Calculating the Ephemeris of a Rotating White Dwarf Star

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics and Astronomy

Date of Award

Spring 5-1-2026

Abstract

Approximately half of the studied ultra-massive, highly magnetic white dwarfs (WDs) display photometric variability ranging from 60 seconds to several hours. By ex- cluding alternative hypotheses, it is generally assumed that this variability originates from a spot on the surface of a rapidly rotating WD. Under this assumption, changes in the rotational period are expected over long timescales as an effect of the pulsar mechanism or internal differential rotation. On shorter time scales, detectable period variations may indicate longitudinal migration of the spot, changes in spot geometry, or evidence that the variability stems from ellipsoidal variations rather than rotation. The primary goal of this research is to calculate an ephemeris for a rotating WD and determine the accu- racy and precision with which pulse timing can be achieved using meter-class, ground- based telescopes. Results are presented for the initial monitoring of WDJ 0006+3104, an ultra-massive magnetic WD exhibiting a photometric variability of 23.1538 minutes with a standard deviation of 23 seconds. These findings suggest that approximately 400 years of monitoring would be required to detect a noticeable period shift due to the pulsar mecha- nism and gravitational wave radiation. Consequently, any period change observed through long-term monitoring must be due to an alternative physical source. Overall, these early findings indicate that the method for calculating the ephemeris has suitable accuracy and precision. Consistent observations of the WD over the next decade are expected to provide a comprehensive understanding of its rotational evolution.

Advisor

Kurtis Williams

Subject Categories

Astrophysics and Astronomy | Physical Sciences and Mathematics

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