Time Series and Spectral Analysis in Asteroseismology

Abstract

A major breakthrough in stellar astrophysics occurred a decade ago when a number of space photometry telescopes were launched and began operations. In particular, the NASA space telescope Kepler was constructed with the goal of finding Earth-like planets around other stars in our galaxy. The technique involved observing the same field of stars, searching for dips in the stellar light curves caused by transits of exoplanets. For four years, the Kepler mission observed almost 200,000 stars with a wide variety of spectral types and evolutionary states. The light curves are also ideal for asteroseismology, the study of stellar oscillations. Fitting the frequencies of these oscillations to stellar models returns accurate fundamental properties including mass, luminosity, radius, and age of the observed star. The goal of this thesis is to use a range of asteroseismic data analysis techniques to improve the understanding of the physical properties of various classes of oscillating stars. This thesis is split into four main chapters. Firstly, I follow the adiabatic frequency pattern of the most evolved solar-like oscillators and observe a departure to the well known asymptotic relation. Secondly, I compare Kepler data and stellar models of main-sequence solar-like oscillators to characterise the frequency discrepancy, known as the surface correction. Thirdly, I devise a technique to use the centroid of blended radial-quadrupole modes to accurately determine fundamental stellar parameters in F-type stars. Finally, I investigate a method to detect stellar companions by measuring the modulation of light arrival time using stable oscillation modes, and attempt to apply it to stars of different spectral types.