Dissertations / Theses on the topic 'Observational astronomy'
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Widicus, Weaver Susanna Leigh Beauchamp Jesse L. "Rotational spectroscopy and observational astronomy of prebiotic molecules /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05162005-153745.
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Corrigan, Ruth T. "Observational manifestations of gravitational lenses." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260611.
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Añez, López José Ignacio. "Observational and theoretical perspective of massive star formation." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/671784.
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In this thesis, we are aimed to better understand the massive star formation process paying special attention to the role of the magnetic field. To do this, we will carry out a multi-scale analysis with a double approach, theoretical and observational.
a) The role of the magnetic field in the fragmentation process: the case of G14.225-0.506
In this first work, we study the fragmentation of an infrared dark cloud that has a filamentary structure and two hubs. We will pay special attention to the magnetic field present in the environment of the hubs and we will try to relate it to the different levels of fragmentation that these hubs present.
In order to carry out this study, we present the result of the CSO observations at 350 um, towards both hubs, North and South, in the infrared dark cloud G14.225-0.506 (from here G14.2). We also show the analysis of polarization and intensity gradient making use of the method developed by Koch et al. 2012, Koch et al. 2012b.
In the N-hub we find a magnetic field with a uniform distribution along the east-west direction.
However, in the southern hub the B-field shows a bimodal distribution. The intensity-gradient in the N-hub shows a single local minimum. In the S-hub, the intensity gradient reveals two minima reflecting the bimodal distribution of the magnetic field where each component points to each of the minima of the intensity gradient.
Analysis of the maps |delta| and Sigma_B in the N-hub indicates that, in the vicinity of the hub, gravity dominates the magnetic field. We have also estimated the intensity of the magnetic field finding higher values in the N-hub than in the S-hub. This supports the idea that the different levels of fragmentation exhibited by hubs depend on differences in magnetic field.
b) Modeling the accretion disk around the high-mass protostar GGD 27-MM1
In this second project, we descend to accretion disk scales to understand how massive stars form and evolve. In this work we have used ALMA observations at a wavelength of 1.14~mm with very high angular resolution that resolve the disk around the massive star GGD27-MM1.
Motivated by the similarity of this system to those found in low mass, we have modeled the emission of the disk using the models developed by D'Alessio et al. 2006 for low mass stars. The main objective is to investigate whether the assumptions that are valid for disks around low-mass stars could be extrapolated to the case of massive stars.
As a result we have found a very massive disk of about ~5 Msun which represents around 25 % of the stellar mass. This mass is consistent with the calculated dynamic mass. The disk has a radius of ~170 au with a 49º of inclination. We have compared the temperature and density structure obtained with our model with potential functions and show that the GGD~27--MM1 system is a potential template for future similar studies in other high-mass protostars.
Specifically, we have found a flared disk with a maximum scale height of ~13 au and a temperature profile that goes from ~150 K on the outside of the disk to ~ 1400 K on the inner edge of the disk.
Analysis of the Toomre parameter Q evaluated at the midplane temperature of the disk indicates that the disk is stable up to a radius 100 au.
This work shows that D'Alessio's models can be used as a first approximation and also obtain various observational predictions.En esta tesis, pretendemos contribuir a explicar el proceso de formación de estrellas masivas prestando especial atención al papel del campo magnético. Para ello, realizaremos un análisis multiescala con una doble aproximación, teórica y observacional. Por un lado investigaremos el proceso de acrecimiento a través de un disco de acrecimiento entorno a una estrella de alta masa. a) El papel del campo magnético en el proceso de fragmentación: el caso de G14.225-0.506 En este primer trabajo, estudiamos la fragmentación de una nube oscura infrarroja que presenta una estructura filamentaria y dos hubs. Prestaremos especial atención al campo magnético presente en el entorno de los hubs y trataremos de relacionarlo con los distintos niveles de fragmentación que presentan estos hubs. Para poder llevar a cabo este estudio presentamos el resultado de las observaciones del CSO a 350 masas solares, hacia ambos hubs, Norte y Sur, en la nube oscura infrarroja G14.225-0.506 (desde aquí G14.2). También mostramos el análisis de la polarización y gradiente de intensidad haciendo uso del método desarrollado por (Koch et al. 2012, Koch et al. 2012b). b) El modelado del disco de acrecimiento entorno a la protoestrella masiva GGD 27-MM1 En este segundo proyecto, descendemos hasta escalas de discos de acrecimiento para entender como las estrellas masivas se forman y evolucionan. En este trabajo hemos usado observaciones de ALMA a una longitud de onda de 1.14 mm con muy alta resolución angular (aproximadamente 40 mili-segundos de arco) que resuelven el disco entorno a la estrella masiva GGD27-MM1. El disco se dispone perpendicularmente al espectacular chorro de 10 pc de longitud que emana de la fuente, conocido como HH80-81. Motivados por el parecido de este sistema a los que encontramos en baja masa, hemos modelado la emisión del disco haciendo uso de los modelos desarrollados por D'Alessio et al. 2006 para estrellas de baja masa.
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Kelly, Brandon Charles. "Observational Constraints on the Structure and Evolution of Quasars." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/193633.
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I use X-ray and optical data to investigate the structure of quasars, and its dependence on luminosity, redshift, black hole mass, and Eddington ratio. In order to facilitate my work, I develop new statistical methods of accounting for measurement error, non-detections, and survey selection functions. The main results of this thesis follow. (1) The statistical uncertainty in the broad line mass estimates can lead to significant artificial broadening of the observed distribution of black hole mass. (2) The z = 0.2 broad line quasar black hole mass function falls off approximately as a power law with slope ~ 2 for M_{BH} > 10^8 M_{Sun}. (3) Radio-quiet quasars become more X-ray quiet as their optical/UV luminosity, black hole mass, or Eddington ratio increase, and more X-ray loud at higher redshift. These correlations imply that quasars emit a larger fraction of their bolometric luminosity through the accretion disk component, as compared to the corona component, as black hole mass and Eddington ratio increase. (4) The X-ray spectral slopes of radio-quiet quasars display a non-monotonic trend with Eddington ratio, where the X-ray continuum softens with increasing Eddington ratio until L / L_{Edd} ~ 0.3, and then begins to harden. This observed non-monotonic trend may be caused by a change in the structure of the disk/corona system at L / L_{Edd} ~ 0.3, possibly due to increased radiation pressure. (5) The characteristic time scales of quasar optical flux variations increase with increasing M_{BH}, and are consistent with disk orbital or thermal time scales. In addition the amplitude of short time scale variability decreases with increasing M_{BH}. I interpret quasar optical light curves as being driven by thermal fluctuations, which in turn are driven by some other underlying stochastic process with characteristic time scale long compared to the disk thermal time scale. The stochastic model I use is able to explain both short and long time scale optical fluctuations.
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Uthas, Helena. "Observational studies of highly evolved cataclysmic variables." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/202889/.
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Cataclysmic Variables (CV) are binary systems where a main-sequence star transfers mass onto a white dwarf (WD). According to standard evolutionary theory, angular momentum loss drives CVs to initially evolve from longer to shorter orbital periods until a minimum period is reached (≈ 80 minutes). At roughly this stage, the donors becomes degenerate, expand in size, and the systems move towards longer orbital periods. Theory predicts that 70% of all CVs should have passed their minimum period and have sub-stellar donors, but until recently, no such systems were known. I present one CV showing evidence of harbouring a sub-dwarf donor, SDSS J1507+52. Due to the system’s unusually short orbital period of ≈ 65 minutes, and very high space velocity, two origins for SDSS J1507+52 have been proposed; either the system was formed from a young WD/brown-dwarf binary, or the system is a halo CV. In order to distinguish between these two theories, I present UV spectroscopy and find a metallicity consistent with halo origin. Systems close to the minimum period are expected to be faint and have low accretion rates. Some of these CVs show absorption in their spectra, implying that the underlying WD is exposed. This yields a rare opportunity to study the WD in a CV. I introduce two new systems showing WD signatures in their light curves and spectra, SDSS J1457+51 and BW Sculptoris. Despite the fact that CVs close to the minimum period should be faint, we find systems that aremuch too bright for their orbital periods. Such a system is T Pyxidis – a recurrent nova with an unusually high accretion rate and a photometrically determined period < 2 hours. The systemis ∼ 2 times brighter than any other CV at its period. However, to confirm the status of this unusual star, a more reliable period determination is needed. Here, I present a spectroscopic study of T Pyxidis confirming its evolutionary status as a short-period CV. In this thesis, I discuss what implications these systems may have on the current understanding of CV evolution, and the importance of studying individual systems in general
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Seigar, Marcus S. "Observational studies of the structure of spiral galaxies." Thesis, Liverpool John Moores University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242314.
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Nelson, Andrew Frederick. "Dynamics and observational appearance of circumstellar disks." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/288969.
