Finalized PhD theses

Number of entries: 82

GNSS-R as a Source of Opportunity for Remote Sensing of the Cryosphere

Status: defended (13/05/2013)
Student: Fran Fabra Cervellera
Supervised by: Estel Cardellach Galí
University: Universitat Politècnica de Catalunya

This work evaluates the potential use of signals from the Global Navigation Satellite Systems (GNSS) that scatter off the Earth surface for the retrieval of geophysical information from the cryosphere. For this purpose, the present study is based on data collected with a dedicated reflectometry GNSS…
Status: defended (13/05/2013)
Student: Fran Fabra Cervellera
Supervised by: Estel Cardellach Galí
University: Universitat Politècnica de Catalunya

This work evaluates the potential use of signals from the Global Navigation Satellite Systems (GNSS) that scatter off the Earth surface for the retrieval of geophysical information from the cryosphere. For this purpose, the present study is based on data collected with a dedicated reflectometry GNSS receiver during two field campaigns, which were focused on two types of characteristic surfaces of the cryosphere: thin sea ice covers and thick dry snow accumulations. During the first experiment, the complete process of formation, evolution and melting of sea ice was monitorized for more than seven months in a bay located in Greenland. This type of ice is typically characterized by its thickness, concentration and roughness. Different observables from GNSS reflections are analyzed to try to infer these properties. The ice thickness is linked to the free-board level, defined as the height of the sea ice
surface. Accurate phase altimetry is achieved, showing good agreement with an Arctic tide model. In addition, the long term results of ellipsoidal height retrievals are consistent with the evolution of the ice surface temperature product given by MODIS, which is a key parameter in the rate of growth of sea ice. On the other hand, the presence of salinity in the sea ice modifies its dielectric properties, resulting in different amplitude and phase for the co- and cross-polar components of the complex Fresnel coefficients. The polarimetric measurements obtained show good agreement with visual inspections of ice concentration from an Arctic weather station. Finally, the shape of the reflected signals and its phase dispersion are tested as potential signatures of surface roughness. For comparison, ice charts of the experimental area are employed. In particular, maximums in roughness given by the GNSS observables coincide with fast ice events. Fast ice is defined as ice anchored to the coast, where the tidal movements contribute to the development of strange patterns, cracks, and fissures on its surface, thus consistent with the GNSS-R roughness retrievals. The second experiment took place on Antarctica, monitoring a pristine snow area which is well-known for the calibration of remote sensing instruments. Due to the relative stability of the snow layers, the data acquisition was limited to ten continuous days. Interferometric beats were found after a first analysis of the amplitude from the collected signals, which were consistent with a multipath model where the reflector lies below the surface level. Motivated by these results, a forward model is developed that reconstructs the complex received signal as a sum of a finite number of reflections, coming from different snow layers (a snow density profile obtained from in-situ measurements). The interferometric information is then retrieved from the spectral analysis applied to time series from both real and modeled signals (lag-holograms). We find that the frequency bands predicted by the model are in general consistent with the data and the lag-holograms show repeatability for different days. Then, we attempt a proper inversion of the collected data to determine the dominant layers of the dry snow profile that contribute to L-band reflections, which are related to significant gradients of snow density/permittivity.

A search for low-mass objects in young star-forming regions

Status: defended (12/04/2013)
Student: Manuel Perger
Supervised by: Martín, E.; Barrado y Navascues, D.

The best tool to characterize the formation of stars is the mass function. The members of the young and nearby Taurus star-forming region represent an important exception to the universal form of the function since many low-mass objects would be missing in this low-density region in order to match its…
Status: defended (12/04/2013)
Student: Manuel Perger
Supervised by: Martín, E.; Barrado y Navascues, D.

The best tool to characterize the formation of stars is the mass function. The members of the young and nearby Taurus star-forming region represent an important exception to the universal form of the function since many low-mass objects would be missing in this low-density region in order to match its universal form.
We aimed to find new members of Taurus. To this end, we investigated the area located 5 deg north of the main clouds. To probe the link between the difference of the mass function of Taurus and its low density, we also studied the Orion region. As database for our search we used the wide-field near-infrared photometric survey UKIDSS GCS.  Additionally, we analyzed the photometric characteristics of all 351 already known Taurus members. All in all, we applied around 40 selection criteria. To prove the membership of all selected sources, we observed the candidates with low-resolution optical spectroscopy. In those wavelength ranges, many line features can reveal the youth of a source. To compare them, a set of already known Taurus members and field dwarfs were observed.
In Taurus and Orion, we observed 47 of 272 and 7 of 55 candidates, respectively. The complete photometric and spectral analysis revealed 7 and 4 of them as possible new WTTS members. The new Taurus members are not connected to any molecular cloud and have moved from their birth site to their present location. Their existence indicates a significant unknown population of Taurus members away from the main clouds. We conclude that the missing Taurus low-mass objects are located away from the main clouds of the region. The answer to whether this young and nearby star-forming region is unique or not can be found in its outer parts. The region is beyond doubt of lower density and more stretched out as previously assumed.

