Overview

When did the Galaxy's stars form? I address this question by investigating the enrichment history of the r-process elements, which form in core-collapse supernovae. I begin by establishing a method by which I measure the abundance of europium, which is almost entirely generated in the r-process, in solar neighborhood stars. The least-squares fitting technique matches LTE synthetic spectra with observed spectra. I demonstrate the technique's accuracy by comparing my results with literature values for 41 stars. I then apply my technique to a full complement of 1070 stars in the solar neighborhood, the largest catalog of europium abundances compiled to date. Comparing my europium results with other properties of those stars, I investigate europium's correlation with a number of qualities, most notably stellar age. I conclude that europium abundance versus time is constant, rising only 0.06 dex over the past 10 Gyr, with an RMS scatter of ∼0.2 dex during that time. Europium abundance and iron abundance are strongly correlated: star forming regions that were significantly enriched by iron-producing supernovae were also significantly enriched by r-process-producing supernovae. Further, the two types of supernovae do not detonate in a constant proportion over the Galaxy's history. In comparing europium abundance with extrasolar planet occurrence, systems with planets have more europium, given their iron abundance, than systems without planets. While europium itself is not abundant enough to influence planet formation directly, it is possible that other elements produced in the same supernovae, e.g., oxygen, do play some role in planet formation. One limitation of field stars in determining the Galaxy's enrichment history is the uncertainty in their ages. To address this issue, I also measure europium abundances in 64 stars within nine open clusters. The result that europium levels have been constant over the past 8-10 Gyr persists. I also announce the existence of two Jovian-mass extrasolar planets orbiting intermediate mass stars in eccentric orbits. Intermediate mass stars are difficult targets for radial velocity planet searches, so these new planets fill out our understanding of the mass distribution of exoplanet hosts.

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9781243769336

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