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_e~ 180 eV, n_e ~ 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 measured oxygen opacity in multiple Z experiments using SiO₂ samples. The Si K-shell spectrum is less perturbed by density effects and provides plasma diagnostic information. Preliminary inferred plasma conditions were T_e = 160 eV and n_e = 8x10²¹ cm^-3. The 5-19 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. Experimental results, reproducibility, and initial comparisons with opacity model 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.