2005ApJ...622.1044S

The fast, dense winds that characterize Wolf-Rayet (W-R) stars obscure their underlying cores and complicate the verification of evolving core and nucleosynthesis models. Core evolution can be probed by measuring abundances of wind-borne nuclear-processed elements, partially overcoming this limitation. Using ground-based mid-infrared spectroscopy and the 12.81 µm [Ne II] emission line measured in four Galactic W-R stars, we estimate neon abundances and compare them to long-standing predictions from evolved-core models. For the WC star WR 121, this abundance is found to be ≳11 times the cosmic value, in good agreement with predictions. For the three less-evolved WN stars, little neon enhancement above cosmic values is measured, as expected. We discuss the impact of clumping in W-R winds on this measurement and the promise of using metal abundance ratios to eliminate sensitivity to wind density and ionization structure.