Adaptive optics (AO) systems are used to increase the spatial resolution achieved by ground-based telescopes, which are limited by the atmospheric motion of air layers above them. Therefore, the real cut-off frequency is extended closer to the theoretical diffraction limit of the telescope thus allowing more high-frequency information from the object to be present in the image. Nevertheless, although the goal of image reconstruction and deconvolution algorithms is basically the same (i.e., to recover a “real” diffracted limit image, free of noise, from the object), and since the correction of AO is not complete (i.e., the effective cut-off frequency achieved by AO is still below the theoretical diffraction limit), the simultaneous use of such deconvolution algorithms over dataset acquired with AO is possible and desirable to further enhance their contrast. On the other hand, multiresolution tools like the wavelet transform (WT) have been historically introduced into multiple deconvolution schemes improving their performance with respect to their non-wavelet counterparts. The ability of such transforms to separate image components depending on their frequency content results in solutions that are generally closer to the real object. On the other hand, AO community generally states that, due to the high variability of AO PSFs is necessary to update the PSF estimate during the reconstruction process. Hence, the use of blind and myopic deconvolution algorithms should be unavoidable and yields to better results than those obtained by the static-PSFs codes. Therefore, being the aforementioned paragraphs the current state-of-art of AO imaging, this thesis yields the following topics/goals: 1. The static-PSF algorithm AMWLE has been applied over binary systems simulated for the 3-m Shane telescope to evaluate the photometric accuracy of the reconstruction. Its performance is compared with the PSF-fitting algorithm StarFinder, commonly used by the AO community, as well as other algorithms like FITSTAR, PDF deconvolution and IDAC. Results shown that AWMLE is able to produce better results than StarFinder and FITSTAR, and very similar results with respect to the rest of codes, especially for high Strehl ratios (SR) and matched PSFs. 2. A new deconvolution algorithm called ACMLE, based on the curvelet transform (CT) and a maximum likelihood estimator (MLE), has been designed for the reconstruction of extended and/or elongated objects. ACMLE has been tested together with AMWLE and blind/myopic codes such as MISTRAL and IDAC over Saturn and galaxy simulated images for the 5-m. Hale telescope. It is shown that the performance in the presence of noise of the multiresolution static-PSF algorithms is better than myopic and blind algorithms, thus showing that the control of noise is as important as the update of the PSF estimate during the reconstruction process. 3. A unidimensional WT has been applied in the spectral deconvolution of integral field spectroscopy (IFS) datacubes for direct imaging of exoplanets with EPICS instrument, which will be installed at the forthcoming 39-m E-ELT telescope. When this approach is compared with the classical non-wavelet one, an improvement of 1 mag from angle separations equal to 73 mas is devised. Furthermore, detection of close-in planets, between 43 and 58 mas also benefit of the application of wavelets. The use of WT allows the APLC chronograph to obtain similar results with respect to the apodizer-only solution, especially with increasing Talbot length, thus showing that WT classify planet frequency components and chromatic aberrations in different scales. Preliminary results for HARMONI spectrograph are also shown. This thesis opens several lines of research that will be addressed in future: - The world of multiresolution transforms is extremely huge and has produced dozens of new mathematical tools. Among many other, it is worthwhile to mention the shearlet transform, which is an extension/improvement of CT, and the waveatom tool, which is intended to classify textures in the image. They should be studied and compared to establish their best performance and their best field of application over AO images. - Blind and myopic algorithms have proved their ability for large mismatches between the “real” PSF that has created the image and the PSF that is used as a first estimate in the reconstruction process. However, their performance in the presence of noise is highly affected. Hence, it is convenient to investigate if it is possible to introduce (and how to do it) multiresolution transforms into these algorithms to improve their behavior. - For the study of IFS datacubes, other father scaling functions with different shapes could be proposed, in particular, it can be considered a “dynamic” scaling function with the ability to modulate its shape according to the low frequency signal to be removed from the spaxel. This could potentially improved the final photometry of the detected faint source. Besides, the design of a dictionary of wavelets, which increase the decomposing resolution across the spaxel, instead of a single dyadic decomposition, can improve the photometric accuracy of detected planets as well as their spectral characterizations, taking full advantage of the information contained in the IFS datacubes.

En la tesis, proponemos usar el estudio de la agrupación de las galaxias, en particular usando correlaciones cruzadas angulares, para entender la etapa tardía de expansión del Universo y el crecimiento de estructura a gran escala. Los cartografiados extragalácticos miden la posición de las galaxias (que son trazadores del campo de materia oscura) en coordenadas esféricas (z,θ,φ). Muchos análisis de la distribución de galaxias convierten estas coordenadas en distancias, asumiendo una cosmología. Este tipo de análisis requiere rehacer todo el análisis de las medidas para cada modelo cosmológico con el que se quiera comparar. Como alternativa, proponemos seleccionar las galaxias en intervalos radiales, de acuerdo a la medida de sus desplazamientos de longitud de onda al rojo, z, para posteriormente analizar las correlaciones angulares (2D) en cada intervalo. Mediante esta manera de abordar el análisis se pierde información 3D a lo largo de la línea de visión, para escalas menores que la anchura de cada intervalo. Pero evitamos tener que asumir un modelo cosmológico de partida. Hemos visto que un análisis basado en funciones angulares de correlación cruzadas entre diferentes intervalos puede recuperar los modos radiales correspondientes a separaciones dadas por la distancia entre bines. La división en intervalos óptima para recuperar la información 3D viene dada por la escala mínima considerada en el análisis espacial, 2π/kmax, y por la escala dada por el error en el z fotométrico. Los cartografiados extragalácticos fotométricos, como Physics of the Accelerating Universe (PAU) y el Dark Energy Survey (DES), nos permiten acceder a mayores densidades de galaxias y a zonas más profundas del Universo que las alcanzadas en los cartografiados espectroscópicos actuales., pero perdiendo resolución radial. El análisis angular en distintos intervalos es la manera natural de analizar este tipo de cartografiados. Hemos visto que, para este tipo de cartografiados, la determinación del índice de crecimiento de estructura mejora un factor dos si incluimos las correlaciones cruzadas. Además, mostramos que si usamos dos poblaciones de galaxias como trazadores de materia oscura reducimos la varianza cósmica. Usando las correlaciones entre ambas poblaciones en el mismo área, los resultados mejoran un factor cinco. Esto nos permite determinar a un 10% el crecimiento de estructuras para z>1, lo que nos permite complementar los resultados a bajo z obtenidos mediante espectroscopía. La ganancia se magnifica para trazadores que se agrupen de manera muy diferente y con alta densidad. Hemos usado simulaciones de N-cuerpos para incluir efectos no lineales, de manera que podemos activarlos o desactivarlos (como las distorsiones en el espacio de z o las