Abstract

A significant fraction of isolated white dwarfs host strong magnetic fields that range from a few to a thousand Megagauss. These high-field magnetic white dwarfs (HFMWDs) comprise ∼10% of all isolated white dwarfs. Remarkably, not a single close and detached binary system that is composed of a white dwarf and a low-mass-main-sequence star contains a HFMWD. If the origin of magnetic fields in white dwarfs were independent of binary interactions, then the observed distribution of isolated white dwarfs should be similar to those in detached binaries, yet they are not. Unless there is a mechanism by which distant companions prevent the formation of a strong magnetic field, a more plausible explanation is that highly magnetized white dwarfs became that way by engulfing (and removing) their companions. When a member of a binary system extends past its Roche-Lobe, mass transfer and tidal torques serve to distribute material in a circumbinary ‘envelope’ enclosing the system. This process causes the orbit to decay as the ambient material dynamically drags on the binary components. This interaction is referred to as common envelope evolution and is thought to be the primary channel for producing short-period binaries in the Universe. Using three-dimensional numerical simulations, we investigate common envelope events between an Asymptotic Giant Branch (AGB) star and low-mass companions that are expected to result in mergers. As a companion approaches the AGB core, it tidally disrupts. The disrupted material forms an accretion disk which may amplify, transport and anchor the magnetic field onto the proto-white dwarf. At the end of the AGB phase, a HFMWD would emerge.

Library of Congress Subject Headings

White dwarf stars; Cosmic magnetic fields; Accretion (Astrophysics); Asymptotic giant branch stars

Publication Date

4-2022

Document Type

Dissertation

Student Type

Graduate

Degree Name

Astrophysical Sciences and Technology (Ph.D.)

Department, Program, or Center

School of Physics and Astronomy (COS)

Advisor

George M. Thurston

Advisor/Committee Member

Noam Soker

Advisor/Committee Member

Joshua Faber

Campus

RIT – Main Campus

Plan Codes

ASTP-PHD

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