Date of Award

7-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace, Physics, and Space Sciences

First Advisor

Samuel Durrance

Second Advisor

Terry Oswalt

Third Advisor

Ming Zhang

Fourth Advisor

Mary Sohn

Abstract

So far, the most promising theory for the existence of subdwarf B (sdB) stars is that they were formed during binary star evolution. This research was conducted to test this theory by searching for companions around six sdB pulsators (V391 Peg, HS 0702+6043, EC 20117-4014, PG 1219+534, PG 0911+456, and PG 1613+426) using the Observed-minus-Calculated (O-C) method. A star’s position in space will wobble due to the gravitational forces of any companion. If the star is emitting a periodic signal, the orbital motion of the star around the system’s center of mass causes periodic changes in the light pulse arrival times. After obtaining the O-C diagrams for these stars, useful limits on suspected companions’ minimum masses and semimajor axes were calculated. In addition, “period vs. amplitude” and “mass vs. semimajor axis” modeling were conducted to investigate the ranges and combinations of possible companion masses and semimajor axes that are consistent with the observational data. For V391 Peg and HS0702+6043, companions noted in previous publications validated the method used in this research and confirmed their existence. The results of this study of both these targets yield the same masses and semimajor axes as the published ones, within the uncertainties. For EC20117-4014, current data show that there is a companion and the signal of a companion candidate was detected with higher than 90% of confidence level. However, there is still several possible mass and semimajor axis combinations of the companion star. For PG1219+534, current data suggest that there may be a companion, however, the no-companion possibility still cannot be eliminated. The results of this project discovered two new possible companion candidates to EC20117-4014 and PG1219+534, confirmed companions previously detected in V391 Peg and HS0702+6043, as well as provided preliminary evidence for companions to EC20117- 4014 and PG1219+534 at the will require further observation. Though still a small sample, these results suggest that planets might survive the post-main-sequence evolution of their parent stars.

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