debidas a z fotométricos). Se han construido catálogos a partir de las simulaciones MICE para medir el agrupamiento en la distribución de galaxias, comparándolo con los modelos teóricos de las correlaciones angulares. Hemos hallado una buena correspondencia entre ambos. Los planes futuros pasan por utilizar esta metodología para la estimación de parámetros cosmológicos, particularmente para DES y PAU. / In this thesis we propose to use galaxy clustering, more concretely angular cross-correlations, as a tool to understand the late-time expansion of the Universe and the growth of large-scale structure. Galaxy surveys measure the position of galaxies (what traces the dark-matter field) in spherical coordinates (z,θ,φ). Most galaxy clustering analyses convert these positions to distances assuming a background cosmology. This approach thus requires doing the full data analysis for each background cosmological model one wants to| test. Instead we propose to select galaxies in radial shells, according to their redshifts, and then measure and analyze the angular (2D) correlations in each bin circumventing the model assumption. On the one hand our approach projects and looses 3D information along the line-of-sight for distances smaller than the shell width. On the other hand, it allows a single analysis, as no cosmological model needs to be assumed. Remarkably we find that if we include in the analysis also the angular cross-correlations between different shells, we can recover the radial modes corresponding to the separations between radial bins. We found that the optimal binning to recover 3D information is given by the largest between the minimum scale considered for spatial clustering, 2π/kmax, and the photometric redshift error. Photometric galaxy surveys, such as Physics of the Accelerating Universe (PAU) and Dark Energy Survey (DES), access higher number densities and higher redshifts than current spectroscopic surveys, at the price of loosing radial accuracy. Angular analysis in redshift bins is then the natural framework for such surveys. We found that, for such photometric surveys, the constraints on the growth index of structure improve by a factor two when we include the cross-correlations. In addition, we show that one can use two different galaxy populations to trace dark matter and hence reduce sample variance errors. The cross-correlations of both populations in the same field leads to an overall gain of a factor five. This allows measurements of the growth rate of structure to a 10% error at high redshifts, z > 1, complementing low-z results from spectroscopic surveys. This gain is maximized for high bias difference and high densities. We also worked with N-body simulations to include non-linear gravitational effects and turn them on and off (e.g redshift space distortions or the radial distortions produced by photometric redshifts). We built galaxy survey mocks from the MICE simulations and measure galaxy clustering to compare with our previously mentioned models of angular correlations. We found a good agreement between theory and simulation measurements. In the future, we expect to apply this framework for cosmological parameter estimation, especially focusing on DES and PAU surveys.

La luz de fondo extragalactica (LFE) es la acumulación de toda la luz producida en la historia del Universo. Las longitudes de onda de esta luz de fondo van desde la banda UV hasta el cercano y lejano infrarrojo. La LFE interactúa con los rayos gamma provenientes de núcleos de galaxias activos (NGA) produciendo pares electrón-positrón. Esto causa que los espectros de energía diferencial de los NGAs observados en la Tierra, en el rango de energía de los rayos gamma, estén modificados por la interacción con la LFE. Este trabajo esta enfocado a las observaciones y el análisis de datos de dos NGAs: Markarian 421 y 1ES 1011+496. Estas dos fuentes fueron observadas en estados de llamaradas extraordinarias por los telescopios MAGIC, proveyendo espectros de buena calidad a muy altas energías. De estas observaciones, el efecto de la LFE en los espectros observados pudo ser medido. Las mediciones fueron realizadas un método de maximización de probabilidad, donde el espectro intrínseco de la fuente es modelado usando una función convexa y suave, modificada por el efecto de la LFE (usando un modelo como plantilla) cuya intensidad es regulada usando un factor de normalización de opacidad. Entonces una exploración es realizada sobre los factores de normalización para encontrar la combinación de parámetros del modelo del espectro intrínseco y el LFE que den la máxima probabilidad de reproducir el espectro observado. Al final, la máxima probabilidad es comparada con la probabilidad de la hipótesis de LFE nula por medio de una prueba de razón de probabilidades. Con este método fue encontrado que con los datos de 1ES 1011+496, el modelo de LFE usado en este trabajo (de Domínguez et al., 2011) escalado por el factor de normalización de opacidad 1.07 (-0.13+0.09)stat (-0.10.+0.7)syst fue preferido sobre la hipótesis de LFE nula con una significancia de 4.6 desviaciones estandar. En el caso de Markarian 421, se encontró que la plantilla de LFE escalada por un factor de normalización de opacidad 0.90 (-0.17+0.11)stat (-0.00+0.29)syst fue preferido sobre la hipótesis de LFE nula con una significancia de 5.8 desviaciones estándar. Análisis adicionales fueron realizados de datos de 1ES 0229+200 y 1ES 0647+250. No se pudieron extraer mediciones del LFE de las observaciones de estas dos fuentes. También en este trabajo se presenta un breve estudio de posibles anomalías en la propagación de los rayos gamma en el medio intergaláctico, causado por la teorética partícula parecida al axion. / The extragalactic background light (EBL) is the collection of all the light produced in the history of the Universe. The wavelength of this background light goes from the UV-optical band to the near- and far-infrared. The EBL interacts with the gamma rays coming from active galactic nuclei (AGN) producing electron-positron pairs. This causes that the differential energy spectra observed at Earth from the AGNs, in the energy range of gamma rays, are modified by the interaction with the EBL. This works is focused in the observations and the data analysis from two AGNs: Markarian 421 and 1ES 1011+496. These two sources were observed in extraordinary flaring states by the MAGIC telescopes, providing good quality expectra at very high energies. From these observations, the effect of the EBL on the observed spectra could be measured. The measurements were performed using a likelihood maximization method, where the intrinsic spectrum of the source is modeled using a smooth convex function, modified by the effect of the EBL (from a model template) whose intensity is regulated using an opacity normalization factor. Then a scan is performed over the normalization factor to find the combination of parameters from the model for the intrinsic spectrum and the EBL that give the maximum likelihood to the observed spectrum. At the end, the maximum likelihood is compared with the likelihood of the null-EBL hypothesis with a likelihood ratio test. With this method it was found that with the data from 1ES 1011+496, the EBL model used in this work (by Dominguez et al. 2011) escaled by an opacity normalization factor of 1.07 (-0.13+0.09)stat (-0.10.+0.7)syst was prefered over the null-EBL hypothesis with a significance of 4.6 standard deviations. In the case of the data from Markarian 421, it was found that the EBL template scaled by the opacity normalization factor of 0.90 (-0.17+0.11)stat (-0.00+0.29)syst was prefered over the null-EBL hypothesis with a significance of 5.8 standard deviations. Additional analyses were performed of data from 1ES 0229+200 and 1ES 0647+250. No EBL measurements could be extracted from the observations of these two sources. Also in this work is presented a brief study of possible anomalies in the propagation of the gamma rays in the intergalactic medium caused by the theoretical axion-like particle.

