Pulsating White Dwarfs in the Open Star Cluster M67

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics and Astronomy

Date of Award

Summer 2021

Abstract

White dwarfs are some of the most versatile tools in the universe. Their ages can provide a lower limit to the age of the universe, and their masses and structure can inform us about the inner workings of the stars they came from. Asteroseismic studies of pulsating white dwarfs have greatly increased our knowledge about the masses of the atmospheric layers, which are crucial to determine the cooling rate of white dwarfs. Knowing the cooling rate will tell us much about the age of the white dwarf and in turn, the age of the universe. In this study, we present the first time-series photometry of pulsating white dwarf candidates in the open star cluster Messier 67. By looking at an ensemble of white dwarfs in an old, open cluster such as Messier 67, we can begin to constrain which properties of stars affect the thicknesses of the atmospheric layers. Standard stellar evolutionary theory suggests the atmospheric structure of each white dwarf in the sample should be identical, as they came from nearly identical progenitor stars; this prediction has yet to be tested. This sample of spectroscopically confirmed white dwarfs comes from a previous study of the white dwarf population in Messier 67. Six hours of time-series photometry are analyzed for pulsation-driven luminosity changes. We find one definite pulsator that is not a cluster member and evidence of variability in three additional white dwarfs that are cluster members. If these additional white dwarfs can be confirmed to be variable, then they can be subject to the time-intensive follow-up observations necessary to search for differences in their atmospheric structures.

Advisor

Kurtis Williams

Subject Categories

Astrophysics and Astronomy | Physical Sciences and Mathematics

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