Date of Award

7-2018

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Aerospace, Physics, and Space Sciences

First Advisor

Saida Caballero-Nieves

Second Advisor

Véronique Petit

Third Advisor

Jean C Perez

Fourth Advisor

Eric Perlman

Abstract

Recent surveys have found that ∼10% of massive stars host strong, mostly dipolar magnetic fields with strengths on the order of a kilogauss. The prominent idea describing the interaction between the stellar winds and the magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the ionized wind material is forced to move along the closed magnetic field loops and collides at the magnetic equator, creating a shock (Δv ∼ 500−800 km s−1). As the shocked material cools radiatively, it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and probing the wind material confined by the magnetic fields of these stars. Some of these magnetic B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. A comparison between the observed and predicted X-ray luminosities was previously performed and lead to a determination of a group of stars with higher observed X-ray luminosity than predicted. This region was comprised of mostly rapid rotators and one slow rotator with a complex field. To address the issue of this overluminous region, I add new X-ray observations of rapidly rotating B-type stars, implement updated stellar and magnetic parameters, and adjust the theoretical models for a geometrically appropriate shock retreat. These adjustments affect the entire sample of known magnetic B-type stars. Furthermore, I focus on the theoretical model, developed for slow rotators, by implementing a more appropriate efficiency scheme and the physics of rapid rotation. Addressing the one slow rotator in the overluminous group with a complex field geometry, I examine how the assumption of a dipolar magnetic field affects the predicted X-ray luminosity of a complex field geometry. I then use an arbitrary field adaptation to theoretical models to determine the shock and post-shock parameters of complex field loops. The subsequent predicted X-ray luminosity is calculated and compared with those determined by the previous models. The possibility of absorption from the cool, dense gas within the magnetosphere was shown to be minor in this case. Modifying analytical models for rapid rotation and complex field geometries is a vital step in furthering models and providing constraints for evolutionary models.

Comments

Copyright held by author

Download

Share

COinS