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Model atmospheres of sub-stellar mass objectsHubeny, Ivan 07 1900 (has links)
We present an outline of basic assumptions and governing structural equations describing atmospheres of sub-stellar mass objects, in particular the extrasolar giant planets and brown dwarfs. Although most of the presentation of the physical and numerical background is generic, details of the implementation pertain mostly to the code COOLTLUSTY. We also present a review of numerical approaches and computer codes devised to solve the structural equations, and make a critical evaluation of their efficiency and accuracy.
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Seleção de candidatos a sistemas planetários jovens / Selection of candidates for young planetary systemsMatheus, Thiago 25 May 2010 (has links)
Os modelos atuais sobre formação planetária indicam que os planetas gasosos gigantes formam-se em escalas de tempo de ~ 10 Manos, inferiores à dos pequenos, rochosos, de ~ 30 Manos (Zuckerman & Song 2004). Um teste simples desses modelos de formação seria procurar planetas em torno de estrelas jovens de várias idades: nos sistemas mais jovens não dever-se-ia detectar objetos telúricos, que só apareceriam em torno de estrelas relativamente mais velhas. Os satélites CoRoT e Kepler, que se encontram em pleno regime de observações, vêm descobrindo exoplanetas pelo método dos trânsitos, sendo capaz de detectar corpos de dimensões terrestres. O objetivo deste trabalho, é selecionar sistemas planetários jovens de várias idades para serem observados pelo dois satélites, a fim de testar as escalas de tempo de formação de planetas rochosos e gasosos. Para atingir esse objetivo foi necessário entender como a idade pode ser estimada para um grupo de estrelas (aglomerado aberto ou associação), utilizando-se, por exemplo, dados sobre abundâncias químicas do lítio dos objetos. Isso é possível devido à facilidade do lítio em ser destruído na fase pré-sequencia principal, a temperaturas superiores 2,5 10^6 K. Um levantamento amostral da abundância do lítio em função da temperatura, para estrelas pertecentes a um grupo, gera um padrão de depleção do lítio, que permite gerar um modelo (da Silva et al. 2009) qualitativo para se obter idades de associações estelares. Para que o propósito deste trabalho fosse alcançado, foram utilizados os bancos de dados de objetos jovens existentes em associações com idades bem determinadas de (Torres et al. 2008), e o catálogo DAML de (Dias et al. 2002) de aglomerados abertos. A seleção dos dados para cada satélite produziu resultados bem diferentes. Para o CoRoT, a análise do banco de dados de associações retornou resultados com uma associação no centro galáctico e outra de ~ 70 Manos no anti-centro; por outro lado, no campo do Kepler, não se encontrou objetos jovens que possibilitassem atender os objetivos deste trabalho. Na análise do catálogo DAML de aglomerados abertos, surgiram muitos candidatos-alvo para observações. Para o CoRoT, foi possível concluir que os aglomerados NGC 2244 de 7,87 Manos, NGC 2264 de 8,99 Manos, Collinder 107 de 10 Manos, Collinder 96 de 10,74 Manos, e NGC 2302 de 12,02 Manos contêm alvos onde deve-se encontrar somente planetas gigantes gasosos em estágio inicial e/ou final de formação, de acordo com o capítulo 1. Os aglomerados relativamente mais velhos, onde devem-se encontrar planetas rochosos e gasosos são: NGC 6755 de 52,36 Manos, Basel 1 de 78,16 Manos, NGC 6694 de 85,31 Manos, NGC 2186 de 54,70 Manos, NGC 2422 de 72,61 Manos e Bochum 3 de 77,62 Manos. Portanto a etapa de seleção de alvos a serem observados pelo CoRoT foi feita, e com isso, os eventuais resultados observacionais servirão de teste para as escalas de tempo de formação planetária propostos nos modelos correntes. Para o Kepler, não foi encontrado nenhum membro de aglomerado jovem observável em seu campo de visibilidade e seu intervalo de magnitudes. / Current models of planetary formation suggest that the giant gaseous planets are formed in time scales of ~ 10 Myr, less than the rocky ones, in time scales of ~ 30 Myr (Zuckerman & Song 2004). A simple test of these models of formation it would look for planets around young stars of various ages: in younger systems it should not detect terrestrial objects, which only appear around stars relatively older. CoRoT and Kepler satellites, which are at full system of observations, have been discovering exoplanets by the method of transits, being able to detect Earth-size bodies. The goal of this work is to select young planetary systems of various ages to be observed by the two satellites, in order to test the time scales of formation of rocky and gaseous planets. To achieve this goal it was necessary to understand how age can be estimated for