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In my thesis I present a study of the dynamics and observational characteristics of massive circumstellar disks in two dimensions (r, φ) using two complimentary hydro-dynamic codes: a 'Smoothed Particle Hydrodynamic' (SPH) code and a 'Piecewise Parabolic Method' (PPM) code. I also study the detection limits available to radial velocity searches for low mass companions to main sequence stars. This thesis is organized as a series of published or submitted papers, connected by introductory and concluding material. I strongly recommend that readers of this abstract obtain the published versions of each of these papers. I first outline the progress which has been made in the modeling of the structure and origins of the solar system, then in chapter 2 (The Astrophysical Journal v502, p342, with W. Benz, F. Adams and D. Arnett), I proceed with numerical simulations of circumstellar disks using both hydrodynamic codes assuming a 'locally isothermal' equation of state. The disks studied range in mass from 0.05M* to 1.0 M* and in initial minimum Toomre Q value from 1.1 to 3.0. Massive disks (M(D) > 0.2 M*) tend to form grand design spiral structure with 1-3 arms, while low mass disks (M(D) ≤ 0.2M*) tend to form filamentary, > 4 armed spiral structures. In chapter 4 (submitted to The Astrophysical Journal with W. Benz and T. Ruzmaikina), I relax the assumption the locally isothermal evolution assumption and instead include simple heating and cooling prescriptions for the system. Under these physical conditions, the spiral arm growth is suppressed in the inner 1/3 of the disks relative to the isothermal evolution and in the remainder, changes character to more diffuse spiral structures. I synthesize spectral energy distributions (SEDs) from the simulations and compare them to fiducial SEDs derived from observed systems. The size distribution of grains in the inner disk can have marked consequences on the near infrared portion of the SED. After being vaporized in a hot midplane region, the grains do not reform quickly into the size distribution on which most opacity calculations are based. In chapter 6 (The Astrophysical Journal v500, p940 with Roger Angel), I examine the limits which may be placed upon the detection of planets, brown dwarfs and low mass stellar companions using radial velocity measurements. I derive an analytic expression describing the amplitude limits for periodic signals which may be obtained from a set of data of known duration, number of measurements and precision. In chapter 7, I outline several problems which may be profitably addressed by building on this work. (Abstract shortened by UMI.)
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Stempels, Henricus Cornelis. "An Observational Study of Accretion Processes in T Tauri Stars." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3420.
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Endicott, Thomas G. "Effect of Observational Cadence on Orbit Determination for Synthetic Near-Earth Objects." Thesis, University of Massachusetts Boston, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10617372.
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Near-Earth Objects (NEOs) are generally small, dark, and fast-moving. Multiple observations over time are necessary to constrain NEO orbits. Orbits based on observational data are inherently uncertain. Here we describe code written in Python and Fortran used to generate synthetic asteroids and compare calculated orbital fit based on noisy ephemeris using the a distance criteria, D-value. Observational sessions separated by more than one month produce very good orbital fits (low D-values) even at the highest noise level. Daily observational sessions show the highest D-values, as expected, since observed points on the orbital ellipse are not well separated. D-value is closely correlated to differences in the eccentricity and inclination of compared orbits.
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Moffat, Anthony F. J. "Observational overview of clumping in hot stellar winds." Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1763/.
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In the old days (pre ∼1990) hot stellar winds were assumed to be smooth, which made life fairly easy and bothered no one. Then after suspicious behaviour had been revealed, e.g. stochastic temporal variability in broadband polarimetry of single hot stars, it took the emerging CCD technology developed in the preceding decades (∼1970-80’s) to reveal that these winds were far from smooth. It was mainly high-S/N, time-dependent spectroscopy of strong optical recombination emission lines in WR, and also a few OB and other stars with strong hot winds, that indicated all hot stellar winds likely to be pervaded by thousands of multiscale (compressible supersonic turbulent?) structures, whose driver is probably some kind of radiative instability. Quantitative estimates of clumping-independent mass-loss rates came from various fronts, mainly dependent directly on density (e.g. electron-scattering wings of emission lines, UV spectroscopy of weak resonance lines, and binary-star properties including orbital-period changes, electron-scattering, and X-ray fluxes from colliding winds) rather than the more common, easier-to-obtain but clumping-dependent density-squared diagnostics (e.g. free-free emission in the IR/radio and recombination lines, of which the favourite has always been Hα). Many big questions still remain, such as: What do the clumps really look like? Do clumping properties change as one recedes from the mother star? Is clumping universal? Does the relative clumping correction depend on $dot{M}$ itself?
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Leverington, David. "The cost and citation-based effectiveness of observational astronomical facilities since 1958." Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363964.
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Shidatsu, Megumi. "Observational Studies of Accretion Disks in Black Hole X-ray Binaries." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199106.
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Ng, Shao-Chin Cindy. "Cosmological models with quintessence : dynamical properties and observational constraints." Title page, table of contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phn5758.pdf.
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Bibliography: leaves 100-106. Studies different models of "quintessence", in particular, a quintessence arising from an ultra-light pseudo Nambu-Goldstone boson. Overviews dynamical properties for these models using phase-space analyses to study attractor and tracker solutions. Studies high-redshift type Ia supernovae constraints on these models. Studies the impact of a simple phenomenological model for supernovae luminosity evolution on the PNGB models and the potentials of a future supernovae data set to discriminate the PNGB models over the other quintessence models. Studies gravitational lensing statistics of high luminosity quasars upon the quintessence models.
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Harding, Paul. "The formation of the Galactic bulge and halo: Observational signatures." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/289743.
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The evolution of tidal debris within the Galactic halo has been simulated to determine its detectability within the constraints imposed by currently available telescopes and instrumentation. Observations of the simulations show that there is a very high probability of detecting and quantifying the presence of tidal debris with a pencil beam survey of 100 square degrees. The debris is readily detectable via the presence of kinematic substructure in the radial velocities. The detection probabilities show surprisingly little change with the age of the debris. Accretion events that occurred up to ≳ 10 Gyr ago can be detected. In the limiting case of a single 10⁷ M(⊙) satellite contributing 1% of the luminous halo mass the detection probability is a few percent using just the velocities of 100 halo stars in a single 1 deg² field. The detection probabilities scale with the accreted fraction of the halo and the number of fields surveyed. Accurate CMDs in the Washington photometric system have been derived for four fields spanning the range of Galactocentric distances from 1.5 to 5.5 kpc. The differential reddening variations within each field were corrected by a new technique optimized for the highly variable reddening variations found in bulge fields. Abundance distributions in the four fields were derived from color-color diagrams in the Washington system. The quality of the photometry which yields photometric abundances with σ[Fe/H] ≲ 0.25 dex (including reddening errors) supplemented by the luminosity information from observations in the 51 filter allows contamination by foreground and background stars to be eliminated from the bulge sample. A clear abundance gradient is seen which is consistent with the change in morphology of the CMDs. The abundance gradient is predominantly due to a decrease in the fraction of stars in the metal-rich shoulder of the abundance distributions. The modal abundance changes little. Relative to Baade's window the magnitude distribution of clump stars in the L354 B-06 field implies a bar angle of ≃ 40 deg.
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Charnock, Tom. "Early universe cosmology and its observational effects on the cosmic microwave background." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/42164/.
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This Thesis is written in three parts. The first part describes the analytic calculation of the unequal-time correlator of cosmic strings and superstrings. The first efficient constraint analysis of all string and superstring network parameters is performed. By studying the effect of cosmic strings on the cosmic microwave background (CMB) radiation it is discovered that cosmic strings must make up a vanishingly small proportion of the energy density of the universe. The constraints on string network parameters are all skewed toward reducing the magnitude of energy density arising from strings. Also in this Part, a better comprehension of the unconnected segment model (USM) was gained. In particular, a greater understanding of the string scaling parameter $L_f$ was garnered, as well as finding the reason why the USM tends to provide greater power than simulations of Nambu-Goto cosmic strings. The second part contains a detailed description of statistical cosmology and how differences between parameter constraints from different data sets can lead to misleading quantification of discordance. The majority of this part describes different methods of quantifying differences between probability distributions and how these can be interpreted. In particular, using the most up-to-date data possible, differences between parameter constraints using the CMB and probes of large scale structure (LSS) in the universe can be measured. With current data the discordance can be interpreted as a low level of disagreement, but the application of prior ranges on well known parameters can force the tension to be greater. Using data from earlier work, this issue is considered in greater detail, with extensions to the accepted LCDM model added to test if the discordance can be alleviated. These extensions include the addition of active or sterile neutrinos and even ad-hoc changes to the primordial power spectrum. Although there are slight hints that these may help, when considering only the new data it might be unwise to believe that the discordance between parameter distributions from different data sets exists to a degree where the modifications are necessary. Finally, application of deep learning to astrophysical observations is discussed. Using neural networks to learn about specific problems is de rigueur and their use in astronomy and cosmology is a promising field of study. In particular, applying raw data to neural networks can often outperform, or add enhanced features, to what is possible with current, non-empirical feature detection. The classification of supernovae from their light curves can be achieved using a specific machine learning architecture called a recurrent neural network (RNN). Using the raw data from supernova light curves, the RNN is able to learn about features in sequences which can be used to classify types of supernova. Although a large training set is needed to perform as well as current techniques, one major advantage the RNN method has is the possibility of early detection. Rather than needing the entire light curve to perform statistical fits to categorise the supernova type, relatively little information from the early observation data is needed to classify using the RNN. Installing RNN on machinery for observation would save a vast amount of time by early classification since only supernovae of interest can be concentrated on.
