## All Theses

8-2008

Thesis

#### Degree Name

Master of Science (MS)

Physics

King, Jeremy R.

#### Committee Member

Brittain , Sean D.

#### Abstract

We analyze elemental abundances of the common proper motion pair HD 134439 and HD 134440 to understand their formation history. This pair of metal-poor ([Fe/H]$\sim -1.50$) halo dwarfs are known, from previous studies, to exhibit abnormally low [$\alpha$/Fe] ratios compared to typical Galactic halo stars. Some have attributed this to planetesimal accretion; others believe these stars formed in the dusty part of a dwarf spheroidal galaxy and were later captured by our Galaxy. To investigate this anomaly, we measure carbon, nitrogen, and oxygen abundances for HD 134439 and HD 134440 from near-UV molecular features using high-resolution spectra obtained with Keck HIRES spectrograph. The [C, N, O/Fe] ratios range from $\sim -0.30$ to $\sim -0.60$ dex. We confirm a previously suggested correlation between the elemental abundances and condensation temperature at the $\sim$5\% confidence level. A comparison of HD 134439 and HD 134440 with stars of similar metallicity in the Galactic halo suggests very different formation histories; though, the abundances of dwarf spheroidal stars seems less different from our stars. Chemical yields of low mass Type II supernovae provide an explanation for most of the abundance patterns observed for the common proper motion pair. Finally, the peculiar abundances of neutron-capture elements (Y, Ag, Ba, Eu) are put in context with various nucleosynthetic sources.

COinS