Finalized PhD theses

Number of entries: 82

Gamma Ray Emission from Type Ia Supernovae

Status: defended (03/07/2009)
Student: Alina Hirschmann
Supervised by: Jordi Isern Vilaboy; Bravo, E.
University: Universitat Politècnica de Catalunya

Eventhough the research on Type Ia supernovae (SNeIa) has increased considerably with the help of new observatories and data, the mechanism that triggers these explosions is still an enigma. Gamma-rays and positrons are the product of the decay of radioactive elements generated in the explosion and…
Status: defended (03/07/2009)
Student: Alina Hirschmann
Supervised by: Jordi Isern Vilaboy; Bravo, E.
University: Universitat Politècnica de Catalunya

Eventhough the research on Type Ia supernovae (SNeIa) has increased considerably with the help of new observatories and data, the mechanism that triggers these explosions is still an enigma. Gamma-rays and positrons are the product of the decay of radioactive elements generated in the explosion and therefore, play a crucial role in understanding the origin of Type Ia SN. They provide information on the internal structure of the ejecta and the effects of the burning front on it and are also the main energy source that powers the lightcurve. In addition, they can give information on the turbulence of the system, explosion asymmetries, Doppler broadening of emission lines, etc. In order to determine the appropriate mechanism of explosion which reproduces at best the observations, several theoretical models have been built taking into account that these events could lodge subsonic (deflagration), supersonic (detonation) or both (delayed detonation) flame regimes. This work focuses on understanding the transport of gamma-ray photons and positrons in the ejecta and how they can provide information on its internal structure. To study this, we have built a Monte Carlo transport code and computed gamma-ray emission simulations in 1D and 3D, using as input the set of mentioned explosion models. The Monte Carlo technique can help solve the problem of radiative transfer by studying the behavior of a representative number of photons and positrons created in SNeIa explosions. The basics of the Monte Carlo method concerns the use of random numbers with appropriate distributions to describe physical aspects. Simulations in 1D are used basically to discern between explosion models while 3D simulations provide information concerning asymmetries in the explosion, rotation and convective mixing features, and possible interaction of the ejecta with the secondary star of the system. As for the transport of gamma-ray photons, gamma-ray spectral and lightcurve simulations have shown to provide information on he ejecta through the analysis of the line shapes and widths. However, these tools alone are not determinant in the discernment of the explosion mechanism. Diagnostic tools such as the study of the different line ratios, determination of supernova age, determination of 56Ni mass, energy of the explosion, fwhm, energy deposition in the ejecta and photoelectric cut-off energy have been used as complementary tools to help constrain the model through future explosion observations. In 3D, we have analyzed the flux as a function of the direction of observation, assuming that we are capable of viewing the system from different lines of sight. The spectra and lightcurves have shown that differences in the flux as a function of the line of sight can reach 10% at the most, which means that the explosion is not very asymmetric. In addition, we have included the binary companion (a main sequence star) in an input model and have carried out simulations for such scenario to see the effects on the gamma-ray emission. The results have shown that the flux is not very sensitive to the change in the line of sight even with the presence of the main sequence companion. A future study will focus on the type of effects the emission might show considering different binary companions. Complementary to the gamma-ray emission, we have also studied the positron transport in the ejecta since these particles play an important role in powering the lightcurve at late times and they can also be closely linked to the positron-electron annihilation 511 keV line seen by INTEGRAL in the Galactic bulge and disk. The study of the positron escape fraction has allowed us to determine a needed supernova rate in the Galaxy to explain the emission INTEGRAL has measured. The rate obtained from our simulations suggests that Type Ia supernovae could be the strongest candidates since they produce the necessary positrons to explain such emission.

Gravitational wave radiation from single and binary white dwarfs

Status: defended (30/04/2009)
Student: Lorén-Aguilar, P.
Supervised by: Jordi Isern Vilaboy; GarcÍa-Berro, E.
University: Universitat Politècnica de Catalunya

En los próximos años la entrada en funcionamiento de los primeros detectores de ondas gravitatorias será una realidad, abriendo de esta manera una nueva ventana observacional de la Astronomía. Es por ello por lo que resulta de especial interés tener a disposición de la comunidad científica modelos…
Status: defended (30/04/2009)
Student: Lorén-Aguilar, P.
Supervised by: Jordi Isern Vilaboy; GarcÍa-Berro, E.
University: Universitat Politècnica de Catalunya