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Savage, Chandra Shannon. "Ions, isotopes, and metal cyanides: Observational and laboratory studies." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/290082.
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Chemistry in the interstellar medium is very different from the processes which take place in terrestrial settings. Environments such as circumstellar envelopes, molecular clouds, and comets contain diverse and complex chemical networks. The low temperatures (10-50 K) and densities (1-10⁶ cm⁻³) allow normally unstable molecules to exist in significant quantities. At these temperatures, the rotational energy levels of molecules are populated, and thus these species can be detected by millimeter-wave radio astronomy. The detection and quantification of interstellar molecules, including metal cyanides and molecular ions, is the basis of this dissertation work. While conducting observations of CN and ¹³CN to determine the ¹²C/¹³C ratio throughout the Galaxy, it was found that the ratios in photon-dominated regions (PDRs) were much higher than those in nearby molecular clouds. This can be explained by isotope-selective photodissociation, in which the ¹²CN molecules are self-shielded. However, the chemistry in these regions is poorly understood, and other processes may be occurring. In order to understand one of the chemical networks present in PDRs, observations of HCO⁺, HOC⁺, and CO⁺ were made toward several of these sources. Previous studies indicated that the HCO⁺/HOC⁺ ratio was much lower in PDRs, due to the presence of CO⁺. The new observations indicate that there is a strong correlation between CO⁺ and HOC⁺ abundances, which suggests that other molecular ions which have not been detected in molecular clouds may be present in PDRs. There is a significant obstacle to the detection of new interstellar molecular ions, however. The laboratory spectra are virtually unknown for many of these species, due to their inherent instability. Thus, techniques which can selectively detect ionic spectra must be utilized. One such method is velocity modulation, which incorporates an AC electrical discharge to produce and detect ions. Previously, velocity modulation spectroscopy was employed only at infrared wavelengths. The final phase of this dissertation work was to design, build and test a velocity modulation spectrometer which functions at millimeter/sub-mm wavelengths. This system was then used to measure the previously unknown pure rotational spectrum of SH⁺ (X3Σ⁻).
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Davidson, James W. Jr. "A New Era of Observational Capability at Ritter Observatory: Spectropolarimetry from Exoplanets to Circumstellar Disks and Beyond." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1365171803.
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Trilling, David Eric. "A theoretical and observational study of the formation and evolution of planetary systems and extrasolar planets." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/288998.
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The recent discoveries of extrasolar giant planets (planets like Jupiter orbiting other stars like our Sun) at small distances from their central stars have revitalized the fields of planet and planetary system formation. The discoveries have overturned the former paradigm for planetary system formation which suggested that all planetary systems would look like our Solar System: these decidedly do not. The new view is that the early solar system was not nearly the quiescent place previously thought, but rather a dynamic environment in which planets are both easily created and easily destroyed. I have participated in the building of a new paradigm of planetary system formation, and this thesis describes theoretical and observational work which have contributed to this field. My theoretical work on the migration of giant planets from their formation location to distances close to their central star is described. I show that giant planets can reside at a range of heliocentric distances and masses, and we reproduce the distribution of observed giant planets, as well Jupiter. Using this model, I have predicted what the rate of planet formation must be, and what the initial, mass function for forming planets must be, in order to reproduce the observed planets. I also place some constraints on the mass and viscosity of the circumstellar disk out of which planets form. I show that giant planets close to their central stars are tidally stable, and stable against atmospheric loss, contrary to intuition. I predict that tidally stripped rocky cores, the remnants of giant planets, should exist at small heliocentric distances, a byproduct of the migration and mass loss that a majority of giant planets go through. Lastly, as an outgrowth of our migration work, I designed an observing program to search for circumstellar disks around stars with known extrasolar planets. I have detected three such disks, analogs to our Solar System's Kuiper Belt, and failed to detect disks around three other stars with extrasolar planets. I discuss my observing results, and the implications of detecting disks around some, but not all, of the stars with extrasolar planets I have looked at. In the conclusions and future work, I describe how this work forms a coherent part of a larger goal of understanding how, where, and how often planets and planetary systems form, answering the question of the origin, nature, and uniqueness of our Solar System.
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Friedman, Andrew. "Infrared Light Curves of Type Ia Supernovae." Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10116.
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This thesis presents the CfAIR2 data set, which includes over 4000 near-Infrared (NIR) \(JHK_s\)-band measurements of 104 Type Ia Supernovae (SN Ia) observed from 2005-2011 using PAIRITEL, the 1.3-m Peters Automated InfraRed Imaging TELescope at the Fred Lawrence Whipple Observatory (FLWO) on Mount Hopkins, Arizona. While the discovery of dark energy and most subsequent supernova cosmology has been performed using optical and Ultraviolet wavelength observations of SN Ia, a growing body of evidence suggests that NIR SN Ia observations will be crucial for future cosmological studies. Whereas SN Ia observed at optical wavelengths have been shown to be excellent standardizeable candles, using empirical correlations between luminosity, light curve shape, and color, the CfAIR2 data set strengthens the evidence that SN Ia at NIR wavelengths are essentially standard candles, even without correction for light-curve shape or for reddening. CfAIR2 was obtained as part of the CfA Supernova Program, an ongoing multi-wavelength follow-up effort at FLWO designed to observe high-quality, densely sampled light curves and spectra of hundreds of low-redshift SN Ia. CfAIR2 is the largest homogeneously observed and processed NIR data set of its kind to date, nearly tripling the number of individual \(JHK_s\) band observations and nearly doubling the set of SN Ia with published NIR light curves in the literature. Matched only by the recently published Carnegie Supernova Project sample, CfAIR2 complements the large and growing set of low-redshift optical and NIR SN Ia observations obtained by the CfA and other programs, making this data set a unique and particularly valuable local universe anchor for future supernova cosmology.Astronomy
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Kilpatrick, Charles Donald, and Charles Donald Kilpatrick. "New Observational Insight on Shock Interactions Toward Supernovae and Supernova Remnants." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621574.
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Supernovae (SNe) are energetic explosions that signal the end of a star's life. These events and the supernova remnants (SNRs) they leave behind play a central role in stellar feedback by adding energy and momentum and metals to the interstellar medium (ISM). Emission associated with these feedback processes, especially atomic and molecular line emission as well as thermal and nonthermal continuum emission is known to be enhanced in regions of high density, such as dense circumstellar matter (CSM) around SNe and molecular clouds (MCs). In this thesis, I begin with a brief overview of the physics of SN shocks in Chapter 1, focusing on a foundation for studying pan-chromatic signatures of interactions between SNe and dense environments. In Chapter 2, I examine an unusual SN with signatures of CSM interaction in the form of narrow lines of hydrogen (Type IIn) and thermal continuum emission. This SN appears to belong to a class of Type Ia SNe that shares spectroscopic features with Type IIn SNe. I discuss the difficulties of decomposing spectra in a regime where interaction occurs between SN ejecta and CSM, potentially confusing the underlying SN type. This is followed by a discussion of rebrightening that occurred at late-time in 𝐵 and 𝑉 band photometry of this SN, possibly associated with clumpy or dense CSM at large distances from the progenitor. In Chapter 3, I examine synchrotron emission from Cassiopeia A, observed in the 𝐾ₛ band over multiple epochs. The synchrotron emission is generally diffuse over the remnant, but there is one location in the southwest portion of the remnant where it appears to be enhanced and entrained as knots of emission in the SNR ejecta. I evaluate whether the 𝐾ₛ band knots are dominated by synchrotron emission by comparing them to other infrared and radio imaging that is known to be dominated by synchrotron emission. Concluding that they are likely synchrotron-emitting knots, I measure the magnetic field strength and electron density required for their evolution over the ~ 10 yr baseline they were observed and find 𝐵 ≈ 1.3-5.8 mG and 𝑛ₑ≈ 1,000-15,000 cm⁻³. The magnetic field strengths appear enhanced beyond values required by the adiabatic strong shock limit, arguing in favor of other forms of magnetic field amplification in the shock. In Chapter 4, I again discuss Cassiopeia A and interaction between the remnant and nearby MCs as seen at mid-infrared and millimeter wavelengths. I report detection of a SNR-MC interaction and analyze its signatures in broadened molecular lines. I extend this analysis in Chapter 5 to a large survey for SNR-MC interactions in the ¹²CO 𝐽=2-1 line. Although broadened ¹²CO 𝐽=2-1 line emission should be detectable toward virtually all SNR-MC interactions, I find relatively few examples; therefore, the number of interactions is low. This result favors mechanisms other than supernova feedback as the basic trigger for star formation. In addition, I find no significant association between TeV gamma-ray sources and MC interactions, contrary to predictions that SNR-MC interfaces are the primary venues for cosmic ray acceleration. I end this dissertation in Chapter 6 with a brief summary of my results and two extensions of this work: examining the late-time radio light curves of CSM-interacting SNe for signatures of radio synchrotron emission and dense or clumpy CSM at large distances from the progenitor and re-observing SNR-MC interactions in ¹²CO 𝐽=3-2 in order to verify the presence of shock-heated molecular gas and perform a census on the densities and temperatures of post-shock molecular gas.
