Stellar modeling with low-temperature on-the-fly opacity
AdvisorFerguson, Jason W.
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Accurate stellar modeling requires using our understanding of phenomena far smaller than humans can observe to study some of the largest objects in the universe. One quantity that bridges this gap is the mean opacity, which uses knowledge about atomic and molecular interactions with light to inform how photons carry energy through a star. As the mean opacity depends on both the quantum mechanics of atoms and molecules and the macroscopic properties of the star (temperature, density, composition) it can be tricky to calculate. Traditionally, stellar modeling programs avoid the time-consuming computation of opacity by interpolating off of pre-made opacity tables. However, this interpolation introduces the possibility of error. In low-temperature areas of a star (less than 10,000K), this error is likely to be largest when the composition of the star differs from the composition used to create the tables. One way to examine this error is to model stars using low-temperature opacity values calculated on-the-fly. In this case, on-the-fly means using opacity calculated as the star is being modeled by a low-temperature opacity code using the exact temperature, density, and composition of each region within the star. This work describes the process of adapting the Atlas Opacity Program (ATOP) for use as an on-the-fly opacity code and discusses the results of using on-the-fly opacity values for several stellar evolution models created with the Modules for Experiments in Stellar Astrophysics (MESA) code. These models show that the effect of using on-the-fly opacity is more pronounced in models where the relative abundance of carbon to oxygen in the outer layers of the star changes significantly over the course of the star’s evolution.
Thesis (M.S.)-- Wichita State University, College of Liberal Arts and Sciences, Dept. of Mathematics, Statistics, and Physics