Finalized PhD theses

Number of entries: 84

Simulations of extreme-mass-ratio inspirals in the LISA frequency band

Status: defended (21/10/2011)
Student: Priscilla Canizares Martinez
Supervised by: Carlos Sopuerta ; José Alberto Lobo Gutiérrez
University: Universitat Autònoma de Barcelona

LISA, the Laser Interferometer Space Antenna, is a joint mission between the European Space Agency and the National Aeronautics and Space Administration (USA) scheduled to fly in about 10 years. Its primary scientific goal is to carry out low-frequency gravitational wave astronomy, opening in this way a completely new window to the exploration of the universe that is expected to lead to dramatic discoveries in astrophysics and cosmology, as well as tests of the validity of general relativity. The inspiral, driven by gravitational radiation emission, of compact objects into (super)massive black holes sitting at the galactic centers [known as extreme-mass-ratio inspirals (EMRIs)] is one of the main LISA targets. The main goal of this research is to design and produce simulations of EMRIs and obtain precise theoretical gravitational waveforms of the inspiral. These waveforms are crucial in order to extract the signals produced by EMRIs, which will be buried in instrumental noise and the gravitational wave foreground, and later extract relevant physical information from them. To carry these simulations one needs to use perturbative general relativity and the modern techniques for the estimation of the gravitational backreaction.
Extreme-Mass-Ration Inspirals (EMRIs) are astrophysical systems made up of a Stellar-mass Compact Object (SCO) and a Massive Black Hole (MBH). When the SCO is captured by the MBH, it performs highly eccentric and relativistic orbits, which gradually shrink and circularise due to the emission of gravitational…
Status: defended (21/10/2011)
Student: Priscilla Canizares Martinez
Supervised by: Carlos Sopuerta ; José Alberto Lobo Gutiérrez
University: Universitat Autònoma de Barcelona

Extreme-Mass-Ration Inspirals (EMRIs) are astrophysical systems made up of a Stellar-mass Compact Object (SCO) and a Massive Black Hole (MBH). When the SCO is captured by the MBH, it performs highly eccentric and relativistic orbits, which gradually shrink and circularise due to the emission of gravitational waves (GW). In order to obtain all the physical information carried by the GWs, we will need to know how to model these kinds of systems. That in practice means to compute the gravitational self-force that drives the inspiral of the SCO. On the other hand, since the SCO orbit depends upon the MBH geometry, EMRIs are an invaluable tool to test alternative theories of gravity. In this talk, we are going to review the gravitational self-force problem and we will see the main points of the new numerical technique that we propose to compute it. Moreover, we are going to see how LISA may test alternative theories of gravity from EMRI detections, mainly the role that self-force will play in the distinction between General Relativity and an alternative theory of gravity like Chern-Simons.

X-rays emission from accreting white dwarfs in post-outburst novae

Status: defended (27/07/2011)
Student: Carlo Ferri
Supervised by: Margarita Hernanz Carbó
University: Universitat de Barcelona

To be included shortly
Thanks to launch of XMM-Newton and Chandra, and more recently Swift satellite, the number of post-outburst novae detected in X-rays has increased considerably in the last years. Some puzzling results concerning the SSS phase duration, the reestablishment of accretion process and the temporal behavior…
Status: defended (27/07/2011)
Student: Carlo Ferri
Supervised by: Margarita Hernanz Carbó
University: Universitat de Barcelona

Thanks to launch of XMM-Newton and Chandra, and more recently Swift satellite, the number of post-outburst novae detected in X-rays has increased considerably in the last years. Some puzzling results concerning the SSS phase duration, the reestablishment of accretion process and the temporal behavior have been discovered, providing new insights into the diversity and the evolution of such systems. The present thesis work has been aimed to perform a comprehensive study both in X-ray and optical bands of post-outburst classical novae, particularly Nova Oph 1998 (V2487 Oph) and Nova Cyg 2006 (V2362 Cyg). High resolution spectra and timing information of XMM-Newton and optical ground-based observations have been analized to estimate the basic parameters of the emitting region from these classical novae. This has made it possible to improve the determination of the thermal plasma component parameters (temperature, density) responsible for the Xray emission, to disentangle if there are additional contributions to this emission (e.g. reflection), and to determine the physical properties of the plasma (accreting flow and/or ejecta). In addition timing analysis provided information about periodicities (orbital and rotational) of the binary systems and, therefore, about the nature of the underlying cataclysmic variable (non-magnetic or magnetic, with synchronous or non-synchronous rotation).

