Nos encontramos em uma localização vantajosa para o estudo da formação e evolução de galáxias espirais. Situados no disco da Via-Láctea, somos capazes de fazer observações detalhadas sobre as estrelas individuais que a compõem. Com o avanço tecnológico das últimas décadas, foi possível coletar um grande conjunto de informações, (e.g. composição química, cinemática, astrometria e parâmetros atmosféricos), com alta resolução para uma vasta parte do volume Galáctico. Com o objetivo de compreender melhor a nossa Galáxia, desenvolvemos uma ferramenta, chamada StarHorse, que estima parâmetros como distâncias, idades, massas e avermelhamento utilizando informação disponível em levantamentos espectroscópicos, fotométricos e astrométricos. O código StarHorse estima os parâmetros através de um método Bayesiano, que constrói uma distribuição de probabilidade a partir do cálculo de verossimilhança entre observações e modelos de evolução teórica e a partir de priores Galácticos bem conhecidos. Os parâmetros que o StarHorse estima são cruciais para estudos de arqueologia Galáctica. Com eles é possível investigar a estrutura, o histórico de formação estelar, a função de massa inicial, o mapa tridimensional da nossa Galáxia e também adicionar vínculos a modelos quemodinâmicos da Via Láctea Neste trabalho, focaremos na descrição e validação do método, testando sua aplicabilidade em levantamentos recentes de espectroscópica, astrometria e fotometria. Também disponibilizamos catálogos com distâncias e extinção para comunidade astronômica. As nossas distâncias e extinções se tornaram referência dentro da colaboração APOGEE e foram liberadas junto com o seu Data Release 14. Ademais, catálogos foram liberados para os surveys RAVE, Gaia-ESO e GALAH. Neste trabalho, exploramos os resultados do StarHorse, especialmente os resultados APOGEE, em um contexto amplo de arqueologia Galáctica. / We are in an advantageous position to study the formation and evolution of disk galaxies. By being inside the Milky Way, we are able to make detailed observations about the individual stars that compose it. With the technological revolution of the latest years, it has been possible to collect a massive set of information, (e.g. chemical composition, kinematics, astrometry, and atmospheric parameters), with high resolution for a large portion of the Galactic volume. With the goal to understand better our Galaxy, we developed a tool, called StarHorse, that can estimate distances, ages, masses, and extinction from the available spectroscopic, astrometric, and photometric information. StarHorse makes these estimates through a Bayesian method, that builds a probability distribution over the models by calculating a likelihood function between observation and stellar evolution models, and by using common knowledge about our Galaxy as priors. The parameters that StarHorse estimates are crucial to Galactic archaeology studies. With them, we can investigate the structure, the star formation history, the initial mass function, the three-dimensional dust map of our Galaxy, and provide constraints to chemodynamical models of the Milky Way. In this work, we focus on the description and validation of the method, testing its applicability in recent spectroscopic and astrometric surveys. We also make available catalogs with distances and extinctions to the astronomy community. Our distances and extinctions became a reference inside the APOGEE-team and were released as part of the SDSS Data Release 14. Moreover, we made available catalogs also to other spectroscopic surveys such as Gaia-ESO, RAVE, and GALAH. In this work, we also explore these results, especially for APOGEE, in a broad Galactic archaeology context.

M dwarf stars make up over 70% of stars by number in the Milky Way Galaxy and are known to host at least two exoplanets per star on average. Using mutually eclipsing double-lined spectroscopic binary stars (SB2 EBs), astronomers can empirically measure stellar properties of M dwarf stars including mass and radius. However, empirical measurements systematically differ from the predictions of stellar evolutionary models and show large scatter. Some M dwarf stars are outliers, with radii that are a factor of 2-to-3 larger than model predictions, assuming they were measured accurately. In this dissertation, I investigated whether the outliers, systematic offset, and the scatter seen in the mass-radius diagram are physical, using SB2 EBs with photometry from NASA's Kepler Mission and high-resolution near-infrared ground-based spectroscopy. Empirical measurements using space-based photometry and high-resolution near-infrared ground-based spectroscopy, together with Bayesian model-fitting techniques, provide significant advancements over previous measurements. For this dissertation work, a sample of Kepler EBs were carefully chosen to be detached and non-interacting. I conducted a radial velocity survey of the sample using Immersion GRating INfrared Spectrometer (IGRINS) with the Discovery Channel Telescope (DCT) and iSHELL with NASA's Infrared Telescope Facility (IRTF). Combined with high-precision Kepler data, I determined the masses and radii of the component stars in the sample. I also determined a new mass-radius relationship of M dwarf stars using the sample of Kepler EB systems. My investigation showed that the outliers in the mass-radius diagram of M dwarf stars are not physical and they are due to the quality of data and from analysis using different pipelines. I also showed that the offset and scatter in the mass-radius diagram are persistent, which are not from the measurement uncertainties. This suggests the need for an extra degree of freedom to accurately capture the discrepancies between the empirical measurements and model predictions. Lastly, I showed that reduced convective heat flow due to enhanced magnetic fields from rapid stellar rotation can account for the offset and scatter in the measurements.