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Williams, Rik Jackson. "The warm-hot environment of the Milky Way." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1154972702.
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Sjöbom, Ludvig. "The ultraviolet spectral slope of high-redshift galaxies." Thesis, Uppsala universitet, Observationell astrofysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-310603.
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The slope of the ultraviolet continuum emissions from a galaxy between 1250 and 2600 Å provides insights about several facets of the galaxy. Mainly, it is well-correlated with the amount of dust. This work presents a search for objects whose UV-continuum slopes are excessively steep, as well as suggestions for follow-up. The method used is looking through existing data sets, and proposing follow-up of the outliers in the distribution of slopes. Close to fifteen objects with slopes beyond what is easily explained by theory are presented. Since these lie beyond the realm of current theories, confirmations of these may hint at more extreme stellar populations than those currently known. This may include excessively metal-poor stars such as population III stars, or stellar populations where the initial mass function (IMF) for some reason may be biased towards massive stars. Steeper slopes are in general indicative of a lack of dust and an abundance of hot, blue stars; this is due to the reddening caused by dust, and emissions from cooler stars being peaked at longer wavelengths.
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Zack, Lindsay Nicole. "Laboratory and Observational Studies of Transient Molecules at Microwave and Millimeter/Submillimeter Wavelengths." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/217089.
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In this dissertation, techniques of high-resolution rotational spectroscopy have been used to measure the spectra of molecules in both laboratory and astronomical settings. In the laboratory, small metal-bearing molecules containing zinc, iron, nickel, titanium, yttrium, and scandium have been studied at microwave and millimeter/submillimeter wavelengths in order to determine their rotational, fine, and hyperfine constants. These molecules were synthesized in situ in direct-absorption and Fourier-transform microwave spectrometers using Broida-type ovens and laser ablation methods. From the spectroscopic parameters, information about fundamental physical propertes and electronic character could be obtained. Radio telescopes were used to measure the spectra of molecules in different interstellar environments. A new molecule, FeCN, was detected toward the circumstellar envelope of the carbon-rich asymtotic giant branch star, IRC+10216, marking the first iron-bearing molecule detected in the interstellar medium. The telescopes were also used to conduct a study of the evolved planetary nebula, NGC 7293, or the Helix Nebula. In the Helix, CO, HCO⁺, and H₂CO were observed at several positions offset from the central star to obtain densities and kinetic temperatures throughout the Helix. A map of the HCO⁺ J = 1→ 0 transition was also constructed, showing that HCO⁺ is widespread throughout the Helix, instead of being photodissociated and destroyed, as theoretical models of planetary nebulae predict.
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Namekata, Kousuke. "Observational Studies of Extreme Stellar Magnetic Activities: Spots, Flares, and Mass Ejections." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263473.
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Johnson, Elsa M. 1971. "Host stellar population properties and the observational selection function of type Ia supernovae." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/11297.
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xlix, 348 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.Supernovae Ia are viable standard candles for measuring cosmological distances because of their enormous light output and similar intrinsic brightness. However, dispersion in intrinsic brightness casts doubt on the overall reliability of supernovae as cosmological distance indicators. Moreover, as shown in this thesis, the dependence of peak brightness on host galaxy properties significantly contributes to this dispersion. As a result, there is good reason to doubt that the nearby sample of supernovae Ia is identical to the distant samples, which occur in host galaxies that are billions of years younger. This study explores the validity of supernovae Ia as standard candles by examining regions of nearby galaxies that hosted supernovae and modeling their observational selection function. The approach is two-fold. First, photometry is performed on the stellar population environment of supernovae to characterize that region as a function of supernova type. Then, the observational selection function is simulated to determine the true supernovae production rate of the z < 0.1 redshift limit. We find that, on average, type Ia events occur in redder and older populations; underluminous supernovae Ia occur in regions that seem to be preferentially dusty, whereas normal Ia coming from the same galaxy type occur in a wide range of extinction environments. Furthermore, redder peak colors correspond to redder underlying population colors. This finding implies that dust extinction effects can cause systematic errors in the luminosity calibration of Ia events Finally, a single supernova rate does not adequately describe all supernovae Ia within z < 0.1. A rate of 0.25 SNu describes the population up to z < 0.03, and a much smaller rate, 0.1 SNu or less, describes supernovae past this distance. This finding indicates that observed supernova rates per galaxy remain biased by sample selection effects and that the intrinsic rate is likely uncertain by a factor of 2 to 3.
Committee in charge: Raymond Frey, Chairperson, Physics; James Imamura, Member, Physics; Gregory Bothun, Member, Physics; Stephen Hsu, Member, Physics; James Isenberg, Outside Member, Mathematics
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Kelvin, Lee Steven. "The structure of galaxies : the division of stellar mass by morphological type and structural component." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3689.
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The mechanisms which cause galaxies to form and evolve each leave behind distinct structural markers in their wake. Dynamically hot processes (e.g., monolithic collapse, hierarchical merging) give rise to pressure-supported spheroidal structures, including elliptical galaxies and classical bulges. By contrast, dynamically cold processes (e.g., gas accretion, AGN splashback) lead to flattened rotationally-supported disk-like structures, often found on their own or as part of a spiral galaxy. If left in isolation for a sufficient length of time, secular evolutionary processes cause the formation of a bar-like structure within the disk, precipitating the genesis of a rotationally-supported pseudo-bulge. Robustly measuring galaxy structure enables us to ascertain the relative importance of these competing evolutionary mechanisms and; in so doing, help broaden our understanding of how the Universe around us came to be. This thesis explores the relation between galaxy structure, morphology and stellar mass. In the first part I present single-Sérsic two-dimensional model fits to 167,600 galaxies modelled independently in the ugrizYJHK bandpasses using reprocessed Sloan Digital Sky Survey Data Release Seven (SDSS DR7) and UKIRT Infrared Deep Sky Survey Large Area Survey (UKIDSS LAS) imaging data available via the Galaxy and Mass Assembly (GAMA) data base. In order to facilitate this study, we developed Structural Investigation of Galaxies via Model Analysis (SIGMA): an automated wrapper around several contemporary astronomy software packages. We confirm that variations in global structural measurements with wavelength arise due to the effects of dust attenuation and stellar population/metallicity gradients within galaxies. In the second part of this thesis we establish a volume-limited sample of 3,845 galaxies in the local Universe and visually classify these galaxies according to their morphological Hubble type. We find that single-Sérsic photometry accurately reproduces the morphology luminosity functions predicted in the literature. We employ multi-component Sérsic profiling to provide bulge-disk decompositions for this sample, allowing for the luminosity and stellar mass to be divided between the key structural components: spheroids and disks. Grouping the stellar mass in these structures by the evolutionary mechanisms that formed them, we find that hot-mode collapse, merger or otherwise turbulent mechanisms account for ~46% of the total stellar mass budget, cold-mode gas accretion and splashback mechanisms account for ~48% of the total stellar mass budget and secular evolutionary processes for ~6.5% of the total stellar mass budget in the local (z<0.06) Universe.
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Zach, Juergen Johann. "Observational Signatures of the Macroscopic Formation of Strange Matter during Core Collapse Supernovae." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1053470113.
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Hamacher, Duane Willis Physics Faculty of Science UNSW. "A search for transiting extrasolar planets from the southern hemisphere." Publisher:University of New South Wales. Physics, 2008. http://handle.unsw.edu.au/1959.4/40943.
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To date, more than 300 planets orbiting stars other than our sun have been discovered using a range of observing techniques, with new discoveries occuring monthly. The work in this thesis focused on the detection of exoplanets using the transit method. Planets orbiting close to their host stars have a roughly 10 per cent chance of eclipsing (transiting) the star, with Jupiter?sized planets causing a one per cent dip in the flux of the star over a few hours. A wealth of orbital and physical information on the system can be extracted from these systems, including the planet density which is essential in constraining models of planetary formation. To detect these types of planets requires monitoring tens of thousands of stars over a period of months. To accomplish this, we conduct a wide-field survey using the 0.5-meter Automated Patrol Telescope (APT) at Siding Spring Observatory (SSO) in NSW, Australia. Once candidates were selected from the data?set, selection criteria were applied to separate the likely planet candidates from the false?positives. For this thesis, the methods and instrumentation used in attaining data and selecting planet candidates are discussed, as well as the results and analysis of the planet candidates selected from star fields observed from 2004?2007. Of the 65 planet candidates initially selected from the 25 target fields observed, only two were consistent with a planet transit. These candidates were later determined to be eclipsing binary stars based on follow up observations using the 40-inch telescope, 2.3-m telescope, and the 3.9-m Anglo-Australian Telescope, all located at SSO. Additionally, two planet candidates from the SuperWASP-North consortium were observed on the 40-inch telescope. Both proved to be eclipsing binary stars. While no planets were found, our search methods and results are consistent with successful transit surveys targeting similar fields with stars in a similar magnitude range and using similar methods.
