Dissertations / Theses on the topic 'Stellar astronomy and planetary systems'
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Soto, Vásquez Maritza Gabriela. "Detection and characterization of single and double stellar/planetary systems." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/159571.
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Doctora en Ciencias, Mención AstronomíaEl crecimiento exponencial del número de exoplanetas descubiertos en los últimos años ha derivado en un mayor entendimiento de los planetas en la galaxia, de los cuales la Tierra es miembro; pero aún nos queda un gran camino por delante. El propósito de esta tesis es descubrir y confirmar nuevos planetas orbitando estrellas enanas y gigantes, además de desarrollar técnicas para extraer la mayor cantidad de información posible de las estrellas, permitiendo así una mayor compresión de los sistemas planetarios en estudio. Primero, analizamos datos crudos tomados con FEROS de las estrellas HD 11977, HD 47536, HD 110014, y HD122430, todas con al menos un planeta descubierto. Confirmamos la existencia de los planetas orbitando a HD 11977, HD 47536 y HD 110012, pero con parámetros orbitales distintos a los publicados. Además, no encontramos evidencia que respaldara la existencia del segundo planeta orbitando a HD 47536, ni que hubiese planetas alrededor de HD 122430 y HD 70573. Finalmente, reportamos el descubrimiento de un segundo planeta orbitanto a HD 110014, con una masa mínima de 3.1 \mjup y periodo orbital de 130 días. Luego, usando datos fotométricos de la campaña 11 y 12 de la misión K2, junto con mediciones de velocidad radial tomados con los espectrógrafos HARPS, FEROS, y Coralie, reportamos el descubrimiento de dos planetas Jupiter calientes orbitando a dos estrellas enanas. Encontramos que K2-237 b y K2-238 b tienen masas de $1.36^{+0.10}_{-0.10}$ y $0.86^{+0.13}_{-0.12}$ \mjup, radio de $1.63^{+0.07}_{-0.08}$ y $1.30^{+0.15}_{-0.14}$ \rjup, y orbitan a sus estrellas con órbitas de 1.28 y 3.2 días, respectivamente. El gran tamaño de K2-237 b nos lleva a concluir que corresponde a un Jupiter caliente altamente inflado, mientras que el radio de K2-238 b es consistente con modelos teóricos. K2-237 b representa un excelente laboratorio para estudios de atmósferas planetarias. Finalmente, desarrollamos una herramiento que permite el cálculo automático de parámetros estelares para grandes cantidades de estrellas, usando espectros echelle de alta resolución. SPECIES mide anchos equivalentes para un gran número de líneas de fierro y los usa para resolver la ecuación de transferencia radiativa asumiento equilibrio termodinámico local para obtener los párametros atmosféricos. Estos valores son usados para obtener la abundancia de 11 elementos químicos en las atmósferas estelares. La velocidad de rotación y de macroturbulencia son obtenidos usando fórmulas calibradas a la temperatura estelar, y perfiles de línea sintéticos que igualen a los perfiles medidos para cinco líneas de absorción. SPECIES obtiene la masa, radio y edad interpolando en isocronas MIST, usando el método Bayesiano. Luego de una serie de pruebas encontramos que los parámetros que obtiene SPECIES son congruentes con los de la literatura. También derivamos relaciones analíticas que describen las correlaciones entre los parámetros, e implementamos nuevos métodos para trabajar con estas correlaciones en la obtención de las incertezas asociadas a cada medición.
Este trabajo ha sido parcialmente financiado por CONICYT-PCHA/Doctorado Nacional/2014-21141037
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Burke, Christopher J. "Survey for transiting extrasolar planets in stellar systems stellar and planetary content of the Open Cluster NGC 1245 /." Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1132168623.
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Schröter, Sebastian [Verfasser], and Jürgen H. M. M. [Akademischer Betreuer] Schmitt. "Analysis of Stellar Activity and Orbital Dynamics in Extrasolar Planetary Systems / Sebastian Schröter. Betreuer: Jürgen H. M. M. Schmitt." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2012. http://d-nb.info/1024355306/34.
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Bruno, Giovanni. "Characterization of transiting exoplanets : analyzing the impact of the host star on the planet parameters." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4746/document.
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Dans le cadre de ma thèse, j’ai analysé les spectres de neuf étoiles Kepler obtenus avec les relevés de vitesse radiale (VR). Cela a permis la caractérisation de leur compagnons planétaires. J’ai analysé les spectres de 21 autres étoiles CoRoT et Kepler, probablement hôtes de naines M à faible masse. Cela a permis d’'élargir l'échantillon des étoiles à faible masse avec masse et rayon mesurés. J’ai calculé l’indice d’activité chromosphérique de 31 étoiles observées avec SOPHIE/OHP, en aidant l’étude des interactions étoile-planète. J’ai étudié le comportement de SOPHIE à bas signal à bruit (S/B). J’ai déterminé l’intervalle de S/B dans lequel un spectre stellaire est fiable pour la mesure des paramètres stellaires.Dans le cadre du consortium SOPHIE, j’ai suivi l’analyse complète du système Kepler-117. Ce système multi-planétaire montre variations des périodes orbitaux dues aux échanges dynamiques entre les planètes (TTV). Pour déterminer les paramètres du système, un approche spécifique a été développé pour l’ajustement simultané de transits, VR et TTV (Bruno et al. 2015).Finalement, je me suis intéressé à l’activité stellaire dans la photométrie de transit. J’ai impl ́ementé deux logiciels de modélisation de tâches stellaires dans un code MCMC, en ajoutant l’évolution des tâches dans l’un d’eux. J’ai appliqué les logiciels au Soleil, à CoRoT-7 et à CoRoT-2. J’ai amené un étude détaillé de la courbe de lumière de CoRoT-2, et exploré les effets des tâches dans les paramètres du transit (Bruno et al., en prep.). Avec la méthode FF’ (Aigrain et al. 2012), j’ai contribué à l’exploration du lien entre la signature des tâches de CoRoT-7 et dans la photométrie et dans les VRDuring my PhD, I analyzed the spectra of nine Kepler stars obtained by radial velocity (RV) observations. This allowed the characterization of their planetary companions. I analyzed the spectra of twenty-one other CoRoT and Kepler stars, likely orbited by low-mass M dwarfs. This helped widening the sample of low-mass stars with measured mass and radius. I calculated the chromospheric activity indfex of thirty-one stars observed with SOPHIE/OHP, helping the study of star-planet interactions. I studied the behavior of SOPHIE in low signal-to-noise ratio (SNR) regime. I determinhed the SNR range in which a stellar spectrum is reliable for the measure of the stellar parameters.Within the SOPHIE consortium, I followed the complete analysis of the Kepler-117 system. This multi-planetary system presents variations in the planetary orbital periods due to their mutual dynamical interacion (TTVs). To fit the system parameters, a specific fitting approach including TTV modeling was developed. We derived the system parameters by the simultaneous fit of transits, RVs, and TTVs (Bruno et al. 2015).Finally, I addressed the problem of stellar activity in transit photometry. I implemented two starspot modeling codes into an MCMC algorithm, adding spot evolution to oneof them. I applied the codes to the Sun, CoRoT-7, and CoRoT-2. I carried an extensive study on the light curve of CoRoT-2, and explored the effects of the spots on the transit parameters (Bruno et al., in prep.). With the FF’ method (Aigrain et al. 2012), I contributed to explore the connection between the photometric and RV signature of starspots in CoRoT-7
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Fusillo, Nicola P. G. "Stellar and planetary remnants in large area surveys." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/77318/.
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The advent of large-area digital sky surveys marked a turning point for the entire field of astronomy. Today, with multi-band photometry for hundreds of millions of objects readily at hand, the ability to mine data for specific rare objects of interest has become of fundamental importance. The aim of this work was to study white dwarfs and planetary remnants by, first of all, developing efficient selection algorithms to identify these objects in large area surveys. Using SDSS DR7 we developed a routine which relies on colours and proper motion to calculate probabilities of being a white dwarf (PWD) which, in turn, enables a flexible selection of white dwarf candidates without recourse to spectroscopy. The application of this selection method to SDSS DR10 lead to the creation of a catalogue of ≃ 66, 000 bright (g ≤ 19) objects with calculated PWD from which it is possible to select ≃ 23, 000 high-confidence white dwarf candidates . The reliability of the method was further tested using a sample of spectroscopic objects from the LAMOST survey. This independent test confirmed the robustness of our algorithm and lead to the identification of 290 new white dwarfs. We also applied our selection routine to the recently released ATLAS DR2 to construct a preliminary catalogue of ≃ 9000 ATLAS white dwarf candidates. This catalogue represents the first sample of white dwarfs candidates in the southern hemisphere. We later exploited our catalogue in several science project. We developed a separate selection algorithm to identify variable white dwarfs in large area time-domain surveys. To test this method we carried out a pilot search for pulsating white dwarfs using 400 high-confidence white dwarfs candidates with available multi-epoch photometry in SDSS Stripe 82. This test proved the ability of our method to select different types of variable white dwarfs and allowed to identify 5 pulsating white dwarfs, 3 of which are new discoveries. During the development of our catalogue, we also identified 64 new metal polluted white dwarfs. Recent studies have shown that the metal pollution in these objects is the result of accretion of remnants of planetary systems. In a few cases these planetary remnants form a circustellar debris disc which can be detected as an infrared excess. Here we present the results of high-resolution spectroscopic follow-up of 15 of the newly identified metalpolluted white dwarfs. Using accurate spectral analyses of the atmospheres of these white dwarfs we determined chemical compositions and masses of the accreted bodies, and discuss the impact of these finding on the current knowledge of extra-solar planetary systems. Using optical and infrared photometric data from various large-area surveys we carried out a search for infrared excess around our newly identified metal polluted white dwarfs, and high-confidence white dwarf candidates. We identified four metal polluted white dwarfs with possible debris discs and compiled a list of ≃ 300 white dwarfs candidates with infrared excess ready for future spectroscopic follow-up.
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Girven, Jonathan. "Stellar and planetary remnants in digital sky surveys." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/53749/.
