on abundance analyses of visual binary stars. I then apply this technique and present the first spectroscopic metallicities of three M dwarfs with planetary mass companions. The three M dwarf planet hosts have sub-solar metallicities, a surprising departure from the trend observed in FGK-type planet hosting stars. I discuss the implications of this result for extrasolar planet searches around the most numerous stars in the galaxy. I also present measured metallicities for a select group of M dwarfs with precisely determined masses and luminosities. Comparison of these stars' V band magnitudes with the predictions of the current state-of-the-art theoretical models for low-mass stars indicate that the models are deficient, as previously thought. I discuss how the cool star model atmospheres that were developed for the metallicity analysis technique might be used to improve M dwarf structure and evolution models. In addition to M dwarf metallicities, I describe some complementary work to determine the true mass of an extrasolar planet candidate using a combined analysis of high-precision astrometry and radial velocities. I present a dynamical mass for the companion to HD 33636 that indicates it is a low-mass star instead of an exoplanet. This result demonstrates the value of follow-up astrometric observations to determine the true masses of exoplanet candidates detected with the radial velocity method. Finally, I discuss the broader implications of the results presented in this dissertation and the prospect for similar work in the future.