We explore the possibility of detecting and characterising the warp of the stellar disc of our Galaxy using synthetic Gaia data and two available proper motion catalogues namely UCAC4 and PPMXL. We develop a new kinematic model for the galactic warp. With Gaia, the availability of proper motions and, for the brightest stars radial velocities, adds a new dimension to this study. A family of Great Circle Cell Counts (GC3) methods is used. They are ideally suited to find the tilt and twist of a collection of rings, which allow us to detect and measure the warp parameters. To test them, we use random realisations of test particles which evolve in a realistic Galactic potential warped adiabatically to various final configurations. In some cases a twist is introduced additionally. The Gaia selection function, its errors model and a realistic 3D extinction map are applied to mimic three tracer populations: OB, A and Red Clump stars. We show how the use of kinematics improves the accuracy in the recovery of the warp parameters. The OB stars are demonstrated to be the best tracers determining the tilt angle with accuracy better than ∼ 0.5 up to galactocentric distance of ∼ 16 kpc. Using data with good astrometric quality, the same accuracy is obtained for A type stars up to ∼ 13 kpc and for Red Clump up to the expected stellar cut-off. Using OB stars the twist angle is recovered to within < 3◦ for all distances. In this work we have developed a first and simplified kinematic model for our Galactic warp. The simplicity of the model has allowed us to evaluate the efficacy and limitations of the use of Gaia data to characterise the warp. These limitations have been fully explored and quantified. From the work done so far, we expect that the Gaia database, together with the methods presented here, will be a very powerful combination to characterise the warp of the stellar disc of our Galaxy. Moreover, We introduce LonKin methods that help us detect the kinematic signature of the warp in the vertical motions of stars as a function of galactic longitude. Applying this method to the UCAC4 proper motions, we do not obtain a similar trend as the one we expect from our warp model. We explore a possible source of this discrepancy in terms of systematics caused by a residual spin of the reference frame with respect to the extra- galactic inertial one. We also look into a deeper proper motion survey namely the PPMXL. The effect of systematics in this catalogue was reduced using hundreds of thousand quasars present in this survey. An analytical fit to the vertical velocity trend of red clump stars suggests a vertical oscillation in the southern warp with a rather high frequency that tends to decrease the amplitude of the warp. We analysed this trend in the context of our warp model and an abrupt decrease of the warp’s amplitude in a very short time of about one hundred Myr could explain this trend. / En aquesta tesi volem avaluar la capacitat de diversos mètodes estadístics de identificar i caracteritzar la curvatura del disc estel·lar de la Galàxia en la era de Gaia. Per a portar a terme aquests objectius hem desenvolupat expressions analítiques pel camp de forces d’un potencial tipus Miyamoto-Nagai de disc corbat. Partint del potencial galàctic axisimètric de Allen i Santillan (1991) procedim a distorsionar el potencial d’acord amb dos models diferents de curvatura: 1) un model amb la línia de nodes recta i 2) un model amb que presenta una torsió a mesura que augmenta el radi galactocèntric. Hem generat diversos catàlegs simulats de partícules test on hem anat corbant el potencial del disc bé adiabàticament o impulsiva i als que hem aplicat les limitacions observacionals de Gaia i els models d'error astromètrics esperats. A continuació hem utilitzat mètodes estadístics anomenats Great Circle Cell Counts (GC3) i els hem aplicat a mostres d’estrelles per les quals disposem de la informació en l’espai sis dimensional de posicions i velocitats o només informació en posició. A més, hem introduït d'altres mètodes que analitzen directament la tendència del moviment vertical mig de les estrelles en funció de la longitud galàctica. Demostrem que podem recuperar bé els paràmetres de la mostra d’estrelles OB amb bons paràmetres astromètrics a la que hem imposat una inclinació i una torsió al potencial donada. Els valors es recuperen amb un error inferior 3 graus per a totes les distàncies. És important esmentar que en tots els treballs amb els mètodes GC3 sempre hem utilitzat les paral·laxis trigonomètriques (mai les distàncies). També hem buscat la traça cinemàtica de la curvatura del disc en els catàlegs de moviments propis actualment disponibles, UCAC4 i PPMXL. Constatem la necessitat de conèixer amb bona precisió la rotació residual del sistema de referència respecte al sistema inercial, així com qualsevol altre efecte sistemàtic en els moviments propis. Els nostres resultats amb el catàleg PPMXL mostren que un decreixement impulsiu de l'amplitud de la curvatura reprodueix qualitativament la traça en la velocitat vertical que mostren les dades. En conclusió, aquest treball ens ha permès quantificar les capacitats de Gaia per a caracteritzar la geometria i la dinàmica de la curvatura del disc galàctic.

