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Stellar modeling with low-temperature on-the-fly opacity
Buchele, Lynn
Buchele, Lynn
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2021-05
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Abstract
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.
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Thesis (M.S.)-- Wichita State University, College of Liberal Arts and Sciences, Dept. of Mathematics, Statistics, and Physics
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Wichita State University
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© Copyright 2021 by Lynn Buchele
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