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Large scale digital sky surveys have produced an unprecedented volume of uniform data covering both vast proportions of the sky and a wide range of wavelength, from the ultraviolet to the near-infrared. The challenge facing astronomers today is how to use this multitude of information to extract trends, outliers and and rare objects. For example, a large sample of single white dwarf stars has the potential to probe the Galaxy through the luminosity function. The aim of this work was to study stellar and planetary remnants in these surveys. In the last few decades, it has been shown that a handful of white dwarfs have remnants of planetary systems around them, in the form of a dusty disc. These are currently providing the best constraints on the composition of extra-solar planetary systems. Finding significant numbers of dusty discs is only possible in large scale digital sky surveys. I ultilised the SDSS DR7 and colour-colour diagrams to and DA white dwarfs from optical photometry. This nearly doubled the number of spectroscopically con- armed DA white dwarfs in the SDSS compared with DR4 [Eisenstein et al., 2006], and introduced nearly 10; 000 photometric-only DA white dwarf candidates. I further cross-matched our white dwarf catalogue with UKIDSS LAS DR8 to carry out the currently largest and deepest untargeted search for low-mass companions to, and dust discs around, DA white dwarfs. Simultaneously, I analyzed Spitzer observations of 15 white dwarfs with metal-polluted atmospheres, all but one having helium-dominated atmospheres. Three of these stars were found to have an infrared excess consistent with a dusty disc. I used the total sample to estimate a typical disc lifetime of log[tdisc(yr)] = 5:6+1:1, which is compatible with the relatively large range estimated from different theoretical models. Subdwarf population synthesis models predicted a vast population of subdwarfs with F to K-type companions, produced in the effcient RLOF formation channel. I used a cross-match of ultraviolet, optical and infrared surveys to search for this unseen population. I select a complementary sample to those found from radial velocity surveys, offering direct tests of binary evolution pathways. Finally, I present a method to use common proper motion white dwarf pairs to constrain the initial-final mass relation, which is extremely uncertain at low masses. In the example I show, one of the stars is a magnetic white dwarf with B ' 6 MG, making this a rare and intriguing system from a magnetic white dwarf formation point of view.
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Savino, A. "On the complex stellar populations of ancient stellar systems." Thesis, Liverpool John Moores University, 2018. http://researchonline.ljmu.ac.uk/9190/.
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The study of ancient stellar systems in the vicinity of the Milky Way provides a wealth of information on the conditions, in the early Universe, that led to the properties we observe today in galaxies and in their constituent components. Resolved stellar populations enable us to gain detailed insights on the age and chemical composition of such stellar systems, tracing their properties on a fine spatial scale. The deep investigation of Local Group objects revealed that even very old, low mass, stellar systems host unexpected complexities in their stellar populations. Such complexities remain largely unexplained, our understanding limited by observational and theoretical limitations. Here I present work aimed at a deeper characterisation of the complex stellar popula- tions in dwarf spheroidal galaxies and Galactic globular clusters. I use a combination of observational and modelling techniques to shed light on the detailed stellar properties of these objects. Part of my investigation focuses on the horizontal branch of dwarf spheroidal galaxies. By careful modelling of the horizontal branch in the galaxy Carina, which has well known star formation history, I demonstrate that the horizontal branch contains precious information, that can be used to refine age measurements in nearby galaxies. To this aim, I develop a new modelling method that, for the first time, combines constraints from the main sequence turn-off and the horizontal branch to provide very precise measurements of the star formation history in resolved galaxies. The combined information from different regions of the colour-magnitude diagram permits to recover the value of mass loss experienced by red giant branch stars with very high precision. I test this technique on a range of synthetic populations and on the well studied galaxy Sculptor, demonstrating the increased age resolution that this approach provides. I apply my modelling tool to the distant galaxy Tucana, determining a very detailed star formation history, where multiple events of star formation can be clearly distinguished. The identification of the different stellar populations on the horizontal branch permits us to characterise the spatial distribution of the star formation events in this galaxy. I also perform a photometric study of the massive globular cluster M13, focussing on the multiple stellar populations present in this object. I identify and trace the different stellar populations out to most external regions of this cluster. The spatial distribution of these populations, which shows no sign of radial segregation, reveal the very advanced dynamical evolutionary stage of the cluster. The work presented in this manuscript constitutes a step forward to understand the formation of low mass ancient stellar systems and paves the way for deeper studies of large samples of stellar systems in the Milky Way vicinity.
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McLean, William George King. "Polarimetry of planetary systems." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/98039/.
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Light reflected by planetary atmospheres and/or surfaces is polarised, and the degree and direction of polarisation can yield information that cannot always be gleaned from flux measurements alone. Polarimetric studies of solar system planets can reveal more details about the seasonal variations in their atmospheres, and the variation with orbital geometry can place constraints on the properties of cloud particles. With the advent of extremely large telescopes, and potentially the most accurate instruments ever realised thus far, polarimetry has great potential for both detecting and characterising exoplanets. A key difference when observing exoplanets with respect to the planets of our solar system is that despite the much lower signal-to-noise than solar system planets, we can access them at wider phase angle ranges, thus enabling us to probe their scattering properties more extensively, especially at geometries where the degree of polarisation is highest. This can result in an easier interpretation of the atmospheric characteristics through theoretical modelling. My original contribution to the field that is presented in this thesis is the observation, data reduction and analysis of polarimetric data along with model interpretation of the six most outer solar system planets and Titan. In addition, model results for exoplanets of varying types are shown and discussed. The overall goal is to show that polarimetry is necessary for giving a full description of light reflected by planetary atmospheres and surfaces, and to demonstrate its worth as a diagnostic tool for atmospheric characterisation, from both ground-based observations of solar system and exoplanets, and from in-situ missions to the outer planets, such as a potential atmospheric probe into any of the outer planets.
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Nelson, Katy. "On the origin of the stellar initial mass function and multiple stellar systems." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/65971/.
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I first perform a statistical analysis on a distribution of pre-stellar core masses. Each core is split into a small number of stars, and two stars are chosen using a prescription based on stellar masses to form a binary system. The rest of the stars are taken to be singles. From this sample of binaries and singles, I compute the stellar initial mass function, the binary frequency and mass ratio distribution as a function of primary mass. I then test if the observed binary frequencies and mass ratios are compatible with this self-similar mapping of cores into stars. I show that self-similar mapping can reproduce the observed binary frequencies and mass ratios well, so long as the efficiency is rather high (100%), and each core fragments into about 4 or 5 stars. Using the code Seren view, I then perform N-body simulations with core-clusters. I investigate the formation of multiple systems, and qualify the dependence of their parameters and longevity on certain initial conditions, including (i) the number of stars in a core-cluster, (ii) the variance of masses in those stars, (iii) the virial ratio and (iv) radial dependence of stellar density. I expand on those results by including (a) a prescription for the influence of disks during stellar ybys, (b) different initial spatial configurations of the stars (i.e. line and ring clusters) and (c) a background potential due to residual gas in the core-cluster. The full range of periods observed in the field cannot be explained by the distribution of periods of pure binaries alone, which is too narrow. However, the wide range can be explained either by combining the periods of pair-wise orbits of all multiple systems, i.e. the widest periods observed are in fact pair-wise orbits of higher-order multiples with unresolved companions, or by considering a distribution of pre-stellar cores that have a range of virial ratios.
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Skemer, Andrew. "HIGH SPATIAL RESOLUTION MID-INFRARED STUDIES OF PLANETARY SYSTEMS." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202978.
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I present the results of six papers related the formation and evolution of planets and planetary systems, all of which are based on high-resolution, ground-based, mid-infrared observations.The first three chapters are studies of T Tauri binaries. T Tauri stars are young, low mass stars, whose disks form the building blocks of extrasolar planets. The first chapter is a study of the 0.68"/0.12" triple system, T Tauri. Our spatially resolved N-band photometry reveals silicate absorption towards one component, T Tau Sa, indicating the presence of an edge-on disk, which is in contrast to the other components. The second chapter is an adaptive optics fed N-band spectroscopy study of the 0.88" binary, UY Aur. We find that the dust grains around UY Aur A are ISM-like, while the mineralogy of the dust around UY Aur B is more uncertain, due to self-extinction. The third chapter presents a survey of spatially resolved silicate spectroscopy for nine T Tauri binaries. We find with 90\%-95\% confidence that the silicate features of the binaries are more similar than those of randomly paired single stars. This implies that a shared binary property, such as age or composition, is an important parameter in dust grain evolution.The fourth chapter is a study of the planetary system, 2MASS 1207. We explore the source of 2MASS 1207 b's under-luminosity, which has typically been explained as the result of an edge-on disk of large, grey-extincting dust grains. We find that the edge-on disk theory is incompatible with several lines of evidence, and suggest that 2MASS 1207 b's appearance can be explained by a thick cloudy atmosphere, which might be typical among young, planetary systems.The fifth chapter is a study of the white dwarf, Sirius B, which in the context of this thesis is being studied as a post-planetary system. Our N-band imaging demonstrates that Sirius B does not have an infrared excess, in contrast to previous results.The sixth chapter is a study of mid-infrared atmospheric dispersion, which in the context of this thesis is being studied as an effect that will limit the ability of ELTs to image planetary systems. We measure mid-infrared atmospheric dispersion, for the first time, and use our results to confirm theoretical models.
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Stergiopoulou, Aikaterini. "Dynamical Stability of Planetary Systems." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-323006.
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The study of dynamical stability in planetary systems has become possible during the last few decades due to the development of numerical methods for long-term integrations of N-body systems. Since the 90’s the number of exoplanet detections has been increased significantly, making the simulations of other real planetary systems besides the Solar System feasible. One of the exciting new-found worlds is the system Kepler-11. Six planets which are located very close to each other orbit a solar-type star. In this project we first investigate the behavior of Kepler-11 when we change some of the initial conditions of the outermost planet of the system and then we approximate the Red Giant phase of solar-type stars in order to see how the planetary orbits are altered. For the first part we run three series of simulations (groups A,B,C). Each group has a different value for the mean density of planet Kepler-11g (1.0,1.5,2.0 g/cm 3 ). We run simulations for 36 different combinations of mass and eccentricity of planet Kepler-11g for each group. In nine configurations all six planets of the system continue to orbit the star until the end of the simulations. These nine stable configurations of Kepler-11 are used in the second part where we implement a constant mass-loss rate for the star which results in 30% mass loss after 30 million years, trying to approximate that way the mass loss of solar-type stars in Red Giant Branch. We also run nine simulations of a hypothetical system consisting only of the Sun, Earth and Jupiter where we implement the constant mass-loss rate to the Sun. In the Kepler-11 system, the orbits of planets Kepler-11g and Kepler-11e change by ∼45% and ∼54% respectively, after 30 million years, due to the mass loss of the star, while in the hypothetical planetary system the orbits of the two planets change by ∼43%. The study of orbits and how they move outward during the Post-Main Sequence evolution of stars is essential for our understanding of the existence of a Habitable Zone, not just around stars in Main-Sequence phase, but also around stars in late stages of their evolution.
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Bailey, Vanessa Perry. "Adaptive Optics for Directly Imaging Planetary Systems." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/577514.