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La historia de la astronomía es tan antigua como alcanzan nuestros registros. Todas las civilizaciones han estado interesadas en el estudio del cielo nocturno, sus objetos y fenómenos. Estas observaciones se realizaron a simple vista hasta el comienzo del siglo XVII, cuando Galileo Galilei empezó a usar un instrumento desarrollado recientemente llamado telescopio. Desde entonces, el rango de longitudes de onda accesible ha ido creciendo, con una explosión en el siglo XX gracias al desarrollo de instrumentos para observar los diferentes rangos: antenas (radio y submilimétrico), telescopios (óptico e infrarrojo) y satélites (ultravioleta, rayos X y rayos gamma de baja energía). Las últimas longitudes de onda del espectro electromagntico a las que se han accedido han sido los rayos gamma de muy alta energía. En este rango, los flujos son tan bajos que no pueden ser observados por instrumentos espaciales, cuyas áreas de colcción típicas son del orden de O(1) m2. Para detectar esta radiación, usamos la conocida como “imaging atmospheric Cherenkov technique”, basada en la detección de los flashes de luz Cherenkov que los rayos gamma de muy alta energía producen cuando interaccionan con la atmósfera. Este campo es muy joven, con la primera fuente descubierta en 1989 por el pionero telescopio Whipple. Es muy dinámico, con más de 150 fuentes detectadas hasta la fecha, la mayoría de ellas por MAGIC, HESS y VERITAS, que forman la generación actual de estos instrumentos. Finalmente, el campo es también muy prometedor, con la preparación de la siguiente generación de telescopios de este tipo: CTA, una matriz de telescopios que se espera completar en 2020. El trabajo presentado en esta tesis comprende todos los esfuerzos que he realizado para hacer que la astronomía de rayos gammas usando telescopios Cherenkov avance. La Parte I de la tesis es una introducción al universo no térmico, la técnica de “imaging atmospheric Cherenkov” y los IACTs MAGIC and CTA. La Parte II comprende todo el trabajo técnico realizado para conseguir bajar el umbral de energía de los IACTs. Esta parte incluye la simulación, caracterización y test del sistema de trigger analógico dise˜nado para alcanzar el umbral de energía más bajo posible con los LSTs de CTA. Junto a este trabajo, se ha buscado mejorar el sistema de trigger del telescopio MAGIC simulando, testando y poniendo en marcha un nuevo concepto de sistema de trigger estéreo para MAGIC . Este nuevo sistema, que usa la información de la posición de las cascadas en cada una de las cámaras de MAGIC para eliminar ruido, se denomina “Topo-trigger”. La parte científica de la tesis trata de fuentes galácticas observadas con los telescopiosMAGIC En la Parte III hablo del análisis de la emisión de rayos gamma de muy alta energía de pleriones: El descubrimiento de emisión de rayos gamma de muy alta energía del desconcertante plerión 3C 58, probable remanente de la SN 1181 AD y el plerión más débil detectado a estas energías hasta la fecha; la caracterización de la cola de emisión a las más altas energías detectadas desde la nebulosa del Cangrejo observándola a los más altos ángulos zenitales posibles; y el estudio de una componente adicional debido al efecto Compton inverso en los estallidos de rayos gamma reportados por el satélite Fermi-LAT en el régimen de sincrotrón. La Parte IV incluye la búsquedas de rayos gamma de muy alta energía de estrellas variables cataclísmicas. En un contexto multibanda, estudiamos la naturaleza de la emisión de rayos gamma de alta energía previamente declarada de la variable cataclísmica AE Aqr. También realizamos observaciones de novas y una nova enana para desvelar los mecanismos de aceleración que tienen lugar en este tipo de objetos y descubrir una componente hadrónica putativa de la emisión de rayos gamma de baja energía. Un capítulo de conclusiones resume todo el trabajo realizado y los prospectos relacionados con los temas tratados en esta tesis. / The history of astronomy is as ancient as the reach of our written records. All the human civilizations have been interested in the study and interpretation of the night sky and its objects and phenomena. These observations were performed with the naked eye until the beginning of the 17th century, when Galileo Galilei started to use an instrument recently developed called telescope. Since then, the range of accessible wavelengths has been increasing, with a burst in the 20th century with the developing of instruments to observe them: antennas (radio and submillimeter), telescopes (optical, IR) and satellites (UV, X-rays and soft gamma rays). The last wavelength range accessed was the Very-High-Energy (VHE) gamma rays. At this range fluxes are so low that it is not possible to use space-based instruments with typical collection areas of O(1) m2. We must resort to the imaging atmospheric Cherenkov technique, which is based on the detection of the flashes of Cherenkov light that VHE gamma rays produce when they interact with the Earth’s atmosphere. The field is very young, with the first source discovered in 1989 by the pioneering Whipple telescope. It is very dynamic with more than 150 sources detected to date, most of them by MAGIC, HESS and VERITAS, that make up the current generation of instruments. Finally, the field is also very promising, with the preparation of a next generation of imaging atmospheric Cherenkov telescopes: CTA, that is expected to start full operation in 2020. The work presented in this thesis comprises my e orts to take the ground-based -ray astronomy one step forward. Part I of the thesis is an introduction to the nonthermal universe, the imaging atmospheric Cherenkov technique and the Imaging Atmospheric Cherenkov Telescopes (IACTs) MAGIC and CTA. Part II deals with several ways to reduce the trigger threshold of IACTs. This includes the simulation, characterization and test of an analog trigger especially designed to achieve the lowest possible energy threshold with the LSTs of CTA. Together with this work, the trigger of the MAGIC telescopes was improved. We have simulated, tested and commissioned a new concept of stereoscopic trigger. This new system, that uses the information of the position of the showers on each of the MAGIC cameras, is dubbed “Topo-trigger”. The scientific fraction of the thesis deals with galactic sources observed with the MAGIC telescopes. In Part III, I talk about the analysis of the VHE -ray emission of Pulsar Wind Nebulae (PWNe): the discovery of VHE -ray emission from the puzzling PWN 3C 58, the likely remnant of the SN 1181 AD and the weakest PWN detected at VHE to date; the characterization of the VHE tail of the Crab nebula by observing it at the highest zenith angles; and the search for an additional inverse Compton component during the Crab nebula flares reported by Fermi-LAT in the synchrotron regime. Part IV is concerned with searches for VHE -ray emission of cataclysmic variable stars. I studied, on a multiwavelength context, the VHE -ray nature of the previously claimed pulsed -ray emission of the cataclysmic variable AE Aqr. I also performed observations of novae and a dwarf nova to pinpoint the acceleration mechanisms taking place in this kind of objects and to discover a putative hadronic component of the soft -ray emission. A conclusion chapter summarizes all the work performed and lists prospects related with the topics treated in this thesis.