Two red supergiants (RSGs) of the Per OB1 association, RS Per and T Per, have been observed in the H band using the Michigan Infra-Red Combiner (MIRC) instrument at the CHARA array. The data show clear evidence of a departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. The stellar surfaces are first modeled as limb-darkened disks based on SATLAS models that fit both MIRC interferometric data and publicly available spectrophotometric data. Bayesian model selection is then used to determine the most probable number of spots. The effective surface temperatures are also determined and give further support to the recently derived hotter temperature scales of RSGs. The stellar surfaces are reconstructed by our model-independent imaging code SQUEEZE, making use of its novel regularizer based on Compressed Sensing theory. We find excellent agreement between the model-selection results and the reconstructions. Our results provide evidence for the presence of near-infrared spots representing about 3%-5% of the stellar flux.

We have identified 1027 star-forming complexes in a sample of 46 galaxies from the Spirals, Bridges, and Tails (SB&T) sample of interacting galaxies, and 693 star-forming complexes in a sample of 38 non-interacting spiral (NIS) galaxies in 8 μm observations from the Spitzer Infrared Array Camera. We have used archival multi-wavelength UV-to IR observations to fit the observed spectral energy distribution of our clumps with the Code Investigating GALaxy Emission using a double exponentially declined star formation history. We derive the star formation rates (SFRs), stellar masses, ages and fractions of the most recent burst, dust attenuation, and fractional emission due to an active galactic nucleus for these clumps. The resolved star formation main sequence holds on 2.5 kpc scales, although it does not hold on 1 kpc scales. We analyzed the relation between SFR, stellar mass, and age of the recent burst in the SB&T and NIS samples, and we found that the SFR per stellar mass is higher in the SB&T galaxies, and the clumps are younger in the galaxy pairs. We analyzed the SFR radial profile and found that the SFR is enhanced through the disk and in the tidal features relative to normal spirals.

Comprehensive and robust analysis of galaxies found throughout cosmic time provides the means to probe the underlying characteristics of our Universe. Coupling observations and theory, spectral energy distribution (SED) fitting provides a method to derive the intrinsic properties of distant galaxies which then aid in defining galaxy populations and constraining current galaxy formation and evolution scenarios. One such population are the sub-millimeter galaxies (SMGs) whose high infrared luminosities -- typically associated with dust-obscured star formation -- and redshift distribution places them as likely key components in galaxy evolution. To fully analyze these systems, however, requires a near complete sampling of the full SED, detailed models that encapsulate the variety of physical processes and sophisticated methods for comparing the data and models. In this dissertation, we present the general propose, Monte Carlo Markov Chain (MCMC) based SED fitting routine SED Analysis Through Markov Chains (SATMC) and the insight we have gained in modeling a sample of AzTEC 1.1mm-detected SMGs. The MCMC engine and Bayesian formalism used in the construction of SATMC offers a unique view at the constraints on model parameter space that are often grossly simplified in traditional SED fitting methods. We first present the motivation behind SATMC and its MCMC algorithm. We also highlight a series of test cases that verify not only its reliability but its versatility to various astrophysical applications, including the field of photometric redshift estimation. We then present the AzTEC SMG sample and preliminary results obtained through counterpart identification, X-ray spectral modeling and SED fitting with SATMC. Finally, we present the latest work in detailed SED analysis of SMGs and how these results influence our understanding of the SMG population.