Some theoretical and observational aspects on cosmic-ray diffusion

Status: defended (22/07/2011)
Student: de Cea del Pozo, E.
Supervised by: Diego F. Torres
University: Universitat Autònoma de Barcelona

TBD
Status: defended (22/07/2011)
Student: de Cea del Pozo, E.
Supervised by: Diego F. Torres
University: Universitat Autònoma de Barcelona

TBD

On Friedmann-Lemaître-Robertson-Walker cosmologies in non-standard gravity

Status: defended (31/03/2011)
Student: Diego Sáez-Chillón Gómez
Supervised by: Emilio Elizalde ; Sergei D Odintsov
University: Universitat de Barcelona

The main aim of this work is to show how different approaches could resolve the problem of dark energy and model the entire evolution of Universe history, from inflation to the current epoch. The different answers and intrinsic questions related to each model have been analyzed, as none of them is free…
Status: defended (31/03/2011)
Student: Diego Sáez-Chillón Gómez
Supervised by: Emilio Elizalde ; Sergei D Odintsov
University: Universitat de Barcelona

The main aim of this work is to show how different approaches could resolve the problem of dark energy and model the entire evolution of Universe history, from inflation to the current epoch. The different answers and intrinsic questions related to each model have been analyzed, as none of them is free of its proper unresolved questions. The possibility to distinguish between different theories is discussed, where the observations as well as possible predictions have to play a fundamental role.

Magnetic fields in star-forming regions: a multi-wavelength approach

Status: defended (03/03/2011)
Student: Felipe Alves
Supervised by: Josep Miquel Girart Medina
University: Universitat de Barcelona

The goal of my thesis is centered in using polarimetry as main tool to study star forming regions. Data obtained in a wide range of wavelengths provide information about the physical processes involved in the formation of star at different scales. In particular, I'm interested in the morphology of the magnetic field and how it varies from molecular clouds (physical scales of a few parsecs) down to protostellar cores (several AU's). I use optical and near-infrared data to derive the field at larger scales, and millimeter/sub-millimeter wavelengths for core scales. It's observed that the field morphology can be significantly distinct in different cases, having a very uniform component for some magnetized clouds (like the Pipe Nebula) or a less ordered field under effects of turbulence. In the mm/submm range, the case of NGC 2024 FIR 5 is being used to test observationally star-forming models. The magnetic field in this core has a partial hourglass geometry, which is proposed by models of ambipolar diffusion or can be disturbed by an ionization front which is expanding close to it. In a general aspect, I'm performing a comparative investigation of the magnetic field morphology for different scales.
The science case of this thesis is focused in the study of the role of the interstellar magnetic field in the star formation process at different physical scales. This study is connected with the gas dynamics at distinct density components. For this purpose, an extensive observational work using distinct…
Status: defended (03/03/2011)
Student: Felipe Alves
Supervised by: Josep Miquel Girart Medina
University: Universitat de Barcelona

The science case of this thesis is focused in the study of the role of the interstellar magnetic field in the star formation process at different physical scales. This study is connected with the gas dynamics at distinct density components. For this purpose, an extensive observational work using distinct astronomical facilities was performed. A multi-scale picture is achieved when distinct magnetic field tracers are used. With this technique, the research described in this thesis aims to study the evolution of astrophysical objects based on their magnetic field morphology. Star-forming theories predict that both quantities are closely related, so the thesis goal is to search for observational evidences for those models. In a more general aspect, this investigation aims to provide an heterogeneous polarization database for molecular clouds at distinct evolutionary stages.