The main purpose of this thesis is to map the radial variation of the stellar density for the young stellar population in the Galactic anticenter direction in order to understand the structure and location of the Perseus spiral arm. A uvbyHbeta Stroemgren photometric survey covering 16 square degrees in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. This is the natural photometric system for identifying young stars and obtaining accurate estimates of individual distances and ages. As a result, a main catalog of 35974 stars with all Stroemgren indexes has been obtained, together with a extended one with 96980 stars with partial data. The central 8 square degrees have a limiting magnitude of V~17mag, while the outer region reaches V~15.5mag. These large samples permit us to analyze the stellar surface density variation associated to the Perseus arm and to study the properties of the stellar component and the interstellar extinction in the anticenter direction. To compute the physical parameters for these stars two different approaches have been used, 1) the available pre-Hipparcos empirical calibrations based on cluster data and trigonometric parallaxes, and 2) a new model based method using atmospheric models and evolutionary tracks, optimized for stars up to Teff>7000K. Results for both of them have been compared with Hipparcos data looking for possible biases and trends. The obtained physical parameters allow us to select the intermediate young stars useful for our studies (B5-A3). These stars are young enough to still have a small intrinsic velocity dispersion (making them respond stronger to a perturbation), but they are also old enough to have approached a dynamic equilibrium with the spiral perturbation. Through their stellar distances, and after defining distance complete samples between 1.2 and 3kpc, we can trace the density distribution in the anticenter direction, finding a clear overdensity around 1.7kpc with an amplitude of 10% that can be associated to the Perseus arm. Those distance complete samples, having a statistical significant number of stars, built using the new model based method for distance estimation, show a significance of the Perseus arm peak overdensity larger than 3sigma. Exponential fittings also allowed us to constrain the radial scale length of the young population of the Galaxy between 2.0 and 2.6kpc, as well as to estimate the stellar density at the solar vicinity for stars between B4 and A1 type stars in 0.022star/pc2, well in agreement with the results obtained in the new version of the Besancon Galaxy Model. In addition, all these data allow the creation of a 3D extinction map, that carefully analyzed shows the presence of a dust layer clearly in front of the location of the stellar overdensity of the arm, suggesting that the corotation radius of the spiral pattern is further away of the position of the Perseus arm. The detection of this dust lane supports the existence of a density wave. Definitive confirmation will come from the ongoing spectroscopic survey using WYFFOS at the William Herschel Telescope in order to obtain radial velocities for a large subsample of the stars in our photometric catalog, that will allow us to trace the possible kinematic perturbation due to the presence of the Perseus arm. / Avui en dia, i després de molts anys d’investigació, encara no disposem d’una teoria completa sobre la forma i l’origen dels patrons espirals de la Via Làctia. I tot i ser conscients que són un factor important per explicar l’evolució dels discos galàctics, la manca d’evidències observacionals sobre els braços espirals de la nostra Galàxia és evident. Moltes preguntes clau encara no tenen resposta, com ara: quin és el mecanisme de formació i evolució de l’estructura espiral en discs estel•lars? Es tracta d’estructures transitòries o són estructures de llarga durada? Quins són els seus components bàsics; estrelles o gas? El treball realitzat durant aquesta tesi pretén ajudar a resoldre algun d’aquests interrogants. El principal objectiu és traçar el braç espiral de Perseu en la direcció de l’anticentre Galàctic. La feina desenvolupada es pot separar en tres apartats. En primer lloc, un mostreig amb fotometria Strömgren en la direcció de l’anticentre Galàctic, mitjançant el qual hem obtingut un catàleg de 96.980 estrelles, 35.974 d’elles amb informació completa en els sis filtres uvbyHβ, i totes elles en una regió de 16 graus quadrats del cel. En segon lloc, per tal d’obtenir els paràmetres físics per a aquestes estrelles, hem creat un nou mètode a partir de models atmosfèrics i evolutius. Finalment, s’ha utilitzat tota aquesta informació per estudiar la distribució de la densitat estel•lar en la direcció de l’anticentre. Aquestes dades també ens han permès crear un mapa d’extinció tridimensional, a partir del quan hem analitzat la distribució de pols així com la seva relació amb el braç espiral de Perseu.

Since white dwarfs are the final stage of the evolution of the vast majority of stars, they carry important information about the chemical evolution of our Galaxy, its star formation rate, and its structure and dynamics. This thesis pays attention to two related but distinct astrophysical problems involving white dwarfs. The first of these problems concern the nature and the location of the microlensing events towards the Large Magellanic Clouds (LMC), which still remains a mystery. The main observational groups, MACHO and EROS, are in dispute each, yet agreement has now been reached in some of the most important points. The second of the problems we address in this thesis is an open problem as well. Close compact binaries are at the heart of several interesting phenomena in our Galaxy as well. Close compact binaries are formed through at least one common envelope episode. Even though the basics concepts of the evolution during a common envelope phase are rather simple, the details are still far from being well understood. To shed light on these problems, we used an existing Monte Carlo simulator. We expanded this simulator integrating the most up-to-date white dwarfs cooling models as well as detailed modeling of our Galaxy and the LMC in order to mimic both the MACHO and EROS experiments. Additionally, we included the red dwarf population and performed a joint analysis of the contributions of both populations to the dark matter content of our Galaxy. Moreover, we studied the contribution of the subpopulation of white dwarfs with hydrogen-deficient atmospheres. On the other hand, our Monte Carlo code has been expanded to deal with those systems composed by a white dwarf and a main sequence star, which have evolved through a common episode. A detailed implementation of several different physical processes, including a full description of the mass transfer episode, a complete treatment of the Roche lobe overflow episode, gravitational tides and orbital evolution of the binary system, was performed. Furthermore, in our treatment we carefully included all the different selection criteria and observational biases. This allowed us to make a meaningful comparison with the available data, besides examining the role played by the binding energy parameter and by the common envelope parameter, not to mention the role played by the distribution of secondary masses of the binary systems. The results of our Monte Carlo simulations of the microlensing experiments show agreement with the findings of the EROS and MACHO survey. Our findings show that neither white dwarfs nor red dwarfs can be major contributors to the microlensing depth towards the LMC. These facts reinforce the idea, previously pointed by others studies, that the optical depth found by the MACHO survey is highly likely an overestimate, probably due to contamination of self-lensing objects, amid other possible explanations. Concerning the second point of this thesis, our Monte Carlo simulations correctly reproduce the properties of the observed population of post-common envelope white dwarf plus main sequence binaries, once biases are taken into account. The best-fit models are obtained with fractions less than ~20% of the internal energy contributing to the ejection of the star progenitor¿s envelope, and values for the common-envelope efficiency parameter less than ~0.3. To conclude, the work presented in this thesis poses an important step forward not only in constraining the microlensing discoveries, but also in validating models for the observed white-dwarf populations of our Galaxy.