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In this dissertation I present the results from five papers (including one in preparation) on giant planets, brown dwarfs, and their environments, as well as on the commissioning and optimization of the Adaptive Optics system for the Large Binocular Telescope Interferometer. The first three Chapters cover direct imaging results on several distantly-orbiting planets and brown dwarf companions. The boundary between giant planets and brown dwarf companions in wide orbits is a blurry one. In Chapter 2, I use 3–5 μm imaging of several brown dwarf companions, combined with mid-infrared photometry for each system to constrain the circum-substellar disks around the brown dwarfs. I then use this information to discuss limits on scattering events versus in situ formation. In Chapters 3 and 4, I present results from an adaptive optics imaging survey for giant planets, where the target stars were selected based on the properties of their circumstellar debris disks. Specifically, we targeted systems with debris disks whose SEDs indicated gaps, clearings, or truncations; these features may possibly be sculpted by planets. I discuss in detail one planet-mass companion discovered as part of this survey, HD 106906 b. At a projected separation of 650 AU and weighing in at 11 Jupiter masses, a companion such as this is not a common outcome of any planet or binary star formation model. In the remaining three Chapters, I discuss pre-commissioning, on-sky results, and planned work on the Large Binocular Telescope Interferometer Adaptive Optics system. Before construction of the LBT AO system was complete, I tested a prototype of LBTI's pyramid wavefront sensor unit at the MMT with synthetically-generated calibration files. I present the methodology and MMT on-sky tests in Chapter 5. In Chapter 6, I present the commissioned performance of LBTIAO. Optical imperfections within LBTI limited the quality of the science images, and I describe a simple method to use the adaptive optics system to correct for the science camera's optical aberrations. Finally, in Chapter 7, I discuss the status of a more sophisticated method for correcting these optical aberrations in LBTI.
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Tabera, Martin Luis. "Evolution and properties of planetary systems." Thesis, Uppsala universitet, Observationell astrofysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-438128.
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Wilson, David John. "Observations of remnant planetary systems at white dwarfs." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/101779/.
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The detection of remnant planetary systems at white dwarfs allows the end stages of planetary evolution to be explored observationally. This thesis presents observations of white dwarfs and describes the contributions they make to planetary science. Firstly, white dwarf science probes the end states of the majority of known planetary systems, including the Solar system. In Chapter 3 I present the discovery of strongly variable emission lines from gas in a debris disc around the white dwarf SDSS J1617+1620. Time-series spectroscopy obtained during the period 2006–2014 has shown the appearance and then complete disappearance of strong double-peaked Ca ii emission lines. These observations represent unambiguous evidence for short-term variability in the debris environment of evolved planetary systems. Possible explanations for this extraordinary variability include the impact onto the debris disc of a single small rocky planetesimal, or interactions between material in a highly eccentric debris tail. I also use observations of white dwarfs to contribute to exoplanet science more generally. Metal pollution from planetary debris is visible in spectra of white dwarfs, providing the only technique to directly measure the bulk chemical composition of rocky extrasolar material. Chapter 4 presents a detailed study of the metal-polluted white dwarf SDSS J0845+2257, using high-resolution HST/COS and VLT spectroscopy to detect hydrogen and eleven metals originating in an orbiting debris disc. The chemistry of the debris is broadly similar to the Earth, but enhanced abundances of core material (Fe, Ni) suggest that the planetesimal from which the debris formed may have lost a portion of its mantle. Conversely, in Chapter 5 I focus on the detection of just carbon and oxygen, but at 16 different white dwarfs to search for hypothetical “carbon planets”. I find no evidence for carbon-rich planetesimals, with C/O< 0:8 by number in all 16 systems. I place an upper limit on the occurrence of carbon-rich systems at < 17 percent. The range of C/O of the planetesimals is consistent with that found in the Solar System. White dwarfs can also be fascinating objects in their own right. In Chapter 6 I present HST observations of the mysterious white dwarf GD 394, a hot, extremely metal polluted white dwarf. Extreme ultraviolet observations in the mid 90s revealed a 1.15 day periodicity with a 25 per cent amplitude, hypothesised to be due to a surface accretion spot. I obtained phase-resolved HST/STIS high-resolution FUV spectra of GD 394 that sample the entire period, along with a large body of supplementary data. I use these data to test the hypothesis of an accretion spot, search for variability in accretion rates over decades-long timescales, and probe the immediate circumstellar environment of GD 394.
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COOK, KEM HOLLAND. "ASYMPTOTIC GIANT BRANCH POPULATIONS IN COMPOSITE STELLAR SYSTEMS." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184208.
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This dissertation presents a technique for the identification and classification of late-type stars and for the estimation of M star metallicities. The technique uses broad-band, V and I, CCD images to identify red stars and two intermediate-band CCD images to classify these as carbon or M types. One of the intermediate passbands is centered on a TiO absorption band at 7750Å and the other is centered on a CN absorption band at 8100Å. Color-color plots of V-I versus the intermediate-band index, 77-81, clearly distinguishes carbon from M stars. Observations of both early- and late-type stars were used to define the 77-81 system based upon the intermediate-band filters. The TiO bandstrength deduced from the 77-81 color as a function of V-I color was investigated for field giants and giants in 12 globular clusters. A linear correlation between [Fe/H] and the V-I color at a given TiO bandstrength was found. This correlation can be used to estimate the metallicity of M giants. The stellar population of a field in Baade's Window was examined using this technique. Many late-M stars and no carbon stars were found. The color-color diagram for Baade's Window suggests a range of metallicities for the M giants of [Fe/H] ≈ -0.4 to > +0.2. The stellar population of the Sagittarius Dwarf Irregular galaxy (Sagdig) was examined using the 77-81 system. A method for estimating reddening based upon the color mode of foreground stars was developed for the analysis of the Sagdig data. Sagdig is estimated to be ~ 1.3 megaparsecs distant. Bright blue and red stars in Sagdig are evidence for recent star formation. Carbon stars were identified in Sagdig. They display a bimodal luminosity and color distribution which suggests distinct epochs of star forming activity between 1 and 10 Gyr ago. The spatial distribution of carbon stars and bright red stars in Sagdig shows this galaxy to be much larger than previously thought.
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Eatchel, Andrew L. "Imaging exo-solar planetary systems with Terrestrial Planet Finder." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280604.
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The concept of building a space based telescope capable of directly imaging extra-solar planetary systems has been in existence for more than a decade. While the basic ideas of how such an instrument might work have already been discussed in the literature, specific details of the design have not been addressed that will enable a telescope of this class to be functionally realized. A straw man configuration of the instrument is examined here for its ability to acquire data of sufficient informational content and quality to produce images and spectra of distant planetary systems and to find what technical problems arise from analyzing the interferograms it delivers. Computer programs that simulate the signals expected to be produced by a structurally connected instrument (SCI) version of Terrestrial Planet Finder (TPF) and reconstruct images from those signals will be presented along with programs that extract planetary parameters. An abbreviated radiometric performance analysis will also be provided that will assist astronomers in designing an appropriate mission.
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Dawson, Rebekah Ilene. "On the Migratory Behavior of Planetary Systems." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10955.
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For centuries, an orderly view of planetary system architectures dominated the discourse on planetary systems. However, there is growing evidence that many planetary systems underwent a period of upheaval, during which giant planets "migrated" from where they formed. This thesis addresses a question key to understanding how planetary systems evolve: is planetary migration typically a smooth, disk-driven process or a violent process involving strong multi-body gravitational interactions? First, we analyze evidence from the dynamical structure of debris disks dynamically sculpted during planets' migration. Based on the orbital properties our own solar system's Kuiper belt, we deduce that Neptune likely underwent both planet-planet scattering and smooth migration caused by interactions with leftover planetesimals. In another planetary system, Beta Pictoris, we find that the giant planet discovered there must be responsible for the observed warp of the system's debris belt, reconciling observations that suggested otherwise. Second, we develop two new approaches for characterizing planetary orbits: one for distinguishing the signal of a planet's orbit from aliases, spurious signals caused by gaps in the time sampling of the data, and another to measure the eccentricity of a planet's orbit from transit photometry, "the photoeccentric effect." We use the photoeccentric effect to determine whether any of the giant planets discovered by the Kepler Mission are currently undergoing planetary migration on highly elliptical orbits. We find a lack of such "super-eccentric" Jupiters, allowing us to place an upper limit on the fraction of hot Jupiters created by the stellar binary Kozai mechanism. Finally, we find new correlations between the orbital properties of planets and the metallicity of their host stars. Planets orbiting metal-rich stars show signatures of strong planet-planet gravitational interactions, while those orbiting metal-poor stars do not. Taken together, the results of thesis suggest that suggest that both disk migration and planet-planet interactions likely play a role in setting the architectures of planetary systems.Astronomy
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Hinz, Philip Mark. "Nulling interferometry for studying other planetary systems: Techniques and observations." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/280541.
Full textAbstract:
Nulling interferometry is an important technique in the quest for direct detection of extrasolar planets. It is central to NASA's plans for a Terrestrial Planet Finder (TPF) mission to detect and characterize Earth-like planets. This thesis presents the first experiments to demonstrate that the technique is a useful tool for ground-based observations as well. It demonstrates the ability of the technique to study faint, circumstellar environments otherwise not easily observed. In addition the observations and experiments allow more confident estimation of expected sensitivity to planetary systems around nearby stars. The old MMT was used for the first telescope experiments of stellar suppression via nulling. The stellar suppression achieved was sufficient to observe thermal emission from cool dust in the outflows around late-type stars. Based on the original MMT prototype, which worked at ambient temperature, I have constructed a cryogenic nulling interferometer for use with the renovated 6.5 m MMT. Features include the capability of sensing and correcting the phase between the two arms of the interferometer, achromatic tuning of the null using a unique symmetric beam-splitter, and compatibility with the deformable secondary of the MMT. The instrument has been used in a laboratory setup with an artificial source to demonstrate a high level of suppression. Commissioning of the instrument took place at the MMT in June 2000 using the fixed f/9 secondary. The instrument was aligned, phased, and used for science observations of 17 stars over five nights. The future impact of nulling with the MMT and the Large Binocular Telescope is sketched out. These telescopes will be sensitive to very faint levels of zodiacal dust, indicative of planetary companions and giving us clues as to the make up of planetary systems. Substellar companions down to near Jupiter mass will be detectable around the nearest stars for the LBT, allowing direct imaging of long-period giant planets. The detection of such companions will be complementary to the Doppler velocity searches, currently so successful in verifying the existence of planets, thus giving a balanced view of the prevalence and range of separations possible for giant planets around nearby stars.
