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White Dwarf Dynamical Interactions

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White Dwarf Dynamical Interactions Front cover: Temperature profile during the first mass transfer episode in a UNIVERSITAT POLITÈCNICA DE CATALUNYA simulation of the core-degenerate scenario. Back cover: The development of a detonation in a direct collision INSTITUT D’ESTUDIS ESPACIALS DE CATALUNYA between a helium-core white dwarf and a carbon-oxygen one. Clockwise from top-left: density, temperature, and titanium and iron abundances. PhD Thesis WHITE DWARF DYNAMICAL INTERACTIONS Gabriela Aznar Siguan White dwarf dynamical interactions Gabriela Aznar Siguan Universitat Politecnica` de Catalunya Departament de F´ısica Aplicada White dwarf dynamical interactions by Gabriela Aznar Siguan A thesis submitted fot the degree of Doctor of Phylosophy Advisors: Enrique Garc´ıa–Berro Montilla Pablo Loren´ Aguilar Castelldefels, Enero de 2015 Curso académico: Acta de calificación de tesis doctoral Nombre y apellidos Programa de doctorado Unidad estructural responsable del programa Resolución del Tribunal Reunido el Tribunal designado a tal efecto, el doctorando / la doctoranda expone el tema de la su tesis doctoral titulada ____________________________________________________________________________________ __________________________________________________________________________________________. Acabada la lectura y después de dar respuesta a las cuestiones formuladas por los miembros titulares del tribunal, éste otorga la calificación: NO APTO APROBADO NOTABLE SOBRESALIENTE (Nombre, apellidos y firma) (Nombre, apellidos y firma) Presidente/a Secretario/a (Nombre, apellidos y firma) (Nombre, apellidos y firma) (Nombre, apellidos y firma) Vocal Vocal Vocal ______________________, _______ de __________________ de _______________ El resultado del escrutinio de los votos emitidos por los miembros titulares del tribunal, efectuado por la Escuela de Doctorado, a instancia de la Comisión de Doctorado de la UPC, otorga la MENCIÓN CUM LAUDE: SÍ NO (Nombre, apellidos y firma) (Nombre, apellidos y firma) Presidente de la Comisión Permanente de la Escuela de Secretario de la Comisión Permanente de la Escuela de Doctorado Doctorado Barcelona a _______ de ____________________ de __________ i Summary Because of their well known observational properties Type Ia, or thermonuclear, supernovae are used as standard candles, and have allowed the discovery of the accelerating expansion of the Universe. Yet, despite their importance, we still do not know exactly which stellar systems produce them. However, we do know the physical mechanism that powers the explosion. Type Ia supernovae originate from the explosion of carbon-oxygen white dwarfs. It has long been suggested that a white dwarf in a binary system — with either another white dwarf, through the so-called double-degenerate channel, or a main-sequence or red giant companion through the single-degenerate channel — could give rise to a Type Ia supernova event. Yet, despite the recent breakthrough detections of relatively nearby SNe Ia, including 2011fe and 2014J, no normal stellar progenitor has ever been directly identified. Overall, the challenging, unsolved stellar progenitor problem for SNe Ia stands in marked contrast to the case of core-collapse supernovae, whose stellar progenitors are highly-luminous, massive stars. Observational evidence favors the double-degenerate channel, but significant discrepancies exist between observations and theory. There are approximately a few hundred million double white dwarf systems in the Milky Way alone and their study would help to establish whether one can produce sufficient type Ia supernovae via this route. Nevertheless, even if a white dwarf merger does not succeed in exploding, other interesting phenomena might result. R Coronae Borealis, magnetars and high-field magnetic white dwarfs, could be the product of white dwarf mergers. In this work we simulate and study several scenarios which involve interacting white dwarfs. One of the classical scenarios is the double-degenerate one, in which the merger of both white dwarfs in the binary system occurs after gravitational radiation has brought the stars close enough to overflow the Roche lobe. In this case a circular orbit with synchronized stars is the expected initial configuration of the interaction. However, other mechanisms that make two white dwarfs interact exist that have not been carefully studied. We first consider the so-called core-degenerate scenario, in which both white dwarfs merge just at the end of the common envelope phase. In this case the merger is driven by the interaction with the circumbinary disk resulting from previous evolution. Within this scenario the transfer of angular momentum from the binary to the disk decreases the separation of the pair whilst the eccentricity of the system increases. This results in an eccentric binary system in which the core ii