Oxygen opacity of stellar interiors in the laboratory

The so-called “solar problem” was revealed when a change in measured solar abundances produced disagreement between solar model predictions and helioseismic measurements. The discrepancy could be resolved if the opacity of materials at conditions near the convection zone base (CZB) were higher than predicted by models. Oxygen and iron are among the most important contributors to opacity near the CZB. Previous experiments with iron showed notable differences between theory and experiment. To further investigate this topic, we have begun using the previously developed platforms at Z and NIF to study oxygen opacity at the relevant conditions. Coincidentally, the conditions near the solar CZB are similar to some white dwarf stars that contain significant amounts of oxygen. Measurements of oxygen opacity have been carried out using SiO₂ and/or MgO samples at each facility. We will discuss some of the preliminary results from each.

This work was supported in part by the Wootton Center for Astrophysical Plasma Properties under U.S. DOE cooperative agreement number DE-NA0003843, the Z Facility’s Fundamental Science Program, and NIF’s Discovery Science Program.