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Neilson, Hilding R., Joseph T. McNeil, Richard Ignace, and John B. Lester. "Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-darkening Directly from Model Stellar Atmospheres." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2684.
Full textAbstract:
The transit method, employed by Microvariability and Oscillation of Stars (MOST), Kepler, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, starspots, and other phenomena at the level of a few hundred parts per million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived from stellar atmosphere models or fit directly. In this work, we revisit this assumption and compute synthetic planetary-transit light curves directly from model stellar atmosphere center-to-limb intensity variations (CLIVs) using the plane-parallel Atlas and spherically symmetric SAtlas codes. We compare these light curves to those constructed using best-fit limb-darkening parameterizations. We find that adopting parametric stellar limb-darkening laws leads to systematic differences from the more geometrically realistic model stellar atmosphere CLIV of about 50–100 ppm at the transit center and up to 300 ppm at ingress/egress. While these errors are small, they are systematic, and they appear to limit the precision necessary to measure secondary effects. Our results may also have a significant impact on transit spectra.
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Bradnick, Benjamin Thomas George. "On the dynamics in planetary systems, globular clusters and galactic nuclei." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7826/.
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N-body simulations are used to investigate the dynamics of planetary systems based on the observed period-radius distribution by Kepler. The stability of the distri- bution is tested using integrations of 2,000 systems and with the addition of a Jupiter-like perturber in an aligned and inclined configuration sufficient for Lidov- Kozai (LK) oscillations. ∼ 67% of planetary systems are found stable, falling to ∼ 62% and ∼ 48% with an aligned or inclined giant perturber. Planet ejections are rare. Instability timescales of systems are predicted by spacing and multiplicity of planets, but exceptions are common. Evolution of select individual systems are investigated and classified. The dynamics of stellar binaries on eccentric orbits around a massive black hole (MBH) in the empty loss cone (LC) are also explored. The LK mechanism is sup- pressed by two-body relaxation from stars in galactic nuclei whilst tidal perturba- tions from the MBH excite the eccentricity of the binary to produce mergers in ∼ 75% of simulations. Stellar tides circularise the binaries and produce low velocity mergers. Enhanced magnetic fields in merger products could explain relativistic jet formation in tidal disruption events (TDEs). A method is presented for rapidly calculating the stellar evolution of stars with masses \[m=8.0-300.0M_\odot\] and metallicities \[-4.0\leq [Z/H]\leq 0.5\] that can be incorporated into future n-body simulations.
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Martinez, Arturo O., Ian J. M. Crossfield, Joshua E. Schlieder, Courtney D. Dressing, Christian Obermeier, John Livingston, Simona Ciceri, et al. "Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623204.
Full textAbstract:
The NASA K2 mission uses photometry to find planets transiting stars of various types. M dwarfs are of high interest since they host more short-period planets than any other type of main-sequence star and transiting planets around M dwarfs have deeper transits compared to other main-sequence stars. In this paper, we present stellar parameters from K and M dwarfs hosting transiting planet candidates discovered by our team. Using the SOFI spectrograph on the European Southern Observatory's New Technology Telescope, we obtained R approximate to 1000 J-, H-, and K-band (0.95-2.52 mu m) spectra of 34 late-type K2 planet and candidate planet host systems and 12 bright K4-M5 dwarfs with interferometrically measured radii and effective temperatures. Out of our 34 late-type K2 targets, we identify 27 of these stars as M dwarfs. We measure equivalent widths of spectral features, derive calibration relations using stars with interferometric measurements, and estimate stellar radii, effective temperatures, masses, and luminosities for the K2 planet hosts. Our calibrations provide radii and temperatures with median uncertainties of 0.059 R-circle dot (16.09%) and 160 K (4.33%), respectively. We then reassess the radii and equilibrium temperatures of known and candidate planets based on our spectroscopically derived stellar parameters. Since a planet's radius and equilibrium temperature depend on the parameters of its host star, our study provides more precise planetary parameters for planets and candidates orbiting late-type stars observed with K2. We find a median planet radius and an equilibrium temperature of approximately 3 R-circle plus and 500 K, respectively, with several systems (K2-18b and K2-72e) receiving near-Earth-like levels of incident irradiation.
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Pascucci, I., L. Testi, G. J. Herczeg, F. Long, C. F. Manara, N. Hendler, G. D. Mulders, et al. "A STEEPER THAN LINEAR DISK MASS–STELLAR MASS SCALING RELATION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622163.
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The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887 mu m survey of the disk population around objects from similar to 2 to 0.03 M-circle dot in the nearby similar to 2 Myr old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887 mu m flux densities into dust disk masses, hereafter M-dust. We find that the M-dust-M* relation is steeper than linear and of the form M-dust proportional to (M*)(1.3-1.9), where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr old regions of Taurus, Lupus, and Chamaeleon. I share the same M-dust-M* relation, while the 10 Myr old Upper. Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.
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Rodigas, Timothy John. "High-Contrast Near-Infrared Studies of Planetary Systems and their Circumstellar Environments." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/306772.
Full textAbstract:
Planets are thought to form in circumstellar disks, leaving behind planetesimals that collide to produce dusty debris disks. Characterizing the architectures of planetary systems, along with the structures and compositions of debris disks, can therefore help answer questions about how planets form. In this thesis, I present the results of five papers (three published, two in preparation) concerning the properties of extrasolar planetary systems and their circumstellar environments. Chapters 2 and 3 are studies of radial velocity (RV) exoplanetary systems. For years astronomers have been puzzled about the large number of RV-detected planets that have eccentric orbits (e>0.1). In Chapter 2 I show that this problem can partially be explained by showing that two circular-orbit planets can masquerade as a single planet on an eccentric orbit. I use this finding to predict that planets with mildly eccentric orbits are the most likely to have massive companions on wide orbits, potentially detectable by future direct imaging observations. Chapter 3 presents such a direct imaging study of the 14 Her planetary system. I significantly constrain the phase space of the putative candidate 14 Her c and demonstrate the power of direct imaging/RV overlap. Chapters 4 and 5 are high-contrast 2-4 μm imaging studies of the edge-on debris disks around HD 15115 and HD 32297. HD 15115's color is found to be gray, implying large grains 1-10 μm in size reside in stable orbits in the disk. HD 32297's disk color is red from 1-4 μm. Cometary material (carbon, silicates, and porous water ice) are a good match at 1-2 μm but not at L'. Tholins, organic material that is found in outer solar system bodies, or small silicates can explain the disk's red color but not the short wavelength data. Chapter 6 presents a dynamical study of dust grains in the presence of massive planets. I show that the width of a debris disk increases proportionally with the mass of its shepherding planet. I then make predictions for the masses and orbits of putative planets in five well-known disks. In Chapter 7, I summarize and discuss plans for future research in the exoplanet field.
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Coleman, Gavin Arthur Leonard. "Exploring the architectures of planetary systems that form in thermally evolving viscous disc models." Thesis, Queen Mary, University of London, 2016. http://qmro.qmul.ac.uk/xmlui/handle/123456789/23105.
Full textAbstract:
The diversity in observed planets and planetary systems has raised the question of whether they can be explained by a single model of planet formation or whether multiple models are required. The work presented in this thesis aims to examine the oligarchic growth scenario, to determine whether the core accretion model, where planets form bottom-up, can recreate the observed diversity. I begin by exploring how changing model parameters such as disc mass and metallicity influence the types of planetary systems that emerge. I show that rapid inward migration leads to very few planets with masses mp > 10M⊕ surviving, with surviving planetary systems typically containing numerous low-mass planets. I examine what conditions are required for giant planets to form and survive migration, finding that for a planet similar to Jupiter to form and survive, it must form at an orbital radius rp > 10 au. In the second project in this thesis, I update the physical models before examining whether a broader range of parameters can produce planetary systems similar to those observed. I find that compact systems of low-mass planets form in simulations if there is sufficient solid material in the disc or if planetesimals are small, thus having increased mobility. I also find that giant planets can form when the solid abundance and mobility of planetesimals are high, however they all undergo largescale migration into the magnetospheric cavity located close to the star. For the final project of this thesis, I examined the effects that disc radial structuring has on the formation of giant planets. I find that by including radial structures, numerous giant planets are able to form at large orbital radii and survive migration. The observed period valley between 10-100 days is also recreated, of which I attribute to disc dispersal late in the disc's lifetime.
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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.
Full textAbstract:
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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Todt, Helge. "Hydrogen-deficient central stars of planetary nebulae." Phd thesis, Universität Potsdam, 2009. http://opus.kobv.de/ubp/volltexte/2010/4104/.
Full textAbstract:
Central stars of planetary nebulae are low-mass stars on the brink of their final evolution towards white dwarfs. Because of their surface temperature of above 25,000 K their UV radiation ionizes the surrounding material, which was ejected in an earlier phase of their evolution. Such fluorescent circumstellar gas is called a "Planetary Nebula".
About one-tenth of the Galactic central stars are hydrogen-deficient. Generally, the surface of these central stars is a mixture of helium, carbon, and oxygen resulting from partial helium burning. Moreover, most of them have a strong stellar wind, similar to massive Pop-I Wolf-Rayet stars, and are in analogy classified as [WC]. The brackets distinguish the special type from the massive WC stars.
Qualitative spectral analyses of [WC] stars lead to the assumption of an evolutionary sequence from the cooler, so-called late-type [WCL] stars to the very hot, early-type [WCE] stars.
Quantitative analyses of the winds of [WC] stars became possible by means of computer programs that solve the radiative transfer in the co-moving frame, together with the statistical equilibrium equations for the population numbers. First analyses employing models without iron-line blanketing resulted in systematically different abundances for [WCL] and [WCE] stars. While the mass ratio of He:C is roughly 40:50 for [WCL] stars, it is 60:30 in average for [WCE] stars. The postulated evolution from [WCL] to [WCE] however could only lead to an increase of carbon, since heavier elements are built up by nuclear fusion.
In the present work, improved models are used to re-analyze the [WCE] stars and to confirm their He:C abundance ratio. Refined models, calculated with the Potsdam WR model atmosphere code (PoWR), account now for line-blanketing due to iron group elements, small scale wind inhomogeneities, and complex model atoms for He, C, O, H, P, N, and Ne. Referring to stellar evolutionary models for the hydrogen-deficient [WC] stars, Ne and N abundances are of particular interest. Only one out of three different evolutionary channels, the VLTP scenario, leads to a Ne and N overabundance of a few percent by mass. A VLTP, a very late thermal pulse, is a rapid increase of the energy production of the helium-burning shell, while hydrogen burning has already ceased. Subsequently, the hydrogen envelope is mixed with deeper layers and completely burnt in the presence of C, He, and O. This results in the formation of N and Ne.