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Donevski, Darko. "Identification et modélisation des galaxies distantes dans les relevés cosmologiques du satellite Herschel." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0323/document.
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La population de galaxies poussiéreuses ayant un fort taux de formation stellaire (Dusty Star Forming Galaxies, DSFGs) joue un rôle très important dans l’histoire de l’univers, avec des taux de formation d’étoiles allant de quelques centaines à quelques milliers de masses solaires par an. Les sondages infrarouges, comme ceux entrepris à l’aide du satellite Herschel, nous offrent l’opportunité de recenser de manière approfondie ces DSFGs jusqu’à de grands décalages spectraux. Cependant, jusqu’à présent seul un petit nombre de DSFG détecté par Herschel ont été confirmés pour être à des décalages spectraux supérieurs à 4. Les modèles de formation et d’évolution des galaxies stipulent généralement que la population de DSFG à z > 4 sont les progéniteurs des galaxies elliptiques, observées dans les amas les plus massifs de l’univers local. L’abondance des DSFGs à z > 4 se révèle donc être décisive pour contraindre ces modèles ainsi que pour vérifier notre compréhension globale de l’univers lointain. Le premier objectif de mon travail de recherche est d’identifier les candidates galaxies à z > 4 détectées sur des champs les plus larges possibles observés par Herschel et l’instrument SPIRE et d’examiner les propriétés statistiques de celles-ci. A cette fin, j’ai créé un nouvel algorithme de sélection dans le but d’augmenter substantiellement le nombre de candidates et de comprendre leur natureOver the last few decades, great progress has been made in our understanding of the star formation history of the Universe. With the discovery of distant, dusty star-forming galaxies (DSFGs) it has become apparent that observing at rest-frame UV and optical wavelengths is insufficient as a large fraction of the star formation is dust obscured. Thanks to the extensive observational studies carried out during the last two decades, we learn that DSFGs have a redshift peak at z ∼ 2, matching the cosmic time where galaxies have formed most of their young, massive stars. However, it remains extremely challenging to use the Herschel space observatory for identifying a tail extending towards much higher redshifts (z > 4). As a result, until recently only a small number of infrared-selected DSFGs at z > 4 were known, most of them strongly gravitationally lensed. One of the main goals of this Thesis is to assemble candidate z > 4 galaxies detected in a large area survey observed by Herschel-SPIRE and to examine the statistical properties and environments of these systems
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Johnston, Katharine G. "Observational signatures of massive star formation : an investigation of the environments in which they form, and the applicability of the paradigm of low-mass star formation." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1895.
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This thesis presents both a study of the cluster-scale environments in which massive stars form, investigating in particular how the ionized gas in these regions relates to the molecular star-forming material, as well as detailed studies of two luminous forming stars, AFGL 2591 and IRAS 20126+4104, to determine whether they are forming similarly to their low-mass counterparts. The results of this work include the identification of 35 HII regions (20 newly discovered) via a radio continuum survey of ionized gas towards 31 molecular cluster-forming clumps. The observed ionized gas was found to be preferentially associated with the clumps, which were shown to have a range of evolutionary stages. The massive star formation efficiency was determined for the clumps with associated ionized gas, and a relationship was found between the mass of the clumps and the mass of their embedded massive stars. By modelling the SEDs and images of AFGL 2591 and IRAS 20126+4104, it was found that the geometry of their circumstellar material was generally consistent with an envelope plus disk, similar to that expected for low-mass protostars. However, within the central ~1800 AU, the mid-IR images of IRAS 20126+4104 were better described by only a flattened envelope, suggesting that the radiation from IRAS 20126+4104 may be affecting the regions closest to the star. Observations of the ionized and molecular gas towards AFGL 2591 were carried out, and a photoionization code was developed to interpret these observations. The results showed that the observed 3.6 cm emission is likely to be produced by both a shock-ionized jet and a hypercompact HII region that does not appear to have disrupted the jet or the large-scale circumstellar environment. In addition, the C¹⁸O(1-0) emission observed towards AFGL2591 traces the densest parts of the outflow, with the blue-shifted emission exhibiting many of the properties of the outflows from low-mass protostars.
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Abbas, Mohamad. "A search for Long-Period Variable Stars in the Globular Cluster NGC 6496." Bowling Green State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1308597257.
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Kager, Elisabeth. "Pulsation Properties of Long Period Variable Stars in Globular Cluster NGC 6553." Bowling Green State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1277148078.
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Suchyta, Eric Daniel. "Embrace the Dark Side: Advancing the Dark Energy Survey." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440098241.
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Court, A. J. "Hard X-ray astronomy from balloon altitudes." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377796.
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Zadrozny, Andrew. "Spectroscopic techniques and observations in infrared astronomy." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46625.
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Garcia, Garcia Carlos. "Theories of gravitation confronted with cosmological observations." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/670878.
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This thesis studies Dark Energy, a central topic of Modern Cosmology, from different points of view. It covers from models and parametrizations to likelihood approximations for the observations of the Large Scale Structure (LSS) of the Universe, which are vital for model constraining, as well as for our study of the S8 tension.
The studied model is the α-attractors dark energy model, which reproduces current observations thanks to its capability to mimic a cosmological constant. It is inspired on the Planck-favored inflationary class of models α-attractors and links the inflationary and dark energy periods with the same scalar field. Fortunately, next-generation surveys might be able to distinguish it from ΛCDM by up to 3σ of confidence.
Nevertheless, in order to make the most of forthcoming data, we need a formalism that allows us to test models in an efficient way. This could be a observational and theoretical constrained parametrization. We show the case of w0 -wa for thawing quintessence. This parametrization is able to reproduce the observables from recombination to the present when chosen smartly. In addition, their probability distributions built from purely theoretical considerations allow us to restrict the observational bounds to the theoretically motivated area. This work shows how we can work with very general theories such as Horndeski.
However, the observational constraints also depend on the correct estimation of their likelihood. Therefore, we have developed (and implemented in NaMaster, from LSST DESC) the Narrow Kernel Approximation (NKA) for the Gaussian (not causally connected) part of the LSS pseudo-Cl covariance matrix. This allows to reproduce accurately the cosmological parameters’ posterior distribution while reducing the computational cost from O(lmax6) (exact computation) to O(lmax3). For sure, the exact computation will be intractable for the next-generation LSS observations, which will resolve really small scales.
The NKA has allowed us to start our study of the origin of the S8 tension reported by KiDS-450. With data of LSS from DES and data of CMB from Planck, we want to obtain the temporal evolution of S8 and compare it with that given by KiDS-450 data.
Summing up, this thesis has covered dark energy models and developed accurate methods to test their viability in an efficient way. Furthermore, it has gone closer to data and developed the NKA that allows to accurately estimate the LSS likelihood, making it possible for us to study the origin of the S8 tension.Esta tesis estudia la energía oscura, un tema central en la Cosmología Moderna, desde diferentes puntos de vista. Cubre desde modelos y parametrizaciones, hasta aproximaciones de la likelihood de observaciones de la Estructura a Gran Escala del Universo (LSS), vitales para constreñir los modelos, como para nuestro estudio de la tensión en S8. El modelo estudiado es el de energía oscura de α-attractors, que reproduce las observaciones actuales al poder asemejarse a una constante cosmológica. Inspirado en la clase de modelos de inflación favorecidos por Planck, α-attractors, enlaza el periodo de inflación y energía oscura mediante el mismo campo escalar. Afortunadamente, las misiones futuras podrían diferenciarlo de ΛCDM con hasta 3σ de confianza. No obstante, aprovechar al máximo los datos futuros requiere un formalismo que nos permita comprobar la viabilidad de los modelos eficientemente, como una parametrización acotada observacional y teóricamente. Mostramos el caso de w0-wa para quintaesencia de tipo thawing, que reproduce los observables desde recombinación hasta hoy, si se eligen apropiadamente. Construidas sus distribuciones de probabilidad bajo condiciones puramente teóricas, nos permiten restringir las cotas observacionales a la zona teóricamente motivada. Este trabajo es una muestra de cómo podemos trabajar con teorías muy generales como Horndeski. Pero las cotas observacionales dependen también de una correcta estimación de su likelihood. Por ello, hemos desarrollado (e implementado en NaMaster, del LSST DESC) la Narrow Kernel Approximation (NKA) para la parte gausiana (causalmente no conectada) de la covarianza de los pseudo-Cl de LSS. Ésta permite obtener con exactitud las cotas en los parámetros cosmológicos, al tiempo que reduce el coste computacional de O(lmax⁶) (cómputo exacto) a O(lmax3). Claramente, el cómputo exacto es inviable para las observaciones futuras de LSS que resolverán escalas muy pequeñas. La NKA nos ha permitido empezar a estudiar el origen de la tensión en S8 reportada por KiDS-450. Con datos de LSS de DES y del CMB de Planck, pretendemos obtener la evolución temporal de S8 y compararla con la dada por los datos de KiDS-450. En resumen, esta tesis ha trabajado en modelos de energía oscura y desarrollado métodos precisos para comprobar su viabilidad de manera eficiente. Además, se ha acercado a los datos y desarrollado la NKA que permite estimar precisamente la likelihood para LSS; permitiéndonos estudiar el origen de la tensión en el parámetro S8.