En los próximos años la entrada en funcionamiento de los primeros detectores de ondas gravitatorias será una realidad, abriendo de esta manera una nueva ventana observacional de la Astronomía. Es por ello por lo que resulta de especial interés tener a disposición de la comunidad científica modelos detallados de emisión de ondas gravitatorias que pudieran ser observados por estos detectores y, en particular, por el observatario espacial de ondas gravitatoras LISA, cuyo lanzamiento está previsto en 2014. Por otro lado las enanas blancas son objetos compactos y si están en sistemas binarios o si se encuentran en la zona inestable a pulsaciones podrían emitir ondas gravitatorias con la suficiente intensidad como para ser detectadas. Es por ello que en la presente tesis se ha estudiado la emisión de ondas gravitatorias de enanas blancas pulsantes y de enanas blancas en sistemas binarios. En el primer caso se ha estudiado la emisión de ondas gravitatorias procedentes de tres tipos de pulsaciones no radiales de las enanas blancas: los modos g, r y p. Se ha comprobado que para las pulsaciones de modos g, en las que la fuerza recuperadora es la gravedad, la emisión de ondas gravitatorias es demasiado débil como para ser observada mediante el satélite LISA. Por el contrario, en el caso de las pulsaciones p, donde la fuerza recuperadora es la presión, se ha podido comprobar que la emisión de radiación gravitatoria resultaría tan intensa que daría lugar a una casi inmediata amortiguación de las pulsaciones. En el segundo caso, se ha calculado la emisión de ondas gravitatorias procedente de la coalescencia de sistemas binarios. Usando un código SPH se ha simulado la coalescencia de una gran variedad de sistemas binarios, cubriendo rangos de masas y composiciones iniciales ampliamente representativos de los diferentes tipos de sistemas binarios galácticos. Con ello se ha podido calcular con detalle la forma de la emisión gravitatoria durante la fase de colisión, así como otras características de interés astrofísico de la coalescencia de enanas blancas. En particular, se ha podido demostrar que los sistemas binarios galácticos serán una fuente garantizada para el futuro detector LISA, no solo como generadores de un ruido de fondo contínuo sino como eventos aislados. Adicionalmente se han buscado las características observacionales de este tipo de sucesos, a fin de guiar las observaciones con los detectores de ondas gravitatorias mediante el uso de la emisión electromagnética de alta energía. También se ha analizado la viabilidad del escenario doblemente degenerado (DD) como progenitor de supernovas de tipo Ia, otro de los aspectos por los que la coalescencia de sistemas binarios de enanas blancas es de interés. En particular, se ha podido demostrar que la distrbución final de densidades y temperaturas de los objetos resultantes de las colisiones, en los casos en los que dos estrellas de diferentes masas están involucradas, dificulta mucho la viabilidad del escenario. Es de destacar finalmente que todo ello ha requerido un esfuerzo computacional elevado que sólo ha sido posible mejorando el código SPH que hemos utilizado. En concreto, se ha introducido una nueva y mas moderna prescripción de la viscosidad artificial y se ha paralelizado el código a fin de poder realizar simulaciones de alta resolución en un tiempo asequible.

Variable stars and eclipsing binaries in M31

Status: defended (09/03/2009)
Student: Vilardell, F.
Supervised by: Ignasi Ribas Canudas; Jordi, C.
University: Universitat de Barcelona

The main objective of the PhD thesis is the use of variable stars (Cepheids) and eclipsing binaries for an accurate determination of the distance to M31. The observational data for the project was obtained over the corse of a 4-yr campaign at the 2.5-m INT telescope (La Palma). The survey has provided photometry of some 450 eclipsing binary stars and 410 Cepheid variables. In the case of the eclipsing binaries the photometry is complemented with spectroscopy obtained from the 8-m Gemini North telescope. From the overall analysis, a distance determination to M31 with an uncertainty below 3% is antipated, thus meaning a very significant improvement over the current 10%. The results of this project will help to better establish the Cosmic Distance Scale by accurately calibrating the distance to Local Group galaxies.
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Status: defended (09/03/2009)
Student: Vilardell, F.
Supervised by: Ignasi Ribas Canudas; Jordi, C.
University: Universitat de Barcelona

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Large scale structure and dark energy

Status: defended (30/06/2008)
Student: Anna Cabre Albos
Supervised by: Enrique Gaztañaga
University: Universitat de Barcelona

Physicists currently believe that the universe is composed basically of dark energy (70%) and dark matter (25%), both unknown components. The rest is made of known (barionic) matter. The first part of the thesis studies the clustering in galaxies through the 2 and 3 point auto-correlation function in Sloan Sky Digital Survey (SDSS). This allows a direct measurement of the dark matter component and the global amplitude of fluctuations modulated by some bias. The second part of the thesis cross-correlates CMB (with WMAP data) with fluctuations in the number of galaxies (with SDSS) in order to obtain extra information about the structure of the universe. Dark energy is responsible for the accelerated expansion of the universe during late times. We can detect it through the redshift or blueshift that experiment photons coming from the Cosmic Microwave Background (CMB) when they pass through dark matter potentials (Integrated Sachs-Wolfe effect). A join analysis of both cross and auto correlations represents a novel approach to understand structure formation in the universe.
The standard cosmological model starts with Big Bang, followed by a rapid period of expansion of the universe called inflation. After that, tiny almost homogeneous fluctuations that conform the primordial universe, start to grow while universe expands now in a relatively slow rhythm. 300,000 years…
Status: defended (30/06/2008)
Student: Anna Cabre Albos
Supervised by: Enrique Gaztañaga
University: Universitat de Barcelona