a group of stars (open cluster or association), using, for example, data on chemical abundances of lithium objects. This is possible because of the ease of lithium to be destroyed in the pre-main sequence, at temperatures above 2,5 10^6 K. A sample survey of the abundance of lithium as a function of temperature for stars belonging to a group, generates a lithium depletion pattern, which creates a qualitatively model (da Silva et al. 2009) to obtain ages of star associations. For the purpose of this study was reached, the databases of objects in youth associations with well-determined ages from (Torres et al. 2008) was used, as well, the catalog DAML from (Dias et al. 2002) of open clusters. The selection of data for each satellite has produced quite different results. For CoRoT, the analysis of the database of associations returned results with a association in the galactic center and another with ~ 70 Myr in the anti-Galactic center, on the other hand, in the field of Kepler did not find young objects that would enable meet the goals of this work.. In the analysis of DAML catalog of open clusters have emerged many candidates targeted for observations. For the CoRoT was concluded that the clusters NGC 2244 of 7,87 Myr, NGC 2264 of 8,99 Myr, Collinder 107 of 10 Myr, Collinder 96 of 10,74 Myr, and NGC 2302 of 12,02 Myr contain targets where should be found only gas giant planets in the early stage and/or end of formation, in accordance with Chapter 1. The relatively older clusters, where they must be found rocky and gaseous planets are: NGC 6755 of 52,36 Myr, Basel 1 of 78,16 Myr, NGC 6694 of 85,31 Myr, NGC 2186 of 54,70 Myr, NGC 2422 of 72,61 Myr e Bochum 3 de 77,62 Myr. Therefore the step of selecting targets to be observed by the CoRoT was made, and thus, any observational results serve as a test for the timescales of planet formation proposed in the current models. For Kepler, it did not find any member of young cluster observed in its field of vision and its range of magnitudes.
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Turbulence and transport in stars and planetsJermyn, Adam Sean January 2018 (has links)
In this dissertation I have argued that the study of stars and gaseous planets has relied too heavily on simplifying assumptions. In particular, I have demonstrated that the assumptions of spherical symmetry, thermal equilibrium, dynamical equilibrium and turbulent anisotropy all hide interesting phenomena which make a true difference to the structure and evolution of these bodies. To begin I developed new theoretical tools for probing these phenomena, starting with a new model of turbulent motion which accounts for many different sources of anisotropy. Building on this I studied rotating convection zones and determined scaling relations for the magnitude of differential rotation. In slowly-rotating systems the differential rotation is characterised by a power law with exponent of order unity, while in rapidly-rotating systems this exponent is strongly suppressed by the rotation. This provides a full characterisation of the magnitude of differential rotation in gaseous convection zones, and is in reasonable agreement with a wide array of simulations and observations. I then focused on the convection zones of rotating massive stars and found them to exhibit significantly anisotropic heat fluxes. This results in significant deviations from spherical symmetry and ultimately in qualitatively enhanced circulation currents in their envelopes. Accordingly, these stars ought to live much longer and have a different surface temperature. This potentially resolves several outstanding questions such as the anomalously slow evolution of stars on the giant branch, the dispersion in the observed properties of giant stars and the difficulty stellar modelling has to form massive binary black holes. In the same vein I examined the convection zones of bloated hot Jupiters and discovered a novel feedback mechanism between non-equilibrium tidal dissipation and the thermal structure of their upper envelopes. This mechanism stabilises shallow radiative zones against the convective instability, which would otherwise take over early on in the planet's formation as it proceeds to thermal equilibrium. Hence tidal dissipation is dramatically enhanced, which serves to inject significant quantities of heat into the upper layers of the planet and causes it to inflate. This mechanism can explain most of the observed population of inflated planets. Finally, I studied material mixing in the outer layers of accreting stars and developed a method for relating the observed surface chemistry to the bulk and accreting chemistries. This enables the direct inference of properties of circumstellar material and accretion rates for a wide variety of systems.