A sample of eleven [WCE] stars has been analyzed. For three of them, PB 6, NGC 5189, and [S71d]3, a N overabundance of 1.5% has been found, while for three other [WCE] stars such high abundances of N can be excluded. In the case of NGC 5189, strong spectral lines of Ne can be reproduced qualitatively by our models. At present, the Ne mass fraction can only be roughly estimated from the Ne emission lines and seems to be in the order of a few percent by mass.
Furthermore, using a diagnostic He-C line pair, the He:C abundance ratio of 60:30 for [WCE] stars is confirmed.
Within the framework of the analysis, a new class of hydrogen-deficient central stars has been discovered, with PB 8 as its first member. Its atmospheric mixture resembles rather that of the massive WNL stars than of the [WC] stars. The determined mass fractions H:He:C:N:O are 40:55:1.3:2:1.3. As the wind of PB 8 contains significant amounts of O and C, in contrast to WN stars, a classification as [WN/WC] is suggested.Zentralsterne Planetarischer Nebel sind massearme Sterne kurz vor ihrer finalen Entwicklung zu Weißen Zwergen. Aufgrund ihrer Oberflächentemperatur von über 25 000 K sind sie in der Lage, durch Abstrahlung von UV-Licht das sie umgebende Material, welches in einer vorigen Phase ihrer Entwicklung abgestoßen wurde, zu ionisieren. Das solchermaßen zum Leuchten angeregte Gas bezeichnet man als Planetarischen Nebel. Etwa ein Zehntel der galaktischen Zentralsterne sind wasserstoffarm. Im Allgemeinen besteht die Oberfläche dieser Zentralsterne aus einer Mischung der Elemente Helium, Kohlenstoff und Sauerstoff, welche z.T. durch Heliumbrennen erzeugt wurden. Die meisten dieser Sterne haben darüberhinaus einen starken Sternwind, ähnlich den massereichen Pop-I-Wolf-Rayet-Sternen und werden in Analogie zu diesen als [WC] klassifiziert, wobei die eckigen Klammern der Unterscheidung von den massereichen WC-Sternen dienen. Qualitative Analysen der Spektren von [WC]-Sternen lassen eine Entwicklungssequenz dieser Sterne von kühleren sogenannten late-type [WC]-Sternen (kurz [WCL]) zu sehr heißen, early-type [WC]-Sternen (kurz [WCE]) vermuten. Mithilfe von Computerprogrammen, die den Strahlungstransport im mitbewegten Beobachtersystem zusammen mit den statistischen Gleichungen der Besetzungszahlen der Ionen im Sternwind rechnen können, wurden quantitative Untersuchungen der Winde von [WC]-Sternen möglich. Erste Analysen mit Modellen ohne Eisenlinien ergaben dabei systematisch unterschiedliche Häufigkeiten für [WCL]- und [WCE]-Sterne. Während sich für [WCL]-Sterne ein Verhältnis der Massenanteile von He:C von etwas 40:50 ergab, fand man für die [WCE]-Sterne ein mittleres Verhältnis von 60:30 für die He:C-Massenanteile. Dabei sollte die Entwicklung von [WCL] nach [WCE] innerhalb einer sehr kurzen Zeit durch Aufheizung infolge der Kontraktion der Hülle erfolgen und nicht mit einer wesentlichen Abnahme der Kohlenstoffhäufigkeit bei gleichzeitiger Zunahme der Heliumhäufigkeit an der Oberfläche einhergehen. Im Rahmen der vorgelegten Arbeit wird untersucht, ob sich mittels verbesserter Modelle für die Atmosphären von [WC]-Sternen das He:C-Häufigkeitsverhältnis der [WCE]-Sterne bestätigt. Elaboriertere Modelle, welche vom Potsdamer WR-Modelatmosphären-Code (PoWR) berechnet werden können, berücksichtigen Line-Blanketing aufgrund von Elementen der Eisengruppe, kleinskalige Windinhomogenitäten und die Elemente He, C, O, H, P, N und Ne. Unter Bezug auf Sternentwicklungsmodelle, die die Ursache der Wasserstoffunterhäufigkeit von [WC]-Sternen erklären, sind insbesondere die Neon- und Stickstoff-Häufigkeiten interessant. Von den drei möglichen Entwicklungskanälen für [WC]-Sterne führt lediglich das VLTP-Szenario zu einer Stickstoff-Überhäufigkeit von einigen Prozent bezogen auf die Masse. Bei einem VLTP, einem very late thermal pulse, handelt es sich um einen plötzlichen, starken Anstieg der Energieproduktion in der helium-brennenden Schale, während das Wasserstoffbrennen bereits zum Erliegen gekommen ist. Infolge eines VLTPs wird sämtlicher Wasserstoff kurz nach dem thermischen Puls in tiefere Schichten gemischt und in Anwesenheit von C, He und O verbrannt. Infolgedessen wird N und auch Ne erzeugt. Bei der Analyse von elf [WCE]-Sternen wurden für drei von ihnen, PB 6, NGC 5189 und [S71d]3, Stickststoffmassenanteile von 1,5 % bestimmt, während für drei andere Sterne solche hohen Stickstoffhäufigkeiten ausgeschlossen werden können. Für NGC 5189 gelang außerdem die qualitative Reproduktion der beobachteten, starken Ne-Spektrallinien mittels unserer Modelle. Zur Zeit lässt sich aus der Stärke der Ne-Emissionslinien der Ne-Massenanteil leider nur abschätzen, er scheint aber im Bereich einiger Prozent zu liegen. Mittels eines diagnostischen He-C-Linienpaares konnte das He:C-Massenverhältnis von 60:30 für [WCE]-Sterne bestätigt werden. Als Ergebnis der Analyse von PB 8 postulieren wir eine neue Klasse von wasserstoffarmen Zentralsternen, die in ihrer Elementzusammensetzung eher an massereiche WNL-Sterne als an [WC]-Sterne erinnern. Die ermittelten Massenanteile H:He:C:N:O betragen 40:55:1.3:2:1.3, der Wind von PB 8 enthält daher im Unterschied zu WN-Sternen signifikante Mengen von O und C. Es wird daher eine Klassifizierung als [WN/WC] vorgeschlagen.
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Baines, Ellyn K. "Inspection and Characterization of Exoplanet Using the CHARA Array." Digital Archive @ GSU, 2007. http://digitalarchive.gsu.edu/phy_astr_diss/20.
Full textAbstract:
Until the last decade or so, our entire knowledge of planets around Sun-like stars consisted of those in our own Solar System. This is no longer the case. Over 200 planets have been discovered through radial velocity surveys and photometric studies, both of which depend on observing the planet's effects on its host star. Much of our knowledge of the planets orbiting these stars is uncertain, based on assumptions about the stars' masses and the planets' orbital inclinations. This dissertation is comprised of two main sections. The first involves measuring the angular diameters for a sample of exoplanet host stars using Georgia State University's CHARA Array in order to learn more about the nature of these stars. These direct angular measurements are not dependent on the exoplanet systems' inclinations or the masses of the stars. Improved angular diameters lead to linear diameters when combined with HIPPARCOS parallax measurements, which in turn tell us of the stars' ages and masses. Of the 82 exoplanet systems observable with the CHARA Array, 31 host stars were observed and stellar angular diameters were measured for 26 systems. In the special case of an exoplanet system with a transiting planet, this direct measurement of the star's angular diameter leads to a direct measurement of the planet's diameter, when the planet-to-star-radii ratio is known from photometric studies. This was done for HD 189733. The star's angular diameter is 0.377 +/- 0.024 mas, which produces a stellar linear radius of 0.779 +/- 0.052 R_Sun and a planetary diameter of 1.19 +/- 0.08 R_Jupiter. The second part of this project involved the inspection of the exoplanet systems for stellar companions masquerading as planets. From radial velocity studies alone, it is impossible to distinguish between a planet in a high-inclination orbit and a low-mass stellar companion in a low-inclination orbit. Using the CHARA Array, it was possible to rule out certain secondary spectral types for each exoplanet system observed by studying the errors in the diameter fit and searching for separated fringe packets. While no definitive stellar companions were found, two expolanet systems, upsilon Andromedae and rho Coronae Borealis, exhibited behavior that were not consistent with the host star being a simple limb-darkened disk.
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Brown, David John Alexander. "The effects of tidal interactions on the properties and evolution of hot-Jupiter planetary systems." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/4181.
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Thanks to a range of discovery methods that are sensitive to different regions of parameter space, we now know of over 900 planets in over 700 planetary systems. This large population has allowed exoplanetary scientists to move away from a focus on simple discovery, and towards efforts to study the bigger pictures of planetary system formation and evolution. The interactions between planets and their host stars have proven to be varied in both mechanisms and scope. In particular, tidal interactions seem to affect both the physical and dynamical properties of planetary systems, but characterising the broader implications of this has proven challenging. In this thesis I present work that investigates different aspects of tidal interactions, in order to uncover the scope of their influence of planetary system evolution. I compare two different age calculation methods using a large sample of exoplanet and brown dwarf host stars, and find a tendency for stellar model fitting to supply older age estimates than gyrochronology, the evaluation of a star's age through its rotation (Barnes 2007). Investigating possible sources of this discrepancy suggests that angular momentum exchange through the action of tidal forces might be the cause. I then select two systems from my sample, and investigate the effect of tidal interactions on their planetary orbits and stellar spin using a forward integration scheme. By fitting the resulting evolutionary tracks to the observed eccentricity, semi-major axis and stellar rotation rate, and to the stellar age derived from isochronal fitting, I am able to place constraints on tidal dissipation in these systems. I find that the majority of evolutionary histories consistent with my results imply that the stars have been spun up through tidal interactions as the planets spiral towards their Roche limits. I also consider the influence of tidal interactions on the alignment between planetary orbits and stellar spin, presenting new measurements of the projected spin-orbit alignment angle, λ, for six hot Jupiters. I consider my results in the context of the full ensemble of measurements, and find that they support a previously identified trend in alignment angle with tidal timescale, implying that tidal realignment might be responsible for patterns observed in the λ distribution.
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Gaspar, Andras. "Observations and Models of Infrared Debris Disk Signatures and their Evolution." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202982.