The purpose of this work has been the study of Radio Emitting X-Ray Binaries (REXRBs) both from the observational and theoretical approaches. We have mainly concentrated in the analysis of their properties inferred from their emission in radio and X-ray wavelengths. Our observational contribution has been done specially at different centimetric and millimetric wavelengths, although contrast with other bands of the electromagnetic spectrum has been always considered. From the about 25 REXRBs detected, we have directly observed and analyzed the sources LS 1+61 °303 and Cygnus X-3, both radiostars known for they highly variable radio emission events. The most remarkable characteristic of LS I+61°303 is the recurrent display of radio outbursts that show complex light curve profiles with a period similar to 26.5 days. It is noticeable that, with the exception of pulsars, LS I+61°303 and Cygnus X-l, are the only two known periodic radio sources. Cygnus X-3 is also well known for the exhibition of strong radio flares. The system spends most of the time in quiescent state, at a level of few hundreds of mJv. It normally exhibits variability in time scales of hours suspected of having periodical or quasi periodical trends. When an outburst occurs the source reaches peak flux densities of tens of Jv at centimetric wavelengths, which converts it during some days in one of the brightest radio source of the sky. Cygnus X-3 strong flares are irregularly spaced with a mean recurrence interval of ~120 days. The flaring events are believed to involve the ejection and acceleration of ionized plasma clouds (plasmons) responsible for the radio emission via synchrotron radiation. The reasons for selecting this two sources as the objects to use in our study are mainly related to their flaring behaviour, and they can be summarized in the following points: · Due to their outbursting properties they are intrinsically interesting as independent sources among the REXRBs. · The sudden release of relativistic particles that provokes the flaring radio emission can help to better understand the origin of such particles and conditions of the system at the epochs of the outburst occurrence. That can be extrapolated to non-flaring radio emitters. · In concrete, the periodical behaviour of LS I+61°303 (the only REXRB of such characteristic in the northern hemisphere) allows to predict the phases when the source is in active state. Such predictability facilitates the scheduling of observations, depending on whether we are interested to perform the experiment in quiescence or in active state. It also permits to coordinate different instruments for multiple energy band monitoring of the source, normally preferred when it is in a high emission state. · The periodical behaviour itself is also very interesting. It is presumably related to the orbital motion of the system, and onset of outburst are suspected to occur near the periastron passage. Such behaviour can indicate a very eccentric orbit for the binary system LS I+61°303. The confirmation of such issues can provide clues for physical parameters also for more steady radio emitting REXRBs. as well as for non radio emitting X-ray binaries. · The observation of the temporal and spectral evolution of a radio flaring event, as well as the source structure at different spatial scales during it, can provide us with useful information of the mass of the particles involved, the energetic evolution of such radiating particles, the velocities acquired by the possible radio emitting bulk and its expansion rates, and the scenario in which the source is embebbed (geometry and strength of the magnetic field, surrounding non relativistic material, etc). · And finally, the study of these two objects is a continuation of the work per-formed by members of the research group where the author is integrated. They disposed of previous observations of these objects, as well as experience in radio single dish, and array observations and wide knowledge of this REXRBs and the different physical models that could describe them. This report is structured in 11 chapters, being the bulk of them (with the exception of the present one) distributed in three main differentiated parts. Each part is a compilation of the work performed to study the next different aspects of REXRBs and in particular of our selected objects: Part I - Highly energetic processes in REXRBs emission: In Chapter 2 we develop a theoretical model of the radio and X-ray emission arisen from a plasmon of relativistic particles within a REXRB scenario. In Chapter 3 we apply this model to observations of LS I+61°303 and Cygnus X-3. Part II - Radio images: We analyze sub-arsecond, arcsecond and arcminute images we have performed from different observation campaigns of LS I+61°303 and Cygnus X-3. They are described in Chapters 4, 5 and 6. Part III - Search for periodic behaviour in the radio and X-ray light curves: After a brief description of statistical methods to look for a periodic signal from a data set, in Chapter 7 we apply them to analyze the long and short time scales of the variable behaviour of the target sources. Chapter 8 is devoted to look for the instabilities in the ~ 26.5 days radio period of LS I+61°303, and Chapter 9 to analyze its 'micro-flares' repetitive behaviour at certain phases. Chapter 10 is as well devoted to periodicities of LS I+61°303, but in this case in the X-ray domain, and, finally, Chapter 11 analyzes the hour scale fluctuations observed in Cygnus X-3. / TÍTOL DE LA TESI:"Les estrelles binàries de raigs X amb emissió ràdio LS I+61°303 i Cygnus X-3" TEXT: Les binàries o estrelles dobles físiques són sistemes formats per dues estrelles lligades gravitatòriament. Avui en dia sabem que aquest és un fenomen molt comú a la Galàxia, on aproximadament la meitat de les estrelles s'han format donant lloc a aquesta mena de sistemes. Històricament, el seu estudi