Graduation Semester and Year
Spring 2025
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Physics and Applied Physics
Department
Physics
First Advisor
Dr. Nevin N. Weinberg
Second Advisor
Dr. Zdzislaw E. Musielak
Third Advisor
Dr. Sangwook Park
Fourth Advisor
Dr. Amir Shahmoradi
Fifth Advisor
Dr. Manfred Cuntz
Abstract
This thesis compiles the collection of works in nonlinear astroseismology and its implication to the δ Sct variable that we carried over the course of five years. With the advent of high-resolution space missions such as the Kepler and TESS telescopes, we were able to see significant progress in the field in recent years. Nonetheless the new technologies also brought an increasing number of observation that are seemingly contradictory to the linear theory of asteroseismology. In particular, we find the δ Sct variable, which eludes our models in terms of how varied we find they spectra for stars with very similar global parameters (be it mass, ages, surface temperatures and gravity, see Balona & Dziembowski 2011; Bowman & Kurtz 2018), with little to no correlation between the frequencies and the position of δ Scuti stars in the Hertzsprung-Russell diagram (see Balona 2021). Furthermore, ensemble studies of these stars reveal that their amplitude and phase variations happen on timescale that are much shorter than the expectations from stellar variations (Bowman et al. 2016; Breger & Pamyatnykh 1998), leading to many different proposed mechanisms to explain these various observations. Among them, and the most relevant for us, is the use of nonlinearities to explain amplitude and phase variations in their spectra. The most convincing evidence being the treatment of a single δ Scuti KIC 8054146, by Breger and Montgomery 2014, which demonstrates some of the most significant signals in their spectra can be correctly modelled through the nonlinear direct mode coupling mechanism. This result ignited the works we performed and relay in this thesis, where this coupling mechanism will be central. In it we demonstrate the implications of nonlinear wave interactions for these stars, solidify and compile the theoretical constructions to the evidence of direct nonlinear coupling in δ Sct, and establish the prevalence of nonlinearly directly coupled waves in δ Sct models with a wide range of global stellar parameters (MW23). We then show that we can limit the growth of unstable linearly driven waves with a novel proposed system of equations that utilize two nonlinear wave-wave mechanisms to model these interactions in physical stars while still preserving the observable relationship of interest from direct coupling (MW25).
Keywords
Asteroseismology, Nonlinear wave dynamics, Mohammed Mourabit, Astronomy, Astrophysics, Physics, Delta Scuti, Variable stars, Stellar physics
Disciplines
Astrophysics and Astronomy | Fluid Dynamics | Stars, Interstellar Medium and the Galaxy | Statistical, Nonlinear, and Soft Matter Physics
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Mourabit, Mohammed, "Nonlinear Wave Dynamics in Asteroseismology with Application to delta Scuti Stars" (2025). Physics Dissertations. 179.
https://mavmatrix.uta.edu/physics_dissertations/179
Included in
Fluid Dynamics Commons, Stars, Interstellar Medium and the Galaxy Commons, Statistical, Nonlinear, and Soft Matter Physics Commons
Comments
The works offered in this Dissertation was realized under the supervision and support of my advisor Dr. Nevin N. Weinberg and supported through the NASA ATP grant 80NSSC21K0493.