Massive Star Formation: ionized and molecular gas emission in the first evolutionary stages

Status: defended (25/02/2011)
Student: Sánchez-Monge, Álvaro
Supervised by: Dr. Robert Estalella; Dr. Stan Kurtz; Dr. Aina Palau
University: Universitat de Barcelona

First stages of massive star formation not well understood yet. With the goal of studying the relation between the ionized and molecular gas components we have observed with high angular resolution the ionized gas and molecular emission, together with dust continuum emission, of 6 massive star-forming…
Status: defended (25/02/2011)
Student: Sánchez-Monge, Álvaro
Supervised by: Dr. Robert Estalella; Dr. Stan Kurtz; Dr. Aina Palau
University: Universitat de Barcelona

First stages of massive star formation not well understood yet. With the goal of studying the relation between the ionized and molecular gas components we have observed with high angular resolution the ionized gas and molecular emission, together with dust continuum emission, of 6 massive star-forming regions. These data, together with similar data from the literature for 4 additional sources, allow us to search for correlations between the ioniozed and molecular gas components. We find that the sample can be divided into two groups. The most evolved sources, typically showing flat spectral indices in the centimeter range and not well associated with molecular gas, and the youngest sources, showing steep spectral indices in the centimeter range and being well associated with molecular gas, tracing hot core emission, and driving outflows. Some hints of a possible relation between the rotational temperature derived from NH3 and the bolometric luminosity, as well as the collimation factor and the momentum flux and the bolometric luminosity are presented.

Chemical and Dynamical Galaxy Evolution

Status: defended (16/11/2010)
Student: Artigas A.
Supervised by: Isern J.; Bravo E.

Using Smoothed Particle Hydrodynamics simulations (Gadget-2 code) we explore the evolution of an individual galaxy. In the code we have included gas cooling, star formation, gas and metal restitution from dying stars plus supernovae energy and chemical feedback (SNII and SNIa). All the ingredients have been treated statistically thus a high resolution is needed in order to achieve good results. We follow the formation and evolution of a disk-like galaxy, predict the final structure and metallicity evolution.
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Status: defended (16/11/2010)
Student: Artigas A.
Supervised by: Isern J.; Bravo E.

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Evolució quimiodinàmica de la Galàxia

Status: defended (16/11/2010)
Student: Anna Artigas
Supervised by: Jordi Isern Vilaboy
University: Universitat de Barcelona

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Status: defended (16/11/2010)
Student: Anna Artigas
Supervised by: Jordi Isern Vilaboy
University: Universitat de Barcelona

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The effect of activity on the fundamental properties o low-mass stars

Status: defended (14/06/2010)
Student: Morales, J.C.
Supervised by: Ignasi Ribas Canudas; Jordi, C.
University: Universitat de Barcelona

Recent analyses of eclipsing binaries suggest a significant discrepancy between the observed radii of low-mass stars in binary systems and the predictions of theoretical models. This stands in contrast with the fact that theory now provides excellent agreement with the observed radii of low mass stars, either single or in wide binary systems. The observed disagreement for stars in close binary systems be associated with the generally strong magnetic activity of stars in close binaries caused by their relatively fast rotation rates. The project of this PhD thesis is to study and resolve the discrepancies by analyzing additional eclipsing binaries and modifying current stellar models to incoporate the effects of magnetic fields.
La comparación entre los modelos de estructura estelar y las observaciones de estrelles de baja masa, indican que los radios y temperaturas efectivas que predicen los modelos son aproximadamente un 10% más pequeños y un 5% más altas, respectivamente, que las observaciones. Las estrellas binarias…
Status: defended (14/06/2010)
Student: Morales, J.C.
Supervised by: Ignasi Ribas Canudas; Jordi, C.
University: Universitat de Barcelona

La comparación entre los modelos de estructura estelar y las observaciones de estrelles de baja masa, indican que los radios y temperaturas efectivas que predicen los modelos son aproximadamente un 10% más pequeños y un 5% más altas, respectivamente, que las observaciones. Las estrellas binarias eclipsantes han demostrado ser una herramienta muy útil para testear estos modelos ya que permiten obtener las masas y radios de la estrellas con precisiones del orden del 2%. En este trabajo, se han obtenido las propiedades fundamentales de los sistemas binarios CM Draconis e IM Virginis. La comparación conjunta de estos sistemas, junto con otros con propiedades muy bien determinadas, se ha utilizado para testear los modelos de estructura estelar. Los resultados indican que la actividad magnética presente en estos sistemas es la causante de las diferencias entre los modelos y las observaciones, por su efecto sobre el transporte convectivo en el interior de las estrellas y por la aparición de manchas en su superficie.