ha proporcionat molta informació sobre la física estel·lar. Per exemple, fins no fa gaire els sistemes binaris eren la millor eina disponible per a la mesura directa de la massa dels estels. Ha estat també gràcies a observacions de sistemes binaris contenint púlsars que s'ha obtingut la verficació de previsions de la teoria de la Relativitat General. Durant gran part de la seva vida, les components d'un sistema binari orbiten a distancias comparativament més grans que les dimensions del volum on domina la influència gravitatòria de cadascuna de les components (lòbul de Roche). Durant aquest temps, les estrelles del sistema evolucionen de la mateixa manera que ho farien si es trobessin aïllades. No obstant, les diferents etapes de l'evolució estel·lar per les que, inexorablement, cadascuna de les components haurà de passar segons la seva massa, poden fer que els paràmetres físics del sistema (massa, radi, semieix de l'òrbita, vent estel·lar, etc.) varîin apreciablement. A conseqüència d'aquests canvis, es poden produir situacions en què el radi d'una de les components es faci comparable, o fins i tot l'excedeixi, al tamany característic del seu lòbul de Roche. A partir d'aquí, és possible que s'estableixi una tranferència de massa entre les components del sistema. Altrament, aquesta transferència també poder ésser deguda al vent estel·lar. La captura o acreció d'una fracció d'aquesta massa, perduda pel-la component "donant", per part de la seva companya pot donar lloc a fenòmens capaços de modificar apreciablement les propietats globals del sistema, a l'hora que també pot generar un ampli ventall de fenòmens observacionals que es manifesten en gairebé tot l'espectre electromagnètic. És molt variada la "fauna" de sistemes binaris interactuants segons sigui el mecanisme concret de transferència de massa i el tipus d'estrelles components. En aquest treball ens ocupem en particular de les anomenades binàries de raigs X, de les quals s'en coneixen actualment més d'un centenar. Entre elles, però, centrem la nostra atenció en les que, a més, han estat detectades en ones de ràdio, a les quals ens referirem simplement per brevetat com a ràdio binàries X. Aquesta subclasse de les binàries de raigs X, amb emissió ràdio associada, és certament força heterogènia i fins avui s'en coneixen de l'ordre de 20 casos. A títol d'exemple, aquests inclouen sistemes com Cygnus X-l, el primer canditat a forat negre, LS I+61°303 i Circinus X-l, les dues úniques ràdiofonts del cel clarament periòdiques a part dels pulsáis, i Cygnus X-3, famosa per les seves erupcions ràdio on la lluminositat augmenta fins a tres ordres de magnitud en poc més d'un dia. L'interés astrofísic d'aquestes ràdio binàries X es podia entendre, fins no fa gaire, només en que molts dels processos físics que hi tenen lloc són versions a escala reduïda del que succeix en algunes galàxies actives i quàsars. Això ja és de per sí remarcable doncs, donat que totes elles són objectes pertanyents a la nostra Galàxia i per tant relativament propers, les tècniques observacionals de la Interferometria de Base Molt Llarga ( Very Long Base-line Interferometry o VLBI) ens permeten assolir-hi unes ressolucions espaials (~ 1 AU) impensables en una font extragalàctica. D'altra banda, les escales temporals d'emissió en ràdio binàries són relativament curtes (mesos o dies) i, en ocasions, fins i tot periòdiques d'acord amb el període orbital del sistema. Això facilita enormement preveure les èpoques d'observació en que hom espera més activitat. D'altra banda, aquest tipus d'objectes s'han beneficiat considerablement dels darrers avenços en les tècniques observacionals, tant des de terra com des de l'espai, que actualment fan possible realitzar observacions astronòmiques en tots els dominis de l'espectre electromagnètic. Això és particularment interessant quan s'aplica a astres que siguin détectables a la vegada en més d'un aquests dominis, com és el cas de les ràdio binàries X. Aleshores, les observacions multi-espectrals representen una eina molt important per a contrastar l'elaboració de models teòrics capaços de reproduir, de manera unificada, el comportament observat a longituds d'ona molt diferents (ràdio, infrarroig, òptic, ultraviolat, raigs X i raigs Gamma). Més recentment, però, s'hi ha afegit un nou punt d'interés després del descobri-ment de diverses fonts de raigs X durs (> 40 keV) en la direcció del centre galàctic. Aquests nous objectes presenten una contrapartida ràdio constituïda per una font central compacta i variable de la qual emana un jet bipolar. La interpretació més probable és que es tracta de ràdio binàries X on la component compacta és un forat negre amb un disc d'acreció, perpendicularment al qual s'ejecta plasma altament relativista en forma de jet col.limat. Una d'elles, GRS1915+105, ha resultat ser la primera ràdiofont coneguda de la Galàxia que ejecta matèria a velocitats aparent-ment superlumíniques. En general, les binàries de raigs X són sistemes formats per un estel normal i un objecte compacte i col·lapsat. Aquest darrer és habitualment un estel de neutrons però, en ocasions, pot tractar-se d'un forat negre. El nom de binàries de raigs X es justifica pels processos d'acreció de matèria sobre l'objecte compacte, els quals originen intenses emissions en aquest domini espectral. Segons la massa de l'estel normal, que actua com a donant de matèria, les binàries de raigs X es classifiquen a grans trets en d'alta massa o de baixa massa, sense que es coneguin exemples intermitjos. La component normal de les binàries massives pertany típicament a tipus espectrals primerencs mentre que, en les poc massives, aquesta és de tipus espectral més tardà. Suposem que la component compacta del sistema binari acreta matèria a un cert ritme Macc- Aleshores, la lluminositat del sistema Lacc es pot estimar suposant que tota l'energia cinètica del material acretat s'allibera en forma de radiació.