The standard cosmological model starts with Big Bang, followed by a rapid period of expansion of the universe called inflation. After that, tiny almost homogeneous fluctuations that conform the primordial universe, start to grow while universe expands now in a relatively slow rhythm. 300,000 years after the Big Bang, the temperature is low enough to make the universe become neutral after the recombination of atoms with electrons. Photons are almost free of interactions since then and reach us in the form of a Cosmic Microwave Background (CMB). We can measure the spatial anisotropy spectrum of CMB temperatures and compare it to the expected spectrum of acoustic oscillations. This comparison provides a direct geometrical test from which we can deduce that universe is flat or nearly flat. This can be explained if we introduce a new constituent in the universe apart from matter, the dark energy. Dark energy acts as anti-gravity that accelerates the expansion and is also observed through standard candles Supernovae Ia. Although there is a well motivated model that can explain observations, neither dark matter nor dark energy are known elements, so it is important to use the large amount of newly available data to obtain tighter constraints on the constituents of the universe, the evolution of growth perturbations, the expansion history, and also other alternatives, such as modification of gravity at large scales. In the first part of the thesis, we study the Integrated Sachs-Wolfe effect (ISW), through the cross-correlation between large scale clustering, traced by galaxies (in our case from the catalog SDSS) and primordial temperature fluctuations from CMB (using the catalog WMAP). Photons that come from the last scattering surface can be red or blue shifted by the time evolution of fluctuations in the gravitational potentials created by large scale structures, which are traced by the large scale galaxy distribution. The ISW effect gives us information about dark energy (DE), because DE modifies the evolution of dark matter gravitational potential. There is no ISW effect in a flat universe without DE (ie in the Einstein-de-Sitter universe) because in this case the gravitational potential remains constant (in the linear regime, which corresponds to large angular scales). In principle, the ISW effect can probe dark energy independently from other observations, such as Supernovae Ia. The correlation between galaxies in redshift space can also be used to study the evolution of the dark matter gravitational potential in a way that is complementary to the cross-correlation of galaxies with CMB photons. In the second part of the thesis, we will study this effect in the luminous red galaxies of the SDSS. These galaxies trace very large volumes which is important to have more signal, and they have a known evolution which make easy to work with them.

Random matrix models in Chern-Simons theory

Status: defended (02/06/2008)
Student: Tierz, M.
Supervised by: Emilio Elizalde
University: Universitat de Barcelona

Chern-Simmons and zeta functions
Random matrix models in Chern-Simons theory
Status: defended (02/06/2008)
Student: Tierz, M.
Supervised by: Emilio Elizalde
University: Universitat de Barcelona

Random matrix models in Chern-Simons theory

Testing the initial-final mass relationship of white dwarfs

Status: defended (13/03/2008)
Student: Silvia Catalán Ruiz
Supervised by: Jordi Isern Vilaboy; García-Berro, E.
University: Universitat Politècnica de Catalunya

To be added shortly
Status: defended (13/03/2008)
Student: Silvia Catalán Ruiz
Supervised by: Jordi Isern Vilaboy; García-Berro, E.
University: Universitat Politècnica de Catalunya

To be added shortly

Thermal Diagnostics in the LISA Technology Package Experiment

Status: defended (13/12/2007)
Student: Miquel Nofrarias Serra
Supervised by: José Alberto Lobo Gutiérrez
University: Universitat de Barcelona

The LISA Pathfinder mission (LPF) is an ESA mission, with NASA contributions, planned to fly in 2010. The LPF is a technology readiness mission devoted to pave the way to the future spaceborne gravitational wave observatory LISA. The LISA Technology Package (LTP) experiment in the LPF mission will measure…
Status: defended (13/12/2007)
Student: Miquel Nofrarias Serra
Supervised by: José Alberto Lobo Gutiérrez
University: Universitat de Barcelona

The LISA Pathfinder mission (LPF) is an ESA mission, with NASA contributions, planned to fly in 2010. The LPF is a technology readiness mission devoted to pave the way to the future spaceborne gravitational wave observatory LISA. The LISA Technology Package (LTP) experiment in the LPF mission will measure the relative distance between two free falling test masses to the picometer resolution by using both masses as end mirrors of an interferometer together with an active control loop, known as drag-free, that will act to keep the spacecraft centered around the geodetic motion of the masses. The work in this thesis deals with the thermal diagnostics subsystem, intended to measure and characterise the thermal noise contribution to the instrument performance: from the qualification of the high stability electronics designed to measure temperature fluctuations onboard the satellite to the characterisation of heaters aimed to generate controlled perturbation during mission operations. Analytic solutions together with simulations and experimental results have been used to this end. The results obtained have allowed the characterisation of the temperature subsystem and, also, to define a methodology to deal with the thermal data that will be obtained from the satellite during flight operations.

