Oxygen opacity experiments for stellar interiors.

Testing oxygen opacity calculations is important for understanding the Sun and white dwarf stars. Near the solar convection zone base, T$_{\mathrm{e}}$\textasciitilde 180 eV, n$_{\mathrm{e}}$ \textasciitilde 9e22 electrons/cc, and oxygen is mostly H-like or fully-stripped. Highly-ionized oxygen produces a relatively simple opacity spectrum, but its calculation relies on untested approximations for continuum lowering and line broadening. We initiated stellar oxygen opacity measurements on Z with progress in two key areas: i) target fabrication and ii) extending the measurement spectral range. We created SiO$_{\mathrm{2}}$ half-moon samples with oxygen areal density greater than 1e19 atoms/cm\textasciicircum 2 and successfully recorded transmission through the heated sample on Z. The 6-18.5 Angstrom spectral range includes the critical oxygen bound-free absorption, the Ly beta transition, and the opacity window region on the short wavelength side of the Ly alpha line. The Si K-shell spectrum is less perturbed by density effects and provides plasma diagnostic information. Experimental results and prospects for refining stellar interior calculations will be discussed. Sandia National Laboratories is a multimission laboratory managed and operated by NTESS LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. DOE's NNSA under contract DE- NA0003525.