Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Physics and Astronomy


This thesis is divided into three separate sections, each dealing with a problem from the study of stellar variability;In the first section, hot spots on accreting white dwarfs with magnetic fields are investigated. It is found that various loss mechanisms do not destroy the accretion spots and that pulsed ultraviolet radiation will be emitted as the dwarf rotates. This pulsed radiation should be observable from dwarf companions near giant stars undergoing mass loss by a stellar wind and from slowly moving dwarfs accreting from the interstellar medium. White dwarfs in the Hyades cluster may provide some examples of this second case, and it is suggested that these dwarfs be examined for optical color variations;The second section reports on a search for variability in three Hyades white dwarfs, G8-7, G7-41, and G7-255, using observations conducted at Erwin W. Fick Observatory and Kitt Peak National Observatory. Data analysis by the maximum entropy method shows all three stars to be nonvariable in the period range 30s to 1200s. Upper limits on variability are placed at 0.006 to 0.02 magnitudes. No evidence was found for higher amplitude variability at longer periods;In the final section, the use of the O-C diagram as a diagnostic tool in doubly-periodic stars is investigated. A test is developed to distinguish between short and long secondary periods by using the amplitude of the O-C diagram. Application of this test to the RRs variable VZ Cnc establishes that this star is a multiple mode variable, and these results are confirmed by phase dispersion minimization analysis. The O-C amplitude analysis is then applied to the Mira variable R Horologii, with results suggesting that its secondary period is 357('d), rather than the 2856('d) beat period as was previously supposed. A related test of the consistency of the multiple-mode interpretation is also described and used to show that this interpretation is not applicable to the star SZ Lyncis and five Mira variables. These O-C tests have the advantage of being distinctive and easily applied.



Digital Repository @ Iowa State University,

Copyright Owner

Daniel William Peterson



Proquest ID


File Format


File Size

143 pages