Populating cosmological simulations with galaxy using the HOD model

Status: defended (01/02/2013)
Student: Jorge Carretero Palacios
Supervised by: Francisco Javier Castander Serentill; Enrique Gaztañaga
University: Universitat Autònoma de Barcelona

We want to produce galaxy catalogs from N-body dark matter simulations. Those catalogs should be compare to real data and in this way we will learn about the process of galaxy formation.
Populating cosmological simulations with galaxy using the HOD model
Status: defended (01/02/2013)
Student: Jorge Carretero Palacios
Supervised by: Francisco Javier Castander Serentill; Enrique Gaztañaga
University: Universitat Autònoma de Barcelona

Populating cosmological simulations with galaxy using the HOD model

The role of magnetic fields in the formation of low and high mass stars

Status: defended (12/06/2012)
Student: Frau, P.
Supervised by: Josep Miquel Girart Medina; Beltrán, M. T.
University: Universitat de Barcelona

The complex interplay among self-gravity, thermal support, turbulence, rotation, and magnetic fields, and ultimately the observable features that arise from them, are not well characterized observationally and, therefore, not well understood theoretically. The fact that the starless cores are diffuse and cold objects, makes them very difficult of observing because their emission is very faint. Our goal in this work is to deepen into the understanding of the formation, survival and evolution of low-mass dense cores. We doubly face this objective since we aim: Firstly, to characterize observationally the physical and chemical properties of magnetized starless dense cores in the earliest stages of evolution to derive the initial conditions for star-formation, and to check whether the magnetic field is playing a role in the evolution of the cores and; Secondly, to compare observations of more evolved Class 0 sources with models of collapse of magnetized clouds to find the most likely initial conditions and dominant physical processes. In order to achieve the first goal, we have selected a sample of starless cores of the Pipe Nebula. This nearby dark molecular cloud complex has a very low star formation efficiency, which makes it an ideal target to study the properties and evolution of pristine starless dense cores. For the second goal, we have selected NGC 1333 IRAS 4A. It is probably the best studied low-mass protostellar dense core, not only through molecular and dust emission, but also through high angular resolution polarimetric observations of the dust emission.
The complex interplay among self-gravity, thermal support, turbulence, rotation, and magnetic fields, and ultimately the observable features that arise from them, are not well characterized observationally and, therefore, not well understood theoretically. The fact that the starless cores are diffuse…
Status: defended (12/06/2012)
Student: Frau, P.
Supervised by: Josep Miquel Girart Medina; Beltrán, M. T.
University: Universitat de Barcelona

The complex interplay among self-gravity, thermal support, turbulence, rotation, and magnetic fields, and ultimately the observable features that arise from them, are not well characterized observationally and, therefore, not well understood theoretically. The fact that the starless cores are diffuse and cold objects, makes them very difficult of observing because their emission is very faint. Our goal in this work is to deepen into the understanding of the formation, survival and evolution of low-mass dense cores. We doubly face this objective since we aim: Firstly, to characterize observationally the physical and chemical properties of magnetized starless dense cores in the earliest stages of evolution to derive the initial conditions for star-formation, and to check whether the magnetic field is playing a role in the evolution of the cores and; Secondly, to compare observations of more evolved Class 0 sources with models of collapse of magnetized clouds to find the most likely initial conditions and dominant physical processes. In order to achieve the first goal, we have selected a sample of starless cores of the Pipe Nebula. This nearby dark molecular cloud complex has a very low star formation efficiency, which makes it an ideal target to study the properties and evolution of pristine starless dense cores. For the second goal, we have selected NGC 1333 IRAS 4A. It is probably the best studied low-mass protostellar dense core, not only through molecular and dust emission, but also through high angular resolution polarimetric observations of the dust emission.