of the AGB star is hot. Secondly, we study close encounters of two white dwarfs in dense stellar environments, like the cores of old globular clusters or the central regions of galaxies. In some cases these close encounters lead to collisions. We analyze how the different initial conditions change the type of interaction obtained, the outcome of such interactions and the characteristics of the remnants. We also study the observational imprints of these interactions. These include the emission of gravitational waves, the X-ray luminosities, the thermal neutrino emission and the bolometric light curves. Finally, we analyze two possible outcomes of the merger of white dwarfs. Namely, we study if a merger of two white dwarfs can produce high-field magnetic white dwarfs or anomalous X-ray pulsars. iii I have hardly ever known a mathematician who was able to reason. Stephen Hawking Acknowledgments Decid´ı empezar la tesis doctoral despu´es de haber realizado el proyecto final de m´aster bajo la supervisi´on de los doctores Enrique Garc´ıa-Berro Montilla y Pablo Lor´en Aguilar. Tal y como dijo Enrique entonces, la colaboraci´on en investigaci´on es como un noviazgo. En mi caso fue as´ı, una vez conocidos decidimos formalizar y continuar la relaci´on durante cuatro a˜nos m´as. Fruto de esta relaci´on ha sido diversos art´ıculos cient´ıficos y nuevos caminos abiertos para una eventual investigaci´on futura. Aunque yo considero que he aprendido mucho de Pablo y Enrique, Enrique todav´ıa opina que no ha conseguido hacerme superar mis prejuicios matem´aticos. Creo que no he llegado a formar parte de los pocos matem´aticos a los que se refiere Stephen Hawking, sobre todo porque no he tenido el placer de conocerlo, sin embargo tengo la sensaci´on de que gracias a vosotros el razonamiento f´ısico me ha quedado mucho m´as al alcance. Debo agradeceros a los dos la dedicaci´on y el inter´es que me hab´eis prestado. Much´ısimas gracias Enrique y Pablo. Tambi´en me gustar´ıa agradecer a los doctores Santiago Torres y Jorge Rueda por haberme permitido colaborar con ellos. El Dr. Torres puso a mi disposici´on los c´alculos de s´ıntesis de poblaciones que se detallan en el cap´ıtulo dedicado a las enanas blancas con campos magn´eticos elevados. El Dr. Rueda me inici´oen el estudio de los p´ulsares an´omalos de rayos X. Sin la ayuda de ambos esta tesis ser´ıa imcompleta. I would like to thank doctor Stephan Rosswog and its computational high-energy astrophysics group of the Stockholm University the warm welcome they offered me during my stay. I really enjoyed the weekly meetings and interesting talks about astrophysics that I witnessed and held. Thank you very much Stephan, Oleg, Iv´an and Emilio. I hope to see you again. Tambi´en estoy muy agradecida a Illa, una buena amiga que hizo mi estancia m´as agradable. During this time we have collaborated with the nice group from the University of Massachusetts Dartmouth of doctor Robert Fisher. I liked to get to know you in Cefal`u, Rahul and Robert, and hope to keep in touch. I also owe my gratitude to doctor Noam Soker, it was very interesting to listen to you in Cefal`uand to work with you. Aquesta feina desenvolupada durant tants anys s’ha dut a terme rodejada d’una molt bona companyia. A¨ıllats del m´on, a Castelldefels hi ha un despatx de doc- iv torands del departament de f´ısica aplicada molt ben avingut. Especialment valoro haver conegut a unes amigues amb les que he compartit molts bons i mals moments, i en tots ells, elles sempre s’han comportat superant les meves expectatives. Gr`acies Anna, Estel, Ruxandra, Araceli i Maria. Juntament amb el Fran, el Milad, el Char- lie, el Shervin, el Fugqiang i la Isa hem aconseguit estar ben entretinguts. Impartir classes amb els bons professors d’aquesta secci´otamb´eha estat un plaer. I poder haver consultat dubtes als sempre propers astrof´ısics Jordi i Pilar m’ha ajudat molt, gr`acies. Tamb´eles lli¸cons inform`atiques que m’han donat el Toni i el Jordi m’han resultat molt ´utils, gr`acies tamb´e. Ara ´es el torn de referir-me a les amistats m´es properes. Amb aquest parell de l´ınies no puc expressar tota la felicitat i gratitud cap a vosaltres, sin´oque espero que seguim alimentant aquesta relaci´odia a dia durant molt´ıssims anys m´es. Estic molt contenta de poder contar amb la bona amistat dels meus amics de mates. Sense els dinars del mes aquests anys no haurien estat el mateix. Nom´es vosaltres sou capa¸cos d’inventar una tradici´ocom aquesta, ser`aque s´ı que som diferents. Laura, tu sempre em sorprens quan menys m’ho espero. Desitjo que tamb´esigui aix´ıen un any i poguem conviure a Madrid. Les meves grans amigues del cole tamb´emereixen una menci´oespecial, Laura, Anna, Cris i Marta. Aprecio molt la vostra incondicional amistat. Va especialment per tu, Laura. Puc considerar que ets casi de la fam´ılia, Sarah. I agraint-te a tu el teu suport, vull comen¸car el reconeixament cap a la meva estimada fam´ılia.
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