Dark energy problem in Friedmann cosmology with ideal fluid and in modified gravity

Status: defended (30/10/2007)
Student: O.G. Gorbunova
Supervised by: Sergei D Odintsov
University: Tomsk State Pedagogical University

DE problem is investigated
Status: defended (30/10/2007)
Student: O.G. Gorbunova
Supervised by: Sergei D Odintsov
University: Tomsk State Pedagogical University

DE problem is investigated

Cosmology and structure formation

Status: defended (26/06/2007)
Student: Marc Manera Miret
Supervised by: Enrique Gaztañaga

This is an ongoing theses on large scale structure and its relation to dark energy. Both a theoretical and a more data focused aproach is taken. We study the growth of structure in non-standard cosmological models like Dvali Gabadadze and Porrati, Cardassian, or Chapligyn gas. We show the diference in the linear growth of density fluctuations and higer order statistics like the skewness between these models and the LCDM concordance cosmology. Cluster number counts are also considered as a tool discriminating between dark energy models in the future. On a more observational aproach we study the dark energy by analising the crosscorrelation between CMB temperature maps and galaxy surveys, which are dark matter tracers.
In the rst part of this thesis we look at several non-standard cosmological models. These models have been introduced in the literature mainly to explain the accelerated expansion that we see the universe is currently undertaken. We want to study if they can also reproduce the observations of the…
Status: defended (26/06/2007)
Student: Marc Manera Miret
Supervised by: Enrique Gaztañaga

In the rst part of this thesis we look at several non-standard cosmological models. These models have been introduced in the literature mainly to explain the accelerated expansion that we see the universe is currently undertaken. We want to study if they can also reproduce the observations of the large scale structure and its evolution. For doing so we t introduce a formalism to compute the growth of structure in non-standard cosmologies. Then, for each of these non-standard models, we will focus in computing observables like the linear growth, the skewness, or the cluster number counts. In the second part of this thesis we will look at the cross-correlation between CMB-temperature maps and galaxy (or other dark matter tracers ) surveys maps. This cross-correlation is a way to measure the Integrated Sachs Wolfe (ISW) e ect, which can be directly related to the growth of structure. We will use the ISW signal dependence in redshift and in angular scale to constrain and the equation of state parameter w. In this part of the thesis we will also focus on studying di erent error estimators for the sky maps cross-correlation measurements. We will actually present a new method, which estimate the errors in the con guration space. This method will be compared with other error estimators widely used in the literature: the Jack-knife, the Monte Carlo errors and the theoretical harmonic space errors. The problem of bias. In order to compare models to observations we need to address a crucial point: does light trace mass? In other words: how well the structure we see traces the dark matter we can't see?. Are the observations biased tracers of the mass?. This is a key point to be abble to compare models of growth of structure with observations in the real world. Unfortunately in detail, this requires understanding how star's and galaxies form and shine. As the the universe expands, the dark matter clumps into halos and lamentary structure. This can be very clearly seen in dark matter cosmological simulations, which allow us to study the gravitational clustering separately from other (but also interesting) physical e ects. Like galaxies, halos are not perfect traces of the underlying dark matter uctuations, but biased ones. In fact, we believe that galaxies form inside dark matter halos, so that understanding halo bias is the rst step towards understanding galaxy bias. In part three of this thesis we will use a cosmological dark matter simulation to study the halo clustering and bias. More speci cally, we wonder to what extend the the local bias model could be applied to the predictions and analyses of the two and three point halo correlation functions.

Gamma-ray emission from regions of star formation: theory and first observations with the MAGIC telescope

Status: defended (03/03/2006)
Student: Eva Domingo-Santamaria
Supervised by: Cortina, J.; Diego F. Torres
University: Universitat Autònoma de Barcelona

See the link below for a full copy (there go to Fermilab Library Server).
Status: defended (03/03/2006)
Student: Eva Domingo-Santamaria
Supervised by: Cortina, J.; Diego F. Torres
University: Universitat Autònoma de Barcelona

See the link below for a full copy (there go to Fermilab Library Server).
Institute of Space Sciences (IEEC-CSIC)

Campus UAB, Carrer de Can Magrans, s/n
08193 Barcelona.
Phone: +34 93 737 9788
Email: ice@ice.csic.es
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