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In my thesis I investigate the occurrence of mid-infrared excess around stars and their evolution. Since the launch of the first infrared satellite, IRAS, we have known that a large fraction of stars exhibit significant levels of infrared emission above their predicted photospheric level. Resolved optical and infrared images have revealed the majority of these excesses to arise from circumstellar disk structures, made up of distributions of planetesimals, rocks, and dust. These structures are descriptively called debris disks. The first part of my thesis analyzes the Spitzer Space Telescope Observations of δ Velorum. The 24 μm Spitzer images revealed a bow shock structure in front of the star. My analysis showed that this is a result of the star’s high speed interaction with the surrounding interstellar medium. We place this observation and model in context of debris disk detections and the origin of λ Boötis stars. The second part of my thesis summarizes our observational results on the open cluster Praesepe. Using 24 μm data, I investigated the fraction of stars with mid-infrared excess, likely to have debris disks. I also assembled all results from previous debris disk studies and followed the evolution of the fraction of stars with debris disks. The majority of debris disks systems are evolved, few hundred million or a Gyr old. Since the dissipation timescale for the emitting dust particles is less than the age of these systems, they have to be constantly replenished through collisional grinding of the larger bodies. The last two chapters of my thesis is a theoretical analysis of the collisional cascade in debris disks, the process that produces the constant level of dust particles detected. I introduce a numerical model that takes into account all types of destructive collisions in the systems and solves the full scattering equation. I show results of comparisons between my and other published models and extensive verification tests of my model. I also analyze the evolution of the particle size distribution as a function of the variables in my model and show that the model itself is quite robust against most variations.
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Raghavan, Deepak. "A Survey of Stellar Families: Multiplicity of Solar-type Stars." unrestricted, 2009. http://etd.gsu.edu/theses/available/etd-04212009-165714/.
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Thesis (Ph. D.)--Georgia State University, 2009.Title from file title page. Harold A. McAlister, committee chair; Russel J. White, Brian D. Mason, Douglas R. Gies, David W. Latham, A.G. Unil Perera, Todd J. Henry, committee members. Description based on contents viewed Aug. 24, 2009. Includes bibliographical references (p. 391-410).
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Ngo, Henry, Heather A. Knutson, Sasha Hinkley, Marta Bryan, Justin R. Crepp, Konstantin Batygin, Ian Crossfield, et al. "FRIENDS OF HOT JUPITERS. IV. STELLAR COMPANIONS BEYOND 50 au MIGHT FACILITATE GIANT PLANET FORMATION, BUT MOST ARE UNLIKELY TO CAUSE KOZAI–LIDOV MIGRATION." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621385.
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Stellar companions can influence the formation and evolution of planetary systems, but there are currently few observational constraints on the properties of planet-hosting binary star systems. We search for stellar companions around 77 transiting hot Jupiter systems to explore the statistical properties of this population of companions as compared to field stars of similar spectral type. After correcting for survey incompleteness, we find that 47% +/- 7% of hot Jupiter systems have stellar companions with semimajor axes between 50 and 2000 au. This is 2.9 times larger than the field star companion fraction in this separation range, with a significance of 4.4 sigma. In the 1-50 au range, only 3.9(-2.0)(+4.5)% of hot Jupiters host stellar companions, compared to the field star value of 16.4% +/- 0.7%, which is a 2.7 sigma difference. We find that the distribution of mass ratios for stellar companions to hot Jupiter systems peaks at small values and therefore differs from that of field star binaries which tend to be uniformly distributed across all mass ratios. We conclude that either wide separation stellar binaries are more favorable sites for gas giant planet formation at all separations, or that the presence of stellar companions preferentially causes the inward migration of gas giant planets that formed farther out in the disk via dynamical processes such as Kozai-Lidov oscillations. We determine that less than 20% of hot Jupiters have stellar companions capable of inducing Kozai-Lidov oscillations assuming initial semimajor axes between 1 and 5 au, implying that the enhanced companion occurrence is likely correlated with environments where gas giants can form efficiently.
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Lyra, Wladimir. "Turbulence-Assisted Planetary Growth : Hydrodynamical Simulations of Accretion Disks and Planet Formation." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9537.
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The current paradigm in planet formation theory is developed around a hierarquical growth of solid bodies, from interstellar dust grains to rocky planetary cores. A particularly difficult phase in the process is the growth from meter-size boulders to planetary embryos of the size of our Moon or Mars. Objects of this size are expected to drift extremely rapid in a protoplanetary disk, so that they would generally fall into the central star well before larger bodies can form. In this thesis, we used numerical simulations to find a physical mechanism that may retain solids in some parts of protoplanetary disks long enough to allow for the formation of planetary embryos. We found that such accumulation can happen at the borders of so-called dead zones. These dead zones would be regions where the coupling to the ambient magnetic field is weaker and the turbulence is less strong, or maybe even absent in some cases. We show by hydrodynamical simulations that material accumulating between the turbulent active and dead regions would be trapped into vortices to effectively form planetary embryos of Moon to Mars mass. We also show that in disks that already formed a giant planet, solid matter accumulates on the edges of the gap the planet carves, as well as at the stable Lagrangian points. The concentration is strong enough for the solids to clump together and form smaller, rocky planets like Earth. Outside our solar system, some gas giant planets have been detected in the habitable zone of their stars. Their wakes may harbour rocky, Earth-size worlds.
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Smith, Alexis Michael Sheridan. "Searching for transiting extra-solar planets at optical and radio wavelengths." Thesis, St Andrews, 2009. http://hdl.handle.net/10023/871.
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Luttermoser, Donald G. "The Infrared Spectra of Mira Stars." Digital Commons @ East Tennessee State University, 2014. https://dc.etsu.edu/etsu-works/711.
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Over the past two decades, much has been learned about the atmospheric structure of the pulsating Mira-type variable stars from computer modeling and the analysis of ultraviolet and visible wavelength spectra. This talk reports on the first set of infrared spectra taken of these stars under high dispersion with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. A sample of 25 galactic Miras was observed in the 10-37 micron spectral regime anywhere from two to several times during their pulsation cycle. Many of the stars observed show marked changes in overall flux levels as a function of phase. We are able to identify many strong emission lines from neutral and singly ionized metals and emission features due to silicate and carbon dusts and molecular constituents. This work was financially supported through a NASA Spitzer grant for Program GO 50717.
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Yu, Louise. "Recherche de Jupiters chauds autour d'étoiles jeunes." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30240.
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Les 25 dernières années ont vu la détection d'environ 400 Jupiters chauds (hJs), exoplanètes géantes semblables à Jupiter mais sur des orbites cent fois plus resserrées. Ces planètes étonnantes se seraient formées loin de leur étoile avant de migrer vers elle, cependant les processus physiques à l'origine de ce transfert orbital sont encore peu contraints par les observations. Cette question, essentielle à notre compréhension de la formation des systèmes planétaires, a de profondes répercussions sur l'architecture de ces systèmes, et en particulier sur la probabilité de former des planètes telles que la Terre dans la zone habitable des étoiles. Afin de mieux contraindre l'évolution orbitale précoce des systèmes planétaires, nous analysons des données recueillies dans le cadre du programme MaTYSSE pour rechercher des hJs autour d'étoiles T Tauri à raies faibles (wTTSs), c'est-à-dire de très jeunes étoiles de type solaire qui n'accrètent plus. L'objectif principal de MaTYSSE est de caractériser l'importante activité magnétique des wTTSs. Cette activité rend la détection de hJs difficile, en effet, nous recherchons des hJs par la technique de vélocimétrie, mais la forte présence de taches sombres et de plages brillantes magnétiques à la surface des wTTSs ajoute une perturbation dans les vitesses radiales (RVs), d'amplitude bien supérieure à celle attendue d'une signature de hJ. Dans cette thèse, nous modélisons l'activité magnétique des wTTSs TAP 26 et V410 Tau et filtrons la perturbation des RVs due à l'activité. Nous présentons également les résultats MaTYSSE sur l'étoile V830 Tau pour comparaison. En utilisant l'imagerie Zeeman-Doppler sur des jeux de données spectropolarimétriques pour reconstruire les distributions surfaciques de brillance et les topologies magnétiques, nous obtenons des couvertures en taches et plages de 10 - 18 % et des champs de 300 - 600 G. Les trois étoiles présentent une variabilité intrinsèque non expliquée par la rotation différentielle. La perturbation RV due à l'activité est modélisée à l'aide de deux méthodes indépendantes : nous la dérivons à partir de nos cartes ZDI, ou nous appliquons la régression par processus gaussiens aux RVs brutes. Les deux méthodes s'accordent sur la détection d'un hJ autour de V830 Tau et d'un autre autour de TAP 26. V830 Tau b, âgé de ~2 Myr, a un M sin i de 0.57 ± 0.10 MJup et orbite à 0.057 ± 0.001 au de son étoile (période orbitale 4.93 d). En raison de la fenêtre d'observation, la période orbitale de TAP 26 b ne peut être déterminée de façon unique ; le cas le plus probable est un hJ avec M sin i = 1.66 ± 0.31 MJup sur une orbite de demi-grand axe 0.0968 ± 0.0032 au (période orbitale 10.79 ± 0.14 d).[...]The past 25 years have seen the detection of about 400 hot Jupiters (hJs), giant exoplanets similar to Jupiter but orbiting their star a hundred times closer than Jupiter does the Sun. These puzzling planets are believed to have formed far from their star before migrating inwards, however the physical processes that drive this orbital transfer are still poorly constrained by observations. This question, essential to our understanding of planetary system formation, has profound implications for the architecture of these systems, and in particular for the probability of forming planets like the Earth in the habitable zone of stars. In order to better constrain the early orbital evolution of planetary systems, we analyze data collected within the frame of the MaTYSSE programme to search for hJs around weak-line T Tauri stars (wTTSs), i.e. very young Sun-like stars that stopped accreting. The main goal of MaTYSSE is to characterize the high magnetic activity of wTTSs. This activity makes hJ detection difficult, indeed, we look for hJs with the velocimetry technique, but the strong presence of magnetic dark spots and bright plages on the surface of wTTSs adds a jitter in the radial velocities (RVs), of much greater amplitude than that expected of a hJ signature. In this thesis, we model the magnetic activity of wTTSs TAP 26 and V410 Tau and filter the activity jitter out of their RVs. We also present the MaTYSSE results for star V830 Tau, for comparison. Using Zeeman-Doppler Imaging on spectropolarimetric data sets to reconstruct surface brightness distributions and magnetic topologies, we derive spot-and-plage coverages of 10 - 18 % and field strengths of 300 - 600 G. All three stars exhibit intrinsic variability not explained by differential rotation. The activity jitter is modelled with two independent methods: deriving it from our ZDI maps, or applying Gaussian Process Regression to the raw RVs. Both methods concur on the detection of a hJ around V830 Tau and another around TAP 26. The ~2 Myr V830 Tau b has a M sin i of 0.57 ± 0.10 MJup and orbits at 0.057 ± 0.001 au from its star (orbital period 4.93 d). Due to the observing window, the orbital period of TAP 26 b cannot be uniquely determined; the case with highest likelihood is a hJ with M sin i = 1.66 ± 0.31 MJup on an orbit of semi-major axis 0.0968 ± 0.0032 au (orbital period 10.79 ± 0.14 d).[...]