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A Bayesian Approach to the Understanding of Exoplanet Populations and the Origin of LifeChen, Jingjing January 2018 (has links)
The study of extrasolar planets, or exoplanets for short, has developed rapidly over the last decade. While we have spent much effort building both ground-based and space telescopes to search for exoplanets, it is even more important that we use the observational data wisely to understand them. Exoplanets are of great interest to both astronomers and the general public because they have shown varieties of characteristics that we couldn't have anticipated from planets within our Solar System. To properly analyze the exoplanet populations, we need the tools of statistics. Therefore, in Chapter 1, I describe the science background as well as the statistical methods which will be applied in this thesis. In Chapter 2, I discuss how to train a hierarchical Bayesian model in detail to fit the relationship between masses and radii of exoplanets and categorize exoplanets based on that. A natural application that comes with the model is to use it for future observations of mass/radius and predict the other measurement. Thus I will show two application cases in Chapter 3. Composition of an exoplanet is also very much constrained by its mass and radius. I will show an easy way to constrain the composition of exoplanets in Chapter 4 and discuss how more complicated methods can be applied in future works.
Of even greater interest is whether there is life elsewhere in the Universe. Although the future discovery of extraterrestrial life might be totally a fluke, a clear sketched plan always gives us some directions. Research in this area is still very preliminary. Fortunately, besides directly searching for extraterrestrial life, we can also apply statistical reasoning to first estimate the rate of abiogenesis, which will give us some clue on the question of whether there is extraterrestrial life in a probabilistic way. In Chapter 5, I will discuss how different methods can constrain the abiogenesis rate in an informatics perspective.
Finally I will give a brief summary in Chapter 6.
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Infrared variability studies of low-mass stars in the field and in the Carina Nebula star forming regionKovács, Gábor January 2015 (has links)
No description available.
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The role of binary stars in searches for extrasolar planets by microlensing and astrometryDominis, Dijana January 2006 (has links)
When Galactic microlensing events of stars are observed, one usually
measures a symmetric light curve corresponding to a single lens, or
an asymmetric light curve, often with caustic crossings, in the case
of a binary lens system. In principle, the fraction of binary stars
at a certain separation range can be estimated based on the number
of measured microlensing events. However, a binary system may produce
a light curve which can be fitted well as a single lens light curve,
in particullary if the data sampling is poor and the errorbars are
large. We investigate what fraction of microlensing events produced
by binary stars for different separations may be well fitted by and
hence misinterpreted as single lens events for various observational
conditions. We find that this fraction strongly depends on the separation
of the binary components, reaching its minimum at between 0.6
and 1.0 Einstein radius, where it is still of the order of 5%
The Einstein radius is corresponding to few A.U. for typical Galactic
microlensing scenarios. The rate for misinterpretation is higher
for short microlensing events lasting up to few months and events
with smaller maximum amplification. For fixed separation it increases
for binaries with more extreme mass ratios.<br><br>
Problem of degeneracy in photometric light curve solution between
binary lens and binary source microlensing events was studied on simulated
data, and data observed by the PLANET collaboration. The fitting code
BISCO using the PIKAIA genetic algorithm optimizing routine was written
for optimizing binary-source microlensing light curves observed at
different sites, in I, R and V photometric bands. Tests on simulated
microlensing light curves show that BISCO is successful in finding
the solution to a binary-source event in a very wide parameter space.