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Alp, Dennis. "Core-collapse Supernovae : Theory vs. Observations." Licentiate thesis, KTH, Partikel- och astropartikelfysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-241431.
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A core-collapse supernova (CCSN) is an astronomical explosion that indicates the death of a massive star. The iron core of the star collapses into either a neutron star or a black hole while the rest of the material is expelled at high velocities. Supernovae (SNe) are important for the chemical evolution of the Universe because a large fraction of the heavier elements such as oxygen, silicon, and iron are liberated by CCSN explosions. Another important role of SNe is that the ejected material seed the next generation of stars and planets. From observations, it is clear that a large fraction of all massive stars undergoes SN explosions, but describing how SNe explode has remained a challenge for many decades. The attached papers focus on comparing theoretical predictions with observations, primarily observations of SN 1987A. The compact remnant in SN 1987A has not yet been detected and we have investigated how a compact object can remain hidden in the ejecta (Paper I and II). Because of the high opacity of the metal-rich ejecta, the direct X-ray observations are not very constraining even for potentially favorable viewing angles. However, the combined observations still strongly constrain fallback accretion and put a limit on possible pulsar wind activity. The thermal surface emission from a neutron star is consistent with the observations if our line of sight is dust-obscured, and only marginally consistent otherwise. Future observations provide promising opportunities for detecting the compact object. We have also compared the most recent three-dimensional neutrino-driven SN models that are based on explosion simulations with early X-ray and gamma-ray observations of SN 1987A (Paper III). The models that are designed to match SN 1987A fit the data well, but not all tensions can be explained by choosing a suitable viewing angle. More generally, the asymmetries do not affect the early emission qualitatively and different progenitors of the same class result in similar early emission. We also find that the progenitor metallicity is important for the low-energy X-ray cuto↵. Current instruments should be able to detect this emission from SNe at distances of 3–10 Mpc, which correspond to distances slightly beyond the Local Group.En kärnkollapssupernova (CCSN) är en astronomisk explosion som indikerar slutet av en massiv stjärnas liv. Stjärnans järnkärna kollapsar antingen till en neutronstjärna eller ett svart hål medan resten av materialet slungas iväg med höga hastigheter. Supernovor (SNe) är viktiga för Universums kemiska utveckling eftersom en stor andel av alla tyngre element såsom syre, kisel, och järn frigörs i CCSN-explosioner. Ytterligare en viktig roll för SNe är att nästa generations stjärnor och planeter bildas av det utkastade materialet. Från observationer är det tydligt att en stor andel av alla massiva stjärnor genomgår SN-explosioner, men att förklara hur SNe exploderar har kvarstått som en utmaning under flera decennier. De bifogade artiklarna fokuserar på att jämföra teoretiska förutsägelser med observationer, primärt observationer av SN 1987A. Det kompakta objektet i SN 1987A har ännu inte blivit detekterat och vi har undersökt hur ett kompakt objekt kan förbli dolt i ejektat (Paper I och II). De direkta röntgenobservationerna är inte så begränsande även längs potentiellt gynsamma siktlinjer på grund av det metallrika ejektats höga opacitet. Däremot begränsar kombinationen av alla observationer starkt ackretion och sätter en gräns för möjlig pulsarvindsaktivitet. Den termiska ytstrålningen från en neutronstjärna är konsistent med observationerna om vår siktlinje är skymd av stoft, och bara marginellt konsistent annars. Framtida observationer utgör lovande möjligheter för att detektera det kompakta objektet. Vi har också jämfört de senaste tredimensionella neutrinodrivna SN-modellerna, som är baserade på explosionssimuleringar, med tidiga röntgen- och gamma-observationer av SN 1987A (Paper III). SN 1987A-modellerna passar datan väl, men alla diskrepanser kan inte förklaras av ett lämpligt val av observationsvinkel. Generellt så påverkar inte asymmetrierna den tidiga emissionen kvalitativt och olika föregångarstjärnor av samma kategori resulterar i likartad strålning. Vi finner också att föregångarstjärnans metallisitet är viktig för egenskaperna av lågenergiröntgenstrålningen. Befintliga instrument borde kunna detektera denna emission på 3--10 Mpc, vilket motsvarar avstånd lite bortom den Lokala galaxhopen.
Examintor: Professor Mark PearceQC 20190121
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Zbinden, Jonas. "Planning Observations of Terrestrial ExoplanetsAround M Type Stars with CRIRES+." Thesis, Uppsala universitet, Observationell astrofysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-437673.
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In recent decades, thousands of exoplanets have been discovered. The next step is to characterize theobserved planets in terms of their radii, masses, density, physical conditions and composition of theiratmospheres. Several space-based observatories such as TESS and CHEOPS have started determiningthe first three observables but characterization of exoplanetary atmospheres is waiting for observationcampaigns with instruments like CRIRES+ at the VLT and NIRSpec on the JWST. To ensure the efficiencyof data acquisition, careful planning of observations is necessary. In this project we developeda software tool to select and rank candidates based on the feasibility of observations of atmosphericfeatures during transits with CRIRES+. We also review different techniques to retrieve transmissionspectra from transit observations and modeling of exoplanet atmospheres in order to clarify the requirementsfor the data. Our CRIRES-planning-tool is built on astronomical observation planningmethods from astropy and astroplan and the exposure time calculator designed for CRIRES+ byESO and UU. We conclude that observations for atmospheric characterization with CRIRES+ are feasible.However, we observed that for a robust candidate selection, careful iterative tuning of proposedconstraints is required.
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Myers, Richard Michael. "High spectral resolution gamma ray astronomy in the energy region 50keV to l0MeV." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6413/.
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Observations of the Crab nebula region and of the unusual active galaxy NGC1275 made during a balloon flight of the Durham high spectral resolution gamma ray telescope are described. From the Crab, spectral line fluxes were detected at 79 keV (transient), 405 keV, and at 1050 keV. The first two are possible confirmation of previous results. From NGC1275, evidence of two-photon electron-positron annihilation radiation with the expected redshifted energy of 502 keV was observed. Possible interpretations are suggested.
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Warell, Johan. "Regolith Properties of Mercury Derived from Observations and Modelling." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://publications.uu.se/theses/91-554-5535-2/.
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Hill, David T. "The optical and NIR luminous energy output of the Universe : the creation and utilisation of a 9 waveband consistent sample of galaxies using UKIDSS and SDSS observations with the GAMA and MGC spectroscopic datasets." Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/1696.
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Theories of how galaxies form and evolve depend greatly on constraints provided by observations. However, when those observations come from different datasets, systematic offsets may occur. This causes difficulties measuring variations in parameters between filters. In this thesis I present the variation in total luminosity density with wavelength in the nearby Universe (z<0.1), produced from a consistent reanalysis of NIR and optical observations, taken from the MGC, UKIDSS and SDSS surveys. I derive luminosity distributions, best-fitting Schechter function parameterisations and total luminosity densities in ugrizYJHK, and compare the variation in luminosity density with cosmic star formation history (CSFH) and initial mass function (IMF) models. I examine the r band luminosity distribution produced using different aperture definitions, the joint luminosity- surface brightness (bivariate brightness) distribution in ugrizYJHK, comparing them to previously derived distributions, and how the total luminosity density varies with wavelength when surface brightness incompleteness is accounted for. I find the following results. (1) The total luminosity density calculated using a non-Sersic (e.g. Kron or Petrosian) aperture is underestimated by at least 15%, (2) Changing the detection threshold has a minor effect on the best-fitting Schecter parameters, but the choice of Kron or Petrosian apertures causes an offset between datasets, regardless of the filter used to define the source list, (3) The decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag, and best-fitting Schechter parameters from total magnitude photometric systems have a flatter faint-end slope than Kron or Petrosian photometry, (4) There is no surface brightness distribution evolution with luminosity for luminous galaxies, but at fainter magnitudes the distribution broadens and the peak surface brightness dims. A Choloniewski function that is modified to account for this surface brightness evolution fits the bivariate-brightness distribution better than an unmodified Choloniewski function, (5) The energy density per unit interval, vf(v) derived using MGC and GAMA samples agrees within 90% confidence intervals, but does not agree with predictions using standard CSFH and IMF models. Possible improvements to the data and alterations to the theory are suggested.