Se puede dividir mi tesis en tres partes: 1. Estudios de la emisi.n gamma de los sistemas binarios LS I +61 303 y LS 5039 a altas energ.as con el Fermi Large Area Telescope (LAT) y el primer descubrimiento de variabilidad superorbital a altas energ.as de la fuente LS I +61 303 Los sistemas binarios de rayos gamma son sistemas estelares cuyo espectro tiene su máximo a altas energías (sin tener en cuenta su emisión térmica). Ha sido detectada desde radio hasta rayos gamma (TeV), el sistema binario LS I +61 303 es muy variable en todas las frecuencias. Una característica de la variabilidad de este sistema es la modulación de su emisión a 26.496 días que coincide con su período orbital. En esta tesis mostramos por primera vez que la emisión gamma de LS I +61 303 presenta también una variabilidad superorbital con un período de 1667 días. Esta modulación es más presente en fases orbitales alrededor de apastro, aunque no introduce un cambio visible cerca de periastro. Además, se observa una aparición y desaparición de la variabilidad orbital en el espectro de potencias de los datos. Este comportamiento se puede explicar por una evolución cuasi-°©‐cíclica del disco ecuatorial de la estrella acompañante (estrella Be) cuyas características influyen en las condiciones para generar rayos gamma. Estos descubrimientos abren por primera vez la posibilidad de usar observaciones de rayos gamma para estudiar los discos de estrellas masivas en sistemas binarios excéntricos. 2. Estudios de la emisi.n gamma de magnetares a altas y muy altas energ.as con el LAT y con los telescopios Cherenkov MAGIC Los magnetares son una clase particular de estrellas de neutrones que muestran emisión desde radio hasta unos centenares de keV. Se pueden caracterizar por sus explosiones de rayos X y por sus perdidas de energía, las cuales son demasiado pequeñas para justificar su luminosidad en rayos X. Por esta razón, la teoría más aceptada es que la emisión X de la estrella de neutrones está suministrada por el decaimiento y las inestabilidades de sus altos campos magnéticos. En esta tesis, estos objetos han sido estudiados por primera vez a altas y a muy altas energías con el LAT y con los telescopios MAGIC. Hemos impuesto las primeras cotas a la posible emisión gamma de estos objetos. Además, este fuerte diagnóstico observacional fuerza una revisión del espacio de parámetros aplicable a la visibilidad del modelo de “outer gap” de Cheng & Zhang (2001) and Zhang & Cheng (2002) para cada magnetar. 3. Predicciones para la astronom.a Cherenkov con los telescopios CTA La siguiente generación de telescopios Cherenkov será CTA. Este experimento está ahora en la fase de diseño. En esta tesis, evaluamos las capacidades de CTA para estudiar la física no-°©‐térmica de sistemas binarios de rayos gamma. Eso requiere la observación de fenómenos a altas energías a tiempos y a escalas espaciales diferentes. Para hacer eso, hemos estudiado los sistemas binarios de rayos gamma en el contexto de la física conocida o esperada de estas fuentes. CTA será capaz de demostrar los procesos físicos detrás de la emisión gamma en sistemas binarios con una resolución espectral, temporal y espacial alta. Además crecerá el número de fuentes detectadas significativamente. Hemos observado que la sensibilidad de CTA conseguirá un muestreo de curvas de luz y espectros a escalas de tiempo muy cortas de alta calidad. Además, se podrá monitorear fuentes a tiempo largo usando una parte de los telescopios que todavía alcanzará una sensibilidad 2 o 3 veces mayor que cualquier instrumento actual operando a muy altas energías. En particular, es notable que CTA reducirá la indeterminación de los flujos e índices espectrales en unos cuantos factores. / My thesis can be divided into three parts: 1. Study of the gamma-­ray emission of the binary systems LS I +61 303 and LS 5039 at high energies with the Fermi Large Area Telescope (LAT) and the first discovery of superorbital variability at high energies from the source LS I +61 303. Gamma-­‐ray binaries are stellar systems for which the spectral energy distribution (discounting the thermal stellar emission) peaks at high energies. Detected from radio to TeV gamma rays, the gamma-­‐ray binary LS I +61 303 is highly variable across all frequencies. One aspect of this system's variability is the modulation of its emission with the timescale set by the 26.496-­‐day orbital period. In this thesis we show for the first time that the gamma-­‐ray emission of LS I +61 303 also presents a sinusoidal variability at the known superorbital period of 1667 days. This modulation is more prominently seen at orbital phases around apastron, whereas it does not introduce a visible change close to periastron. It is also found in the appearance and disappearance of variability at the orbital period in the power spectrum of the data. This behavior could be explained by a quasi-­‐cyclical evolution of the equatorial outflow of the Be companion star, whose features influence the conditions for generating gamma rays. These findings open for the first time the possibility to use gamma-­‐ray observations to study the outflows of massive stars in eccentric binary systems. 2. Study of the gamma-­ray emission of magnetars at high and very high energies with the LAT and the MAGIC Cherenkov telescopes. Magnetars are a peculiar class of neutron stars showing emission from radio up to some hundreds of keV. They can be characterized through their bursting behavior and through an energy loss rate, which is too small to power their X-­‐ray luminosity. Therefore, it is believed that the X-­‐ray emission of the neutron star is powered by the decay and the instabilities of their strong magnetic field. In this thesis, these objects are studied for the first time at high and very high energies with the LAT and the MAGIC telescopes. We put the first constraints on their emission in this high energy regime. Furthermore, this strong observational diagnostic forces a revision of the parameter space applicable for the viability of the outer gap model of Cheng & Zhang (2001) and Zhang & Cheng (2002) to each magnetar. 3. Prospects for the Cherenkov astronomy with the future Cherenkov Telescope Array (CTA). The next generation of Imaging Air Cherenkov Telescopes will be CTA. This experiment is nowadays in the design phase. In this thesis we evaluate the potentialities of CTA to study the non-­‐thermal physics of gamma-­‐ray binaries, which requires the observation of high-­‐energy phenomena at different time and spatial scales. To do so we study gamma-­‐ray binaries in the context of the known or expected physics of these sources. CTA will be able to probe with high spectral, temporal and spatial resolution the physical processes behind the gamma-­‐ray emission in binaries, significantly increasing as well the number of known sources. We found that the sensitivity of CTA will lead to a very good sampling of light curves and spectra on very short timescales. It will allow as well long source monitoring using subarrays, still with a sensitivity 2–3 times better than any previous instrument operating at VHE energies. In particular, it is noteworthy that CTA will reduce by a factor of a few the errors in the determination of fluxes and spectral indexes.