Flux ratio method is suggested in this work for breaking degeneracy
between binary-lens and binary-source photometric light curves. Models
show that only a few additional data points in photometric V band,
together with a full light curve in I band, will enable breaking the
degeneracy. Very good data quality and dense data sampling, combined
with accurate binary lens and binary source modeling, yielded the
discovery of the lowest-mass planet discovered outside of the Solar
System so far, OGLE-2005-BLG-390Lb, having only 5.5 Earth masses.
This was the first observed microlensing event in which the degeneracy
between a planetary binary-lens and an extreme flux ratio binary-source
model has been successfully broken. For events OGLE-2003-BLG-222 and
OGLE-2004-BLG-347, the degeneracy was encountered despite of very
dense data sampling. From light curve modeling and stellar evolution
theory, there was a slight preference to explain OGLE-2003-BLG-222
as a binary source event, and OGLE-2004-BLG-347 as a binary lens event.
However, without spectra, this degeneracy cannot be fully broken.<br><br>
No planet was found so far around a white dwarf, though it is believed
that Jovian planets should survive the late stages of stellar evolution,
and that white dwarfs will retain planetary systems in wide orbits.
We want to perform high precision astrometric observations of nearby
white dwarfs in wide binary systems with red dwarfs in order to find
planets around white dwarfs. We selected a sample of observing targets
(WD-RD binary systems, not published yet), which can possibly have
planets around the WD component, and modeled synthetic astrometric
orbits which can be observed for these targets using existing and
future astrometric facilities. Modeling was performed for the astrometric
accuracy of 0.01, 0.1, and 1.0 mas, separation between WD and planet
of 3 and 5 A.U., binary system separation of 30 A.U., planet masses
of 10 Earth masses, 1 and 10 Jupiter masses, WD mass of 0.5M
and 1.0 Solar masses, and distances to the system of 10, 20 and 30
pc. It was found that the PRIMA facility at the VLTI will be able
to detect planets around white dwarfs once it is operating, by measuring
the astrometric wobble of the WD due to a planet companion, down to
1 Jupiter mass. We show for the simulated observations that it is
possible to model the orbits and find the parameters describing the
potential planetary systems. / Bei von Sternen verursachten Mikrolinsen-Ereignissen beobachtet man
meist symmetrische Lichtkurven einer einzelnen Linse oder asymmetrische
Lichtkurven (oftmals mit Kaustik-Crossing), die durch Doppel-Linsen
hervorgerufen werden. Im Prinzip kann aus der Zahl der gemessenen
unsymmetrischen Ereignisse der Anteil der Doppelstern-Systeme in Abhängigkeit
vom Winkelabstand abgeschätzt werden. Allerdings kann auch ein
Doppelsystem Lichtkurven erzeugen, die gut mit einer Einzellinsen-Lichtkurve
gefittet werden können. Die gilt insbesondere bei lückenhafter
Messung oder grossen Messfehlern. In dieser Arbeit wird für
verschiedene Beobachtungsbedingungen untersucht, wie häufig Lichtkurven,
die von Doppellinsen mit unterschiedlichen Abständen erzeugt
werden, gut mit Einzellinsen-Lichtkurven gefittet werden können
und damit fehlinterpretiert werden. Es wurde herausgefunden, dass der
Anteil fehlinterpretierter Lichtkurven stark von der Separation der
Komponenten abhängig ist: das Minimum liegt zwischen 2 A.E. and
5 A.E. / wobei der Anteil immer noch 5% beträgt. Die Rate der Fehlinterpretationen
ist höher für kurze Mikrolinsen-Ereignisse (bis zu wenigen
Monaten) und für Ereignisse mit geringer Maximalverstärkung.