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"The Diversity of Chemical Composition and the Effects on Stellar Evolution and Planetary Habitability." Doctoral diss., 2017. http://hdl.handle.net/2286/R.I.45482.
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abstract: I present a catalog of 1,794 stellar evolution models for solar-type and low-mass stars, which is intended to help characterize real host-stars of interest during the ongoing search for potentially habitable exoplanets. The main grid is composed of 904 tracks, for 0.5-1.2 M_sol at scaled metallicity values of 0.1-1.5 Z_sol and specific elemental abundance ratio values of 0.44-2.28 O/Fe_sol, 0.58-1.72 C/Fe_sol, 0.54-1.84 Mg/Fe_sol, and 0.5-2.0 Ne/Fe_sol. The catalog includes a small grid of late stage evolutionary tracks (25 models), as well as a grid of M-dwarf stars for 0.1-0.45 M_sol (856 models). The time-dependent habitable zone evolution is calculated for each track, and is strongly dependent on stellar mass, effective temperature, and luminosity parameterizations. I have also developed a subroutine for the stellar evolution code TYCHO that implements a minimalist coupled model for estimating changes in the stellar X-ray luminosity, mass loss, rotational velocity, and magnetic activity over time; to test the utility of the updated code, I created a small grid (9 models) for solar-mass stars, with variations in rotational velocity and scaled metallicity. Including this kind of information in the catalog will ultimately allow for a more robust consideration of the long-term conditions that orbiting planets may experience.
In order to gauge the true habitability potential of a given planetary system, it is extremely important to characterize the host-star's mass, specific chemical composition, and thus the timescale over which the star will evolve. It is also necessary to assess the likelihood that a planet found in the "instantaneous" habitable zone has actually had sufficient time to become "detectably" habitable. This catalog provides accurate stellar evolution predictions for a large collection of theoretical host-stars; the models are of particular utility in that they represent the real variation in stellar parameters that have been observed in nearby stars.Dissertation/Thesis
Doctoral Dissertation Astrophysics 2017
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Johnas, Christine M. S. [Verfasser]. "Non-analytical line profiles in stellar atmospheres : for planetary host star systems / vorgelegt von Christine M. S. Johnas." 2008. http://d-nb.info/987361937/34.
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Lee, Duane Morris. "Understanding the Nature of Stellar Chemical Abundance Distributions in Nearby Stellar Systems." Thesis, 2014. https://doi.org/10.7916/D84747X6.
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Since stars retain signatures of their galactic origins in their chemical compositions, we can exploit the chemical abundance distributions that we observe in stellar systems to put constraints on the nature of their progenitors. In this thesis, I present results from three projects aimed at understanding how high resolution spectroscopic observations of nearby stellar systems might be interpreted. The first project presents one possible explanation for the origin of peculiar abundance distributions observed in ultra-faint dwarf satellites of the Milky Way. The second project explores to what extent the distribution of chemical elements in the stellar halo can be used to trace Galactic accretion history from the birth of the Galaxy to the present day. Finally, a third project focuses on developing an input optimization algorithm for the second project to produce better estimates of halo accretion histories. In conclusion, I propose some other new ways to use statistical models and techniques along with chemical abundance distribution data to uncover galactic histories.
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Robinson, Connor Edward. "Accretion variability in young, low-mass stellar systems." Thesis, 2020. https://hdl.handle.net/2144/42027.
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Through the study of accretion onto the young, low-mass stars known as T Tauri Stars (TTS), we can better understand the formation of our solar system. Gas is funneled along stellar magnetic field lines into magnetospheric accretion columns where it reaches free-fall velocities and shocks at the stellar surface, generating emission that carries information about the inner regions of the protoplanetary disk. Accretion is a variable process, with characteristic timescales ranging from minutes to years. In this dissertation, I use simulations, models, and observations to provide insight into the driving forces of mass accretion rate variability on timescales of minutes to weeks and the structure of the inner disk. Using hydrodynamic simulations, I find that steady-state, transonic accretion occurs naturally in the absence of any other source of variability. If the density in the inner disk varies smoothly in time with roughly day-long time-scales (e.g., due to turbulence), traveling shocks develop within the accretion column, which lead to rapid increases in the accretion luminosity followed by slower declines. I present the largest Hubble Space Telescope (HST) spectral variability study of TTS to date. I infer mass accretion rates and accretion column surface coverage using newly updated accretion shock models. I find typical changes in the mass accretion rate of order 10% and moderate changes in the surface coverage for most objects in the sample on week timescales. Individual peculiar epochs are further discussed. I find that the inner disk is inhomogeneous and that dust may survive near the magnetic truncation radius. Next, I link 2-minute cadence light curves from the Transiting Exoplanet Survey Satellite (TESS) to accretion using ground-based U-band photometry. Additional HST observations for one target enable more detailed connections between TESS light curves and accretion. I also use the TESS light curves to identify rotation periods and patterns of quasi-periodicity. Finally, I connect hydrodynamic simulations, accretion shock models, and stellar rotation to predict signatures of a turbulent inner disk. I generate light curves from these models to make comparisons to previous month-long photometric monitoring surveys of TTS using metrics of light curve symmetry and periodicity.
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Kratter, Kaitlin Michelle. "Accretion Disks and the Formation of Stellar Systems." Thesis, 2010. http://hdl.handle.net/1807/26283.
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In this thesis, we examine the role of accretion disks in the formation of stellar systems, focusing on young massive disks which regulate the flow of material from the parent molecular core down to the star. We study the evolution of disks with high infall rates that develop strong gravitational instabilities. We begin in chapter 1 with a review of the observations and theory which underpin models for the earliest phases of star formation and provide a brief review of basic accretion disk physics, and the numerical methods which we employ. In chapter 2 we outline the current models of binary and multiple star formation, and review their successes and shortcomings from a theoretical and observational perspective. In chapter 3 we begin with a relatively simple analytic model for disks around young, very massive stars, showing that instability in these disks may be responsible for the higher multiplicity fraction of massive stars, and perhaps the upper mass to which they grow. We extend these models in chapter 4 to explore the properties of disks and the formation of binary companions across a broad range of stellar masses. In particular, we model the role of global and local mechanisms for angular momentum transport in regulating the relative masses of disks and stars. We follow the evolution of these disks throughout the main accretion phase of the system, and predict the trajectory of disks through parameter space. We follow up on the predictions made in our analytic models with a series of high resolution, global numerical experiments in chapter 5. Here we propose and test a new parameterization for describing rapidly accreting, gravitationally unstable disks. We find that disk properties and system multiplicity can be mapped out well in this parameter space. Finally, in chapter 6, we address whether our studies of unstable disks are relevant to recently detected massive planets on wide orbits around their central stars.
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Sandford, Emily Ruth. "The Shapes of Planet Transits and Planetary Systems." Thesis, 2020. https://doi.org/10.7916/d8-jqt7-9a41.
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In this Thesis, I explore transiting exoplanets: what we can learn from modeling their light curves, and what we can learn from their arrangement in planetary systems. I begin in Chapter 1 by briefly reviewing the history of transit modeling, from the earliest theoretical models of eclipsing binary stars to the models in current widespread use to model exoplanet transits. In Chapter 2, I model the transits of a sample of Kepler exoplanets with strong prior eccentricity constraints in order to derive correspondingly strong constraints on the density of their host stars, and find that the density constraints I derive are as precise as density constraints from asteroseismology if the transits are observed at high signal-to-noise. In Chapter 3, I apply the same methodology in reverse: using prior knowledge of the stellar density based on Gaia parallax measurements, I model the transits of twelve singly-transiting planets observed by K2 and derive constraints on their periods. In Chapter 4, I consider the general problem of deducing the shape of a transiting object from its light curve alone, which I term ``shadow imaging;'' I explore the mathematical degeneracies of the problem and construct shadow images to explain Dips 5 and 8 of Boyajian's Star.
I next turn to multi-planet systems: in Chapter 5, I investigate the underlying multiplicity distribution of planetary systems orbiting FGK dwarfs observed by Kepler. I find that we can explain the multiplicities of these systems with a single Zipfian multiplicity distribution, without invoking a dichotomous population. In Chapter 6, I consider the arrangement of planets in those systems, and use neural networks inspired by models used for part-of-speech tagging in computational linguistics to model the relationship between exoplanets and their surrounding "context," i.e. their host star and sibling planets. I find that our trained regression model is able to predict the period and radius of an exoplanet to a factor of two better than a naive model which only takes into account basic dynamical stability. I also find that our trained classification model identifies consistent classes of planets in the period-radius plane, and that it is rare for multi-planet systems to contain a neighboring pair of planets from non-contiguous classes.
In Chapter 7, I summarize these results and briefly discuss avenues for future work, including the application of our methods to planets and planetary systems discovered by TESS.
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"Stellar Abundances in the Solar Neighborhood." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.14765.
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abstract: The only elements that were made in significant quantity during the Big Bang were hydrogen and helium, and to a lesser extent lithium. Depending on the initial mass of a star, it may eject some or all of the unique, newly formed elements into the interstellar medium. The enriched gas later collapses into new stars, which are able to form heavier elements due to the presence of the new elements. When we observe the abundances in a stellar regions, we are able to glean the astrophysical phenomena that occurred prior to its formation. I compile spectroscopic abundance data from 49 literature sources for 46 elements across 2836 stars in the solar neighborhood, within 150 pc of the Sun, to produce the Hypatia Catalog. I analyze the variability of the spread in abundance measurements reported for the same star by different surveys, the corresponding stellar atmosphere parameters adopted by various abundance determination methods, and the effect of normalizing all abundances to the same solar scale. The resulting abundance ratios [X/Fe] as a function of [Fe/H] are consistent with stellar nucleosynthetic processes and known Galactic thin-disk trends. I analyze the element abundances for 204 known exoplanet host-stars. In general, I find that exoplanet host-stars are not enriched more than the surrounding population of stars, with the exception of iron. I examine the stellar abundances with respect to both stellar and planetary physical properties, such as orbital period, eccentricity, planetary mass, stellar mass, and stellar color. My data confirms that exoplanet hosts are enriched in [Fe/H] but not in the refractory elements, per the self-enrichment theory for stellar composition. Lastly, I apply the Hypatia Catalog to the Catalog of Potentially Habitable Stellar Systems in order to investigate the abundances in the 1224 overlapping stars. By looking at stars similar to the Sun with respect to six bio-essential elements, I created maps that have located two ``habitability windows'' on the sky: (20.6hr, -4.8deg) and (22.6hr, -48.5deg). These windows may be of use in future targeted or beamed searches.Dissertation/Thesis
Ph.D. Astrophysics 2012
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"Variability of Elemental Abundances in the Local Neighborhood and its Effect on Planetary Systems." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.25050.
