Program: GS-2017B-Q-47

The light elements have been used to study differences in Galactic structure and the chemical evolution of the Galaxy. The odd light elements in particular are thought to be produced via secondary processes but their abundances are poorly known relative to even elements such as O, Mg, Si, and Ca. Phosphorus for example is thought to be produced by neutron capture on Si isotopes in massive stars and produced during hydrostatic carbon and neon burning. Until recently, there were few stellar abundance measurements of phosphorus, no phosphorus features are found in the optical region of the solar photosphere. We have previously measured P abundances using the infrared P I lines for dwarfs and giants at metallicities of -0.5 < ]Fe/H] < 0.2 using spectra obtained with the Phoenix high resolution infrared spectrometer. These results agree with the results of other IR and UV phosphorus studies and find chemical evolution models of P in the solar neighborhood underproduce P compared to the observations. Yields must be increased by 2.75 for models to match the observed abundances. We propose to measure phosphorus in thin and thick disk FGK stars with metallicities of -1.0 < ]Fe/H] < -0.5 and the Hyades open cluster. The thin and thick disk sample will help constrain the nucleosynthesis processes necessary to model the behavior of phosphorus, specifically the [P/Fe] versus [Fe/H] slope at the low metallicity end. The Hyades sample will provide the first measurements of phosphorus using the IR lines in an open cluster, find if P abundances from the near-IR lines are sensitive in temperature or log g, and will determine the star to star scatter in P abundances in an open cluster.