White dwarf coalescences

  • A good fraction of white dwarfs are found in binary systems and, in many cases, they will exchange mass during their lifetime. The mass transfer phase will change the course of their live to stages that single stars cannot attain. During this phase a white dwarf system can either merge or survive as a binary in a semi-detached configuration, the so-called AM CVn system. White dwarf mergers are believed to result in extreme Helium stars, R Corona Borealis stars, neutron stars and, maybe most spectacularly, type Ia supernovae. While for many years type Ia supernova were thought to result from a white dwarf star acquiring mass from a normal star, the lack of hydrogen in the spectra, the recent discoveries of supra-Chandrasekhar mass supernovae, the delay time distribution measurements, all favor the white dwarf merger model. This underlines the necessity to clarify the fate of mass-transferring double white dwarfs. In this thesis we present the results of a systematic study scanning‚ the white dwarf binary parameter space. In a first step we investigate the onset and the subsequent dynamics of mass transfer. We find that the mass transfer is long-lived, continuing for several dozen orbital periods. The second step of this study examines the parameter space region where detonations may occur during the mass transfer phase, or at surface contact when the donor is tidally disrupted and plunges into the accretor. We demonstrate that a wide variety of dynamically unstable systems are viable type Ia candidates. A large fraction of Helium-accreting binary systems explode at surface contact and/or at earlier times via detonations induced by instabilities in the accretion stream. We do not find definitive evidence for an explosion in any of the studied double Carbon-Oxygen systems. The next decade thus holds enormous promise for the study of these events, in particular with the advent of wide-field synoptic surveys allowing a detailed characterization of their explosive properties.

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Meta data
Publishing Institution:IRC-Library, Information Resource Center der Jacobs University Bremen
Granting Institution:Jacobs Univ.
Author:Marius Dan
Referee:Stephan Rosswog, Marcus Brüggen, Gijs Nelemans
Advisor:Stephan Rosswog
Persistent Identifier (URN):urn:nbn:de:101:1-201305294876
Document Type:PhD Thesis
Date of Successful Oral Defense:2012/03/27
Year of Completion:2012
Date of First Publication:2012/11/29
PhD Degree:Physics
School:SES School of Engineering and Science
Library of Congress Classification:Q Science / QB Astronomy / QB460-466 Astrophysics
Call No:Thesis 2012/42

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