Design and evaluation of navigation and control algorithms for spacecraft formation flying missions

Status: defended (21/05/2010)
Student: Laura Perea Virgili
Supervised by: Pedro Elosegui Larrañeta
University: Universitat de Barcelona

Formation flying offers space-dependent disciplines such as astrophysics, astrodynamics, and geodesy, to name a few, the possibility of creating large spaceborne sensors from an array of small spacecraft flying in formation. This creates exciting scientific and technical opportunities as the formation…
Status: defended (21/05/2010)
Student: Laura Perea Virgili
Supervised by: Pedro Elosegui Larrañeta
University: Universitat de Barcelona

Formation flying offers space-dependent disciplines such as astrophysics, astrodynamics, and geodesy, to name a few, the possibility of creating large spaceborne sensors from an array of small spacecraft flying in formation. This creates exciting scientific and technical opportunities as the formation could be arranged to work as, for example, an interferometer, thus providing a most unlimited angular resolution or a virtual telescope, thus unrestricted focal distances. Since the first mission including formation flying technology (EO-1) was selected by NASA, some of the challenges to realize full Formation Flying (FF) capabilities has been thought to be the definition of suitable algorithms to navigate and control FF missions. The focus of this dissertation is the design and evaluation of algorithms for navigation and control for formation flying missions. Given its importance, extensive research has been already conducted to fulfill the increase of accuracy, autonomy, and other requirements of the Guidance, Navigation, and Control (GNC) systems that derive from novel applications of formation flying missions. To center the scope of present work, we have mainly focused in three of the present challenges: the difficulties of fusing different non-linear observations for relative navigation; the analysis and extension of behavioral algorithms for controlling a formation of spacecraft; and the design and validation of a control law for formation acquisition and formation keeping of a non-natural relative trajectory. These three interconnected topics cover a wide range of research in formation flying and embody the main algorithm components of formation flying algorithms from the observations to the navigation and to the control. The first challenge consisted, thus, in addressing the difficulties encountered by classical filters to estimate a state vector fusing common observations. We proposed several strategies to improve the robustness of these filters under non-linear conditions. Among these strategies, the modification of the residuals computation for the Unscented Kalman Filter (UKF) deserves special mention due to its excellent results and robustness against nonlinearities. A theoretical basis for these results became, thus, necessary regarding the new update equation of the UKF and has been developed subsequently in the frame of this thesis. This work has been published in Perea et al. (2007) and Perea and Elosegui (2008). The collective motion exhibited by some groups of animals has recently attracted the interest of many research groups who try to take advantage of the robustness and efficiency of natural patterns. With this aim, we have investigated the possibility of extending an interaction model that has shown emergent behavior. In particular, the Cucker-Smale (CS) model has been extended for its application on spacecraft formation flying. Numerical simulations of the Darwin mission have proved that this strategy is suitable for loose formation keeping. Of special relevance is the low cost of the controller, specially compared to an alternative strategy, the Zero Relative Radial Acceleration Cones (ZRRAC). The problem of tight formation keeping is addressed previous publications. In these papers, we first study the relative dynamics of a virtual telescope that follows a non-natural relative trajectory driven by the position of an observed body and not by the natural forces in space. This analysis has originated the design of several controls based on different approximations of the relative dynamics. Their performances have been tested and compared through numerical simulations of the PROBA-3 mission using, first, computer based simulations, and then, a realistic platform with GNSS hardware and operational flight software in the loop. The main conclusions show that simple control definitions, as defined by the Linear Quadratic Regulator (LQR) and Linear Quadratic Regulator with the Integral term (LQRI), can fulfill stringent requirements for formation acquisition and tight formation keeping. (Formation flying is a key, forthcoming technology with an ever increasing number of applications in space missions. This thesis faces some of the present challenges in specific navigation and control algorithms for formation flying missions: nonlinear data fusion in navigation filters; loose controls based on natural patterns; and tight controls to keep non-natural relative trajectories. The proposed algorithms have been tested under the Darwin and PROBA-3 scenarios in realistic platforms.)
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An institute of the Consejo Superior de Investigaciones Científicas
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