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Turner, James Edmund Henry. "Astronomy with integral field spectroscopy : observation, data analysis and results." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/3765/.
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With a new generation of facility instruments being commissioned for 8 metre telescopes, integral field spectroscopy will soon be a standard tool in astronomy, opening a range of exciting new research opportunities. It is clear, however, that reducing and analyzing integral field data is a complex problem, which will need considerable attention before the full potential of the hardware can be realized. The purpose of this thesis is therefore to explore some of the scientific capabilities of integral field spectroscopy, developing the techniques needed to produce astrophysical results from the data. Two chapters are dedicated to the problem of analyzing observations from the densely-packed optical fibre instruments pioneered at Durham. It is shown that, in the limit where each spectrum is sampled by only one detector row, data maybe treated in a similar way to those from an image slicer. The properties of raw fibre data are considered in the context of the Sampling Theorem and methods for three dimensional image reconstruction are discussed. These ideas are implemented in an IRAF data reduction package for the Thousand Element Integral Field Unit (TEIFU), with source code provided on the accompanying compact disc. Two observational studies are also presented. In the first case, the 3D infrared image slicer has been used to test for the presence of a super-massive black hole in the giant early-type galaxy NGC 1316. Measurements of the stellar kinematics do not reveal a black hole of mass 5 x l0(^9)M©, as predicted from bulge luminosity using the relationship of Kormendy & Richstone (1995). The second study is an investigation into the origin of [Fell] line emission in the Seyfert galaxy NGC4151, using Durham University's SMIRFS-IFU. By mapping [Fell] line strength and velocity at the galaxy centre, it is shown that the emission is associated with the optical narrow line region, rather than the radio jet, indicating that the excitation is primarily due to photoionizing X-rays.Finally, a report is given on the performance of TEIFU, which was commissioned at the William Herschel Telescope in 1999. Measurements of throughput and fibre response variation are given and a reconstructed test observation of the radio galaxy 3C 327 is shown, demonstrating the functionality of the instrument and software.
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Tan, Boon Kok. "Development of coherent detector technologies for sub-millimetre wave astronomy observations." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:398fda64-e486-4917-b2e4-8e1dfe5d5c83.
Full textAbstract:
Superconductor-Insulator-Superconductor (SIS) mixers are now used regularly in sub- millimetre astronomical receivers. They have already achieved sensitivity approaching the quantum limit at frequencies below the superconducting gap of niobium (~680 GHz). Above that, the mixer performance is compromised by losses, unless materials with higher superconducting gap are employed in conjunction with the niobium tunnel junction. In this thesis, we present the development of 700 GHz niobium SIS mixers, employing a unilateral finline taper on a thin Silicon-On-Insulator (SOI) substrate. These mixers are broadband with full on-chip planar circuit integration, and require only a very simple mixer block. They were designed using rigorous 3-D electromagnetic simulator (HFSS), in conjunction with a quantum mixing software package (SuperMix), and have demonstrated good performance with the best noise temperature measured at 143 K. Our mixer devices were fed by multiple flare angle smooth-walled horns, which are easy to fabricated, yet retain the high performance of corrugated horns. The radiation patterns measured from 600–740 GHz have shown good beam circularity, low sidelobe and cross-polarization levels. In this thesis, we also present SIS mixer designs with balanced and sideband separ- ating capability. These mixers employ back-to-back finline tapers, so that the RF and local oscillator (LO) signals can be injected separately without a beam splitter. We have fabricated and tested the performance of the balanced mixers, and analysed their performance thoroughly. We have also investigated a new method of generating LO signals by beating the tones of two infrared lasers. Using the current 16-pixel 350 GHz SIS receiver, HARP-B, we have observed the 12CO J=3→2 emission lines from two nearby galaxies. An important result we found is that the 12CO J=3→2 correlates strongly with the 8 μm Polycyclic Aromatic Hydrocarbon emission.
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Paley, Elizabeth Sara 1967. "An infrared and optical study of bright IRAS point sources of minimum apparent temperature." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277118.
Full textAbstract:
A sample of 170 sources from the IRAS Point Source Catalog (PSC) havingb
≥ 40°, 100μm flux F₄ ≥ 2.5 Jy, and upper limit fluxes at 12, 25 and 60μm was studied on POSS and ESO photographic plates. 151 of these sources are identified as 'infrared cirrus,' thirteen as galaxies, and one as a planetary nebula; four sources lie in the Small Magellanic Cloud (SMC), and the remaining source is Saturn. Accurate infrared fluxes were obtained for 29 cirrus sources, the galaxies, and the planetary nebula. The colors of the cirrus sources support the hypothesis that the radiation is coming from a mixture of large, cool grains and Polycyclic Aromatic Hydrocarbons (PAHs), with large variation in relative abundances. Optical colors and surface brightness were obtained for one cirrus cloud using data from the CCD Transit Instrument on Kitt Peak.
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de, la Cruz Rodríguez Jaime. "Measuring the solar atmosphere." Doctoral thesis, Stockholms universitet, Institutionen för astronomi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-43646.
Full textAbstract:
The new CRISP filter at the Swedish 1-m Solar Telescope provides opportunities for observing the solar atmosphere with unprecedented spatial resolution and cadence. In order to benefit from the high quality of observational data from this instrument, we have developed methods for calibrating and restoring polarized Stokes images, obtained at optical and near infrared wavelengths, taking into account field-of-view variations of the filter properties. In order to facilitate velocity measurements, a time series from a 3D hydrodynamical granulation simulation is used to compute quiet Sun spectral line profiles at different heliocentric angles. The synthetic line profiles, with their convective blueshifts, can be used as absolute references for line-of-sight velocities. Observations of the Ca II 8542 Å line are used to study magnetic fields in chromospheric fibrils. The line wings show the granulation pattern at mid-photospheric heights whereas the overlying chromosphere is seen in the core of the line. Using full Stokes data, we have attempted to observationally verify the alignment of chromospheric fibrils with the magnetic field. Our results suggest that in most cases fibrils are aligned along the magnetic field direction, but we also find examples where this is not the case. Detailed interpretation of Stokes data from spectral lines formed in the chromospheric data can be made using non-LTE inversion codes. For the first time, we use a realistic 3D MHD chromospheric simulation of the quiet Sun to assess how well NLTE inversions recover physical quantities from spectropolarimetric observations of Ca II 8542 Å. We demonstrate that inversions provide realistic estimates of depth-averaged quantities in the chromosphere, although high spectral resolution and high sensitivity are needed to measure quiet Sun chromospheric magnetic fields.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Manuscript. Paper 3: Submitted. Paper 4: Submitted.
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Devogèle, Maxime. "Propriétés des astéroïdes de type L : un lien avec le Système Solaire primordial ?" Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4069/document.
Full textAbstract:
En 2006, Il a été observé que l'astéroïde (234)~Barbara possède une valeur anormalement élevée d’angle d’inversion polarimétrie. Par la suite, d'autres astéroïdes possédant la même caractéristique que Barbara ont été découverts et nommés ``Barbarians'' en référence à (234) Barbara. L'étude de ces astéroïdes constitue le sujet principal de cette thèse ayant pour but de mieux comprendre la raison de cet angle d'inversion plus élevé que la normale. La première hypothèse formulée afin d’expliquer cette anomalie polarimétrique suppose que les astéroïdes Barbarians possèdent une forme fortement irrégulière induisant une réponse polarimétrique particulière. La deuxième hypothèse stipule que les astéroïdes Barbarians possèdent une abondance anormalement élevée d'inclusions riches en aluminium et en calcium. Au cours de cette thèse, nous avons obtenu de nombreuses nouvelles données aussi bien en photométrie, spectroscopie que polarimétrie. Ces nouvelles observations d’astéroïdes ont permis de tester différentes hypothèses formulées précédemment afin d'expliquer l'anomalie polarimétrique observée. Nos observations ont permis d'éliminer une hypothèse faisant appel à une topologie particulière des astéroïdes Barbarians, mais nous avons confirmé et renforcé une autre hypothèse faisant intervenir une composition particulière de ces astéroïdes. Si cette dernière hypothèse était confirmée, cela en ferait des astéroïdes primitifs s'étant formés lors des premières étapes du Système Solaire. Leur étude permettrait donc d'en apprendre plus sur les mécanismes de formation des astéroïdes et la composition de la nébuleuse ayant donné naissance au Système Solaire. Comprendre les astéroïdes Barbarians sert à mieux comprendre les premières étapes de formation du Système Solaire et aussi celles des planètesA few years ago, asteroid polarimetry allowed to discover a class of asteroids exhibiting peculiar phase polarization curves, collectively called "Barbarians" from the prototype of this class, the asteroid (234) Barbara. All such objects belong to the L visible plus near infrared based taxonomic class. The anomalous polarization has been tentatively interpreted in terms of high-albedo, spinel-rich Calcium-Aluminum inclusions (CAI) that could be abundant on the surfaces of some of these asteroids, according to their spectral reflectance properties and to analogies with CO3/CV3 meteorites. Such CAIs are among the oldest mineral assemblages ever found in the Solar System. Barbarians' surfaces could therefore be rich in this very ancient material and bring information on the early phases of planetary formation. During this thesis, a systematic campaign for photometric, polarimetric and spectroscopic characterization has been conducted. These observation campaigns allowed improving our general knowledge about these peculiar asteroids and highlighting the link between polarization and polarimetric properties. Our observation also allowed discarding the hypotheses involving peculiar shape for these asteroids. However, as it was suggested, a link between the presence of CAI and the polarimetric response was found. Our observations show that the relative abundance of CAI is correlated with the polarimetric inversion angle. This is the first time that a direct link between polarimetric and spectroscopic properties is found
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Moldón, Vara Francisco Javier. "Structure and nature of gamma-ray binaries by means of VLBI observations." Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/96996.