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abstract: As the detection of planets become commonplace around our neighboring stars, scientists can now begin exploring their possible properties and habitability. Using statistical analysis I determine a true range of elemental compositions amongst local stars and how this variation could affect possible planetary systems. Through calculating and analyzing the variation in elemental abundances of nearby stars, the actual range in stellar abundances can be determined using statistical methods. This research emphasizes the diversity of stellar elemental abundances and how that could affect the environment from which planets form. An intrinsic variation has been found to exist for almost all of the elements studied by most abundance-finding groups. Specifically, this research determines abundances for a set of 458 F, G, and K stars from spectroscopic planet hunting surveys for 27 elements, including: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, La, Ce, Nd, Eu, and Hf. Abundances of the elements in many known exosolar planet host stars are calculated for the purpose investigating new ways to visualize how stellar abundances could affect planetary systems, planetary formation, and mineralogy. I explore the Mg/Si and C/O ratios as well as place these abundances on ternary diagrams with Fe. Lastly, I emphasize the unusual stellar abundance of τ Ceti. τ Ceti is measured to have 5 planets of Super-Earth masses orbiting in near habitable zone distances. Spectroscopic analysis finds that the Mg/Si ratio is extremely high (~2) for this star, which could lead to alterations in planetary properties. τ Ceti's low metallicity and oxygen abundance account for a change in the location of the traditional habitable zone, which helps clarify a new definition of habitable planets.Dissertation/Thesis
Ph.D. Astrophysics 2014
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Broekhoven-Fiene, Hannah. "Resolving the multi-temperature debris disk around γ Doradus with Herschel." Thesis, 2011. http://hdl.handle.net/1828/3758.
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We present Herschel observations of the debris disk around γ Doradus (HD 27290, HIP 19893) from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free Reconnaissance in the Infrared/Submillimetre). The disk is well-resolved with PACS at 70, 100 and 160 micron and detected with SPIRE at 250 and 350 micron. The 250 micron image is only resolved along the disk's long axis. The SPIRE 500 micron 3 σ detection includes a nearby background source. γ Dor's spectral energy distribution (SED) is sampled in the submillimetre for the first time and modelled with multiple modified-blackbody functions to account for its broad shape. Two approaches are used, both of which reproduce the SED in the same way: a model of two narrow dust rings and a model of an extended, wide dust belt. The former implies the dust rings have temperatures of ~90 and ~40 K, corresponding to blackbody radii of 25 and 135 AU, respectively. The latter model suggests the dust lies in a wide belt extending from 15 to 230 AU. The resolved images, however, show dust extending beyond ~350 AU. This is consistent with other debris disks whose actual radii are observed to be a factor of 2 - 3 times larger than the blackbody radii. Although it is impossible to determine a preferred model from the SED alone, the resolved images suggest that the dust is located in a smooth continuous belt rather than discrete narrow rings. Both models estimate that the dust mass is 6.7 x 10^{-3} Earth masses and that fractional luminosity is 2.5 x 10^{-5}. This amount of dust is within the levels expected from steady state evolution given the age of γ Dor and therefore a transient event is not needed to explain the dust mass. No asymmetries that would hint at a planetary body are evident in the disk at Herschel's resolution. However, the constraints placed on the dust's location suggest that the most likely region to find planets is within 20 AU of the star.Graduate
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Saffe, Jameson Carlos Emilio. "Propiedades físicas de estrellas con exoplanetas y anillos circunestelares /." Doctoral thesis, 2008. http://hdl.handle.net/11086/122.
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Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2008.Estudiamos diferentes aspectos de estrellas con exoplanetas (EH) y de estrellas de tipo Vega. Detectamos excesos IR en 20% de las estrellas EH, el cual se atribuye a la presencia de polvo circunestelar.
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Villarreal, D'Angelo Carolina Susana. "Estudio numérico de la interacción entre vientos estelares y planetarios." Doctoral thesis, 2016. http://hdl.handle.net/11086/4129.
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tesis (doctor en astronomía)--universidad nacional de córdoba, facultad de matemática, astronomía, física y computación, 2016.en esta tesis se estudió, mediante simulaciones numéricas (hidrodinámicas y magnetohidrodinámicas), el escape atmosférico del exoplaneta hd 209458b y su interacción con el viento y la radiación estelar. los resultados numéricos se comparan con el rasgo más distintivo de este sistema, las observaciones de tránsito en la línea de emisión ly-α. las mismas han sido exhaustivamente estudiadas y analizadas, confirmando la presencia de material neutro escapando del planeta. para poder incluir la presencia de los campos magnéticos en los modelos, fue necesario adaptar el código numérico con el fin de resolver las ecuaciones de la mhd. todos los modelos numéricos tienen en cuenta la gravedad del planeta y la estrella, la presión de radiación y los procesos radiativos involucrados. como resultado principal, se logró restringir el valor de la tasa de pérdida de masa planetaria y los parámetros del viento estelar.
in this thesis i studied, by means of numerical simulations (hydrodynamics and magnetohydrodynamics), the atmospheric escape of hd 209458b and his interaction with the stellar wind and radiation. the numerical results are compared with the most distinguished feature of this planetary system, the transits observations of the stellar emision lyα line. this line have been extensively studied and analyzed, confirming the presence of neutral material escaping from the planet. in order to include in the models the presence of magnetic fields, the numerical code was adapted to resolve the mhd equations. all the numerical models take into account the gravity of the planet and the star, the radiation pressure and the radiative process involved. as a main result, it was possible to constrain the planetary mass loss rate and the stellar wind parameters.
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Lovos, Flavia Virginia. "Estudio de variabilidad fotométrica en estrellas de tipo T Tauri." Doctoral thesis, 2019. http://hdl.handle.net/11086/14315.
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Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2019.Las estrellas jóvenes de tipo T Tauri tienen la edad adecuada para el inicio del proceso de formación planetaria de acuerdo a los modelos más aceptados en la actualidad. Sin embargo éstas presentan algunos desafíos para la técnica clásica de detección de planetas extrasolares mediante tránsitos planetarios. Principalmente las T Tauri manifiestan diversas formas de variabilidad que, mayormente, se evidencian en sus curvas de luz. En este trabajo se presenta un análisis y caracterización de la variabilidad fotométrica de 52 estrellas T Tauri australes, a partir de datos propios obtenidos desde el CASLEO y de la EABA, como primer paso para comprender cómo esta variabilidad puede influir en la detectabilidad de potenciales embriones planetarios transitantes. Entre los tipos de variabilidad observados, el más frecuente se debe a la presencia de manchas sobre la superficie estelar, así como otros relacionados con procesos de acreción y/o obscurecimiento por polvo en discos circunestelares.
Young pre-main sequence stars of T Tauri type have appropriate ages for the beginning of the planetary formation process according to the currently most accepted models. However, T Tauri stars offer some challenges for the classical techniques of extrasolar planets detection by means of planetary transits. Principally, T Tauri stars have different types of variability that are mostly evident in their light curves. In this work is presented an analysis and characterization of the photometric variability of 52 southern T Tauri stars, from data obtained from the CASLEO and the EABA observatories, as a first step to learn how such variability may affect the detectability of transiting planetary embryos. Among the types of variabilities, the most frequent are due to the presence of spots on the stellar surfaces, as well as others related to processes of accretion and/or darkening by dust in the circumstellar disks.
Lovos, Flavia Virginia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.
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Saker, Leila Yamila. "Material circunestelar en estrellas de tipo enanas blancas." Doctoral thesis, 2020. http://hdl.handle.net/11086/23533.
Full textAbstract:
Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2020.Se han descubierto discos de gas en un grupo de enanas blancas con discos de polvo, a través de la detección en sus espectros de lineas de emisión inusuales del triplete de Ca II en 8600 Å. En este contexto, se han obtenido espectros ópticos GMOS/GEMINI para 13 enanas blancas con excesos IR, seleccionados de nuestra muestra de 29 estrellas con discos “debris”, con el objetivo de encontrar la contraparte gaseosa a los discos de polvo. Se presenta además un estudio comparativo de las principales propiedades físicas y de parámetros relacionados al disco de polvo de las enanas blancas con y sin discos de gas detectados. Adicionalmente, se aplicó la técnica de “Eclipse Timing Variation” en una muestra de 8 sistemas binarios eclipsantes formados por enana blanca+estrella de secuencia principal con el objetivo de detectar planetas circumbinarios. Para ello, se obtuvieron observaciones propias con los telescopios argentinos localizados en la Estación Astrofísica de Bosque Alegre y el telescopio Jorge Sahade en el Complejo Astronómico El Leoncito. Las curvas de luz obtenidas, fueron complementadas con las disponibles en las bases de datos del “Catalina Sky Survey” y Kepler+K2. Los tiempos de mínimo fueron obtenidos con el código Wilson & Devinney.
Gas disks have been discovered in a group of white dwarfs with dust disks, through the detection in their spectra of unusual emission lines of the triplet of Ca II at 8600 Å. In this context, GMOS/GEMINI optical spectra have been obtained for 13 white dwarfs with IR excesses, selected from our sample of 29 stars with debris disks, with the aim to find the gaseous counterpart to the dusty disks. We also present a comparative study of the main physical properties and parameters related to the dusty disk of white dwarfs with and without gas disks detected. Additionally, the Eclipse Timing Variation technique was applied in a sample of 8 eclipsing binary systems formed by white dwarf + main sequence star, with the aim to detect circumbinary planets. For this, own observations were obtained with the Argentine telescopes located in the Estación Astrofísica de Bosque Alegre and the Jorge Sahade telescope in the Complejo Astronómico El Leoncito. The light curves obtained were complemented with those available in the databases "Catalina Sky Survey" and Kepler+K2. Minimum times were obtained with the Wilson & Devinney code.
Fil: Saker, Leila Yamila. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.
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Blouin, Simon. "Modélisation des effets de haute densité à la photosphère des naines blanches froides." Thèse, 2019. http://hdl.handle.net/1866/22671.
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