Star formation ahead of the Herbig-Haro 80N

Status: defended (23/03/2012)
Student: Masqué, J. M.
Supervised by: Josep Miquel Girart Medina; Estalella, R.
University: Universitat de Barcelona

This thesis is focused in the detailed study of the star formation process found ahead of the Herbig-Haro 80N
This thesis aims at probing the influence of protostellar outflows to nearby star forming cores by studying the particular case of the HH 80N core. To do so, we first study the chemical properties of the core in the frame of HH photoillumination. The HH 80N core is larger and more massive than other HH…
Status: defended (23/03/2012)
Student: Masqué, J. M.
Supervised by: Josep Miquel Girart Medina; Estalella, R.
University: Universitat de Barcelona

This thesis aims at probing the influence of protostellar outflows to nearby star forming cores by studying the particular case of the HH 80N core. To do so, we first study the chemical properties of the core in the frame of HH photoillumination. The HH 80N core is larger and more massive than other HH irradiated clumps, and harbors an embedded object, suggesting a different nature for this core. Our first goal is to see if the HH 80N core has a chemistry similar to that observed in other clumps ahead of HH objects. In the following step, we study the physical properties of the HH 80N core in order to look for evidence of the influence of the HH 80/81/80N jet in the star formation process that is taking place in this core. While many studies on triggered star formation are based on the statistics of a large number of objects \citep[e.g.][]{chauhan2011}, in this thesis we focus our study on an isolated star-forming core to find direct evidence of interaction of the HH 80/81/80N outflow with the core.

Focal plane detectors of a Laue lens telescope for Nuclear Astrophysics

Status: defended (31/01/2012)
Student: José Manuel Álvarez Pastor
Supervised by: Margarita Hernanz Carbó
University: Universitat Autònoma de Barcelona

TBW
Status: defended (31/01/2012)
Student: José Manuel Álvarez Pastor
Supervised by: Margarita Hernanz Carbó
University: Universitat Autònoma de Barcelona

TBW

Parallel Post-Processing Solution for GNSS-R Instrument

Status: defended (16/12/2011)
Student: Guo Yi
Supervised by: Antonio Rius Jordán; Ferrer Ramis, Carles
University: Universitat Autònoma de Barcelona

Microelectronica i Sistemes Electrònics
Status: defended (16/12/2011)
Student: Guo Yi
Supervised by: Antonio Rius Jordán; Ferrer Ramis, Carles
University: Universitat Autònoma de Barcelona

Microelectronica i Sistemes Electrònics

The Joan Oró Telescope at the Montsec Astronomical Observatory Solutions for Unattended Operation

Status: defended (10/11/2011)
Student: Josep Colomé Ferrer
Supervised by: Ignasi Ribas Canudas
University: Universitat de Barcelona

El objetivo principal de esta Tesis ha sido la robotización del Telescopio Joan Oró del Observatorio Astronómico del Montsec (TJO-OAdM) para conseguir un sistema con un alto nivel de autonomía y eficiencia. El telescopio robótico TJO-OAdM fue propuesto a mediados de los años 90 y representaba en…
Status: defended (10/11/2011)
Student: Josep Colomé Ferrer
Supervised by: Ignasi Ribas Canudas
University: Universitat de Barcelona

El objetivo principal de esta Tesis ha sido la robotización del Telescopio Joan Oró del Observatorio Astronómico del Montsec (TJO-OAdM) para conseguir un sistema con un alto nivel de autonomía y eficiencia. El telescopio robótico TJO-OAdM fue propuesto a mediados de los años 90 y representaba en ese momento un reto tecnológico para el campo de la instrumentación astronómica. Se concibió como un telescopio multipropósito con una operación completamente desatendida. El desarrollo inicial no cumplió con las expectativas de funcionamiento. Tenía varias deficiencias causadas principalmente por un desarrollo basado en una instrumentación comercial que no era adecuada para un control desatendido y fiable. Y, además, presentaba una incompleta definición de la arquitectura del sistema para garantizar el control de toda la instalación y de todos los procesos incluidos en el flujo de datos. El trabajo de la Tesis se ha focalizado en aplicar los cambios necesarios en el diseño inicial para tener un sistema capaz de dar respuestas inteligentes a cualquier situación así como proporcionar un control desatendido del flujo completo de datos. Las especificaciones incluyen desde la preparación e introducción en el sistema de las propuestas de observación hasta el procesado de los datos y la posterior entrega a los usuarios. El aislamiento del lugar y las condiciones meteorológicas extremas añaden un requerimiento de robustez al desarrollo del sistema. Se considera fundamental, pues, lograr una alta fiabilidad, robustez y calidad de los datos recogidos para maximizar la eficiencia y el retorno científico. La Tesis se estructura en tres bloques principales: el análisis y diseño del sistema, en el que se definen las necesidades y la estructura de control; la fase de desarrollo, en la que se presentan el diseño y la implementación de los módulos hardware y software que forman parte de la arquitectura de control; y el control de calidad, donde se ha realizado un análisis de riesgo y se han aplicado metodologías de verificación y validación para garantizar que el sistema final cumplía con los requerimientos iniciales.

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).
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