Full textAbstract:
Gamma-ray binaries are extreme systems that produce non-thermal emission from radio to very-high-energy (above TeV) gamma rays, with the energy output in the spectral energy distribution (SED) dominated by the MeV–GeV photons. Their broadband emission is usually modulated by the orbital cycle of the system, which suggests that the physical conditions are also periodic and reproducible. The diversity of systems, together with the reproducibility of the conditions within each system, makes gamma-ray binaries excellent physical laboratories in which high energy particle acceleration, diffusion, absorption, and radiation mechanisms can be explored. Nevertheless, the number of known gamma-ray binaries is still very limited, and only a six binary systems have been classified as gamma-ray binaries. These systems produce outflows of relativistic particles emitting synchrotron radio emission that extend up to several astronomical units, which correspond to projected angular scales of a few milliarcseconds (mas) at typical distances of 2-3 kpc. Very Long Baseline Interferometry (VLBI) provide mas resolution and therefore can be used to directly see this radio outflow. In this thesis we present VLBI observations of five of the six gamma-ray binaries known. We have revealed for the first time the radio structure of two gamma-ray binaries, and found periodic changes in the structure of other two. Based on these results, we have established the basic properties and behaviour of the radio emission of gamma-ray binaries on AU scales, and we have contributed to find characteristics that are common to all of them.En los últimos años se ha producido una mejora significativa de los instrumentos que permiten observar fenómenos astrofísicos en rayos gamma de alta y muy alta energía. Gracias a estos avances, se ha podido detectar emisión de rayos gamma en sistemas binarios. Tan sólo seis sistemas binarios han sido clasificados como estrellas binarias de rayos gamma (tres de ellos aún son candidatos). Estos sistemas producen chorros de material relativista que a su vez producen grandes cantidades de energía en todo el espectro electromagnético, desde ondas radio hasta emisión de rayos gamma hasta energías del teraelectronvolt (TeV). Estos chorros se desplazan a alta velocidad produciendo estructuras en escalas de varias unidades astronómicas (UA). Estas estructuras pueden ser observadas directamente mediante técnicas de interferometría radio de muy larga línea de base (VLBI). En esta tesis nos centramos en el estudio de las propiedades morfológicas y astrométricas de binarias de rayos gamma observadas mediante VLBI. De las seis binarias conocidas, se han observado cinco de ellas. Los resultados principales son los siguientes. Se ha detectado estructura extendida en escalas de 120 UA en el sistema binario PSR B1259-63. Esta ha sido la primera evidencia observacional de que púlsares jóvenes no acretantes interaccionando con estrellas jóvenes pueden producir emisión radio extendida. Se ha descubierto que la emisión del sistema LS 5039 muestra cambios periódicos en su morfología, que son estables en escalas de varios años. También se ha determinado el movimiento propio de este sistema y se ha obtenido su trayectoria galáctica en el pasado. Se ha confirmado que el sistema LS I +61 303 muestra variabilidad orbital periódica, aunque presenta cambios significativos en ciertas fases orbitales. Se ha encontrado un desplazamiento del pico de la emisión a varias frecuencias, así como un cambio en sus posiciones relativas. Se ha descubierto emisión extendida procedente de la fuente de rayos gamma HESS J0632+057, y se ha confirmado inequívocamente su asociación con el sistema binario MWC 148. Por último, no se ha encontrado contrapartida radio a la fuente de rayos gamma AGL 2241+4454, cuya contrapartida óptica ha sido propuesta en el sistema MWC 656. Estos resultados permiten sentar las bases de la estructura en escalas de varias UA de los sistemas binarios de rayos gamma, así como su comportamiento en función de la fase orbital. Las características comunes halladas en estos sistemas ha permitido encontrar enlaces observacionales entre estos sistemas, dando consistencia a este particular grupo de estrellas que presentan emisión en rayos gamma.
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Hewitt, Danté Michael. "MeerKAT observations of novalike cataclysmic variables." Master's thesis, Faculty of Science, 2020. http://hdl.handle.net/11427/32726.
Full textAbstract:
I have conducted a systematic survey of eleven nearby novalike cataclysmic variables in the radio band, using the MeerKAT radio interferometer. Radio emission is detected from four out of the eleven systems: IM Eri, RW Sex, V3885 Sgr and V603 Aql. While RW Sex, V3885 Sgr and V603 Aql had been previously detected, this is the first reported radio detection of IM Eri. These observations have doubled the sample of non-magnetic cataclysmic varaibles with sensitive radio data. I observe that at these radio detection limits, a specific optical luminosity & 2.2 × 1018 erg s−1 Hz−1 (corresponding to MV . 6.0) is required to produce a radio detection. I also find that the X-ray and radio luminosities of the detected novalikes are on an extension of the LX ∝ L ∼0.7 R power law originally proposed for non-pulsating neutron star low-mass X-ray binaries. No other correlations are found between the radio emission and emission in other wavebands or any other system parameters for the existing sample of radio-detected novalikes. In-band (0.9–1.7 GHz) radio spectral indices are measured, and are found to be consistent with reports from earlier work. I construct broad spectral energy distributions for this sample from published multi-wavelength data, and use them to place constraints on the mass transfer rates of these eleven systems. Finally, I also present the results of time-resolved optical spectroscopy of two little-studied systems in the sample: V5662 Sgr and LSIV -08 3. I obtain orbital periods for these two systems that are consistent with previous measurements in the literature.
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Stevens, Jason Anthony. "Multifrequency observations of blazars." Thesis, University of Central Lancashire, 1995. http://clok.uclan.ac.uk/20140/.
Full textAbstract:
Blazars are a class of active galactic nuclei (AGN). Active galaxies are those that host compact sources of non-thermal radiation in their nuclear regions and are usually classified as being radio-loud or radio-quiet. The nature of the central source is ullcertain, but arguments based on energy budget suggest that accretion onto a supermassive black hole is the most probable scenario (Rees 1984). At present, there is no satisfactory theory that can explain the difference between radio-loud and radio-quiet AGN. The emission from radio-quiet AGN is regarded as being thermal in origin. Thermal re-radiation of the nuclear energy by dust in the host galaxy is thought to be an important process in these sources (Bregman 1990; Hughes et al. 1993). Radio-loud sources are dominated by non-thermal radiation which is almost certainly synchrotron in origin. Blazars are the most extreme example of radio-loud AGN and as such, provide the best opportunity to investigate further the emission mechanisms associated with radio-loudness. The term blazar (Angel & Stockman 1980) was originally applied to two groups of AGN which exhibit similar properties, namely BL Lacertae objects and optically violently variable (OVV) quasars. The BL Lac objects can be further split into radio selected BL Lac objects (RBLs) and X-ray selected BL Lac objects (XBLs). The difference between these two groups may only be due to the angleat which the jet (see below) is directed towards the line-of-sight of the observer. In this scenario the RBLs are more closely aligned (e.g. Gear 1994). The BL Lac objects studied in this work are all RBLs. In recent years, differences between OVV quasars and BL Lac objects have become apparent and these, together with the similarities that led to the original unification, will be discussed below. It is now more correct to assign the term blazar to a phenomenon rather than to a distinct class of AGN.
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Baubock, Michael, and Michael Baubock. "Effects of Spin on Neutron-Star Observations." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621065.
Full textAbstract:
Measurements of neutron-star properties provide a natural way to test models of cold dense matter and theories of gravity. In order to correctly interpret these measurements, accurate models taking into account the special and general relativistic effects arising from the strong gravity and fast spin of these sources are necessary. Moreover, for some observables the effects of the rapid spin can dominate the measurement. In this thesis, I develop a ray-tracing algorithm using the Hartle-Thorne metric that allows me to determine the effects of gravity on several observables. I use this algorithm to calculate the bias introduced when observations are interpreted under the common assumption that the source is slowly spinning or not spinning at all. I show that this assumption can lead to errors in mass and radius measurements that are larger than the accuracy needed to distinguish between different models for the equation of state.