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Context. For over 12 yr, we have carried out a precise radial velocity (RV) survey of a sample of 373 G- and K-giant stars using the Hamilton Echelle Spectrograph at the Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries. Aims. We aim at detecting and characterizing substellar and stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616). Methods. We obtained high-precision RV measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. To distinguish between RV variations that are due to non-radial pulsation or stellar spots, we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to characterize the system in more detail, we obtained high-resolution images with LMIRCam at the Large Binocular Telescope. Results. We report the probable discovery of a giant planet with a mass of m(p) sin i = 6.92(-0.24)(+0.18) M-Jup orbiting at a(p) = 1.0860(-0.0007)(+0.0006) aufrom the giant star HD 59686 A. In addition to the planetary signal, we discovered an eccentric (e(B) = 0.729(-0.003)(+0.004)) binary companionwith a mass of m(B) sin i = 0.5296(-0.0008)(+0.0011) M-circle dot orbiting at a close separation from the giant primary with a semi-major axis of a(B) = 13.56(-0.14)(+0.18) au. Conclusions. The existence of the planet HD 59686 Ab in a tight eccentric binary system severely challenges standard giant planet formation theories and requires substantial improvements to such theories in tight binaries. Otherwise, alternative planet formation scenarios such as second-generation planets or dynamical interactions in an early phase of the system's lifetime need to be seriously considered to better understand the origin of this enigmatic planet.

Accurate knowledge of stellar parameters such as mass, radius, effective temperature, and composition inform our understanding of stellar evolution and constrain theoretical models. Binaries and, in particular, eclipsing binaries make it possible to measure directly these parameters without reliance on models or scaling relations. In this dissertation we derive fundamental parameters of stars in close binary systems with and without (detected) tertiary companions to test and inform theories of stellar and binary evolution. A subsample of 41 detached and semi-detached short-period eclipsing binaries observed by NASA’s Kepler mission and analyzed for eclipse timing variations form the basis of our sample. Radial velocities and spectroscopic orbits for these systems are derived from moderate resolution optical spectra and used to determine individual masses for 34 double-lined spectroscopic binaries, five of which have detected tertiaries. The resulting mass ratio M2/M1 distribution is bimodal, dominated by binaries with like-mass pairs and semi-detached classical Algol systems that have undergone mass transfer. A more detailed analysis of KIC 5738698, a detached binary consisting of two F-type main sequence stars with an orbital period of 4.8 days, uses the derived radial velocities to reconstruct the primary and secondary component spectra via Doppler tomography and derive atmospheric parameters for both stars. These parameters are then combined with Kepler photometry to obtain accurate masses and radii through light curve and radial velocity fitting with the binary modeling software ELC. A similar analysis is performed for KOI-81, a rapidly-rotating B-type star orbited by a low-mass white dwarf, using UV spectroscopy to identify the hot companion and determine masses and temperatures of both components. Well defined stellar parameters for KOI-81 and the other close binary systems examined in this dissertation enable detailed analyses of the physical attributes of systems in different evolutionary stages, providing important constraints for the formation and evolution of close binary systems.

Context. Radial velocity and transit methods are effective for the study of short orbital period exoplanets but they hardly probe objects at large separations for which direct imaging can be used. Aims. We carried out the international deep planet survey of 292 young nearby stars to search for giant exoplanets and determine their frequency. Methods. We developed a pipeline for a uniform processing of all the data that we have recorded with NIRC2/Keck II, NIRI/Gemini North, NICI/Gemini South, and NACO/VLT for 14 yr. The pipeline first applies cosmetic corrections and then reduces the speckle intensity to enhance the contrast in the images. Results. The main result of the international deep planet survey is the discovery of the HR8799 exoplanets. We also detected 59 visual multiple systems including 16 new binary stars and 2 new triple stellar systems, as well as 2279 point-like sources. We used Monte Carlo simulations and the Bayesian theorem to determine that 1.05(-0.70)(+2.80)% of stars harbor at least one giant planet between 0.5 and 14 MJ and between 20 and 300AU. This result is obtained assuming uniform distributions of planet masses and semi-major axes. If we consider power law distributions as measured for close-in planets instead, the derived frequency is 2.30(-1.55)(+5.95)%, recalling the strong impact of assumptions on Monte Carlo output distributions. We also find no evidence that the derived frequency depends on the mass of the hosting star, whereas it does for close-in planets. Conclusions. The international deep planet survey provides a database of confirmed background sources that may be useful for other exoplanet direct imaging surveys. It also puts new constraints on the number of stars with at least one giant planet reducing by a factor of two the frequencies derived by almost all previous works.