Bei gleicher Separation steigt die Rate mit extremeren Massenverhältnissen
an.<br><br>
Das Problem der Degenerierung zwischen den Lichtkurven für doppelte
Linsensysteme und doppelte Hintergrund-Quellen wurde anhand simulierter
Daten und mit Beobachtungsdaten des PLANET Projekts untersucht. Der
Fit-Code BISCO, der den genetischen Algorithmus PIKAIA nutzt, wurde
geschrieben, um Doppel-Linsen Lichtkurven, die von verschiedenen Observatorien
in den photometrischen Bändern I, B, und V gemessen wurden, zu
modellieren. Tests mit simulierten Daten haben gezeigt, dass BISCO
in der Lage ist, in einem sehr weiten Parameterbereich die korrekte
Lösung für die Lichtkurve einer Doppel-Linsen zu finden.
In dieser Arbeit wird die Flussverhältnis-Methode empfohlen,
um die Degenerierung zwischen Doppel-Linse und Doppel-Quelle aufzulösen.
Modellierungen zeigen, dass nur wenige zusätzliche Datenpunkte
im V-Band genügen, um zusammen mit einer vollständigen Lichtkurve
im I-Band die Degenerierung aufzubrechen. Mit sehr guter Datenqualität
und zeitlich dichten Messungen, kombiniert mit genauer Modellierung
von Doppel-Linsen und Doppel-Quellen, gelang die Entdeckung des bisher
masseärmsten Planeten ausserhalb des Sonnensystems: OGLE-2005-BLG-390Lb,
mit nur 5.5 Erdmassen. Dies war das erste Mikrolinsen-Ereignis, bei
dem die Degenerierung zwischen plantarer Doppel-Linse und einer Doppel-Quelle
mit extremem Flussverhältnis erfolgreich aufgelöst wurde.
Für die Ereignisse OGLE-2003-BLG-222 und OGLE-2004-BLG-347 besteht
die Degenerierung trotz sehr dichter Messungen. Aufgrund der Lichtkurvenmodellierung
und Argumenten aus der Theorie der Sternentwicklung ist die Erklärung
von OGLE-2003-BLG-222 als Doppel-Quelle und OGLE-2004-BLG-347 als
Doppel-Linsen Ereignis vorzuziehen. Allerdings kann die Degenerierung
ohne spektrale Daten nicht vollständig aufgelöst werden.<br><br>
Bisher wurde kein Planet als Begleiter eines Weissen Zwerges gefunden,
obwohl es möglich sein sollte, dass jupiterähnliche
Planeten die Spätstadien der Sternentwicklung überleben
und dass sich Weisse Zwerge Planetensysteme mit weiten Umlaufbahnen
erhalten können. Wir planen hochgenaue astrometrische Beobachtungen
von nahen Weissen Zwergen in weiten Doppelsystemen, um Planeten um
Weisse Zwerge zu finden. Wir haben eine Stichprobe von Systemen zusammengestellt, in denen möglicherweise Planeten gefunden werden könnten.
Wir haben synthetische astrometrische Orbits modelliert, die für
diese Systeme mit existierenden und zukünftigen astrometrischen
Instrumenten beobachtbar sind. Die Modellierungen wurden für
astrometrische Genauigkeiten von 0.01, 0.1, 1.0 Mikrobogensekunden
gerechnet. Als Abstände zwischen weissem Zwerg und Planet wurden
3, 5 und 10 Astronomische Einheiten angenommen, für den Abstand
zwischen den Doppelsternkomponenten 30 A.E. Als Planetenmassen wurden
10 Erdmassen, bzw. 1 und 10 Jupitermassen gewählt, als Masse
für den weissen Zwerg 0.5 und 1.0 Sonnenmassen. Die
Distanzen zum System betragen 10 und 20 parsec. Als Resultat dieser
Untersuchung wurde herausgefunden, dass das PRIMA Instrument am VLTI
in der Lage sein wird, die astrometrischen Oszillationen, die ein
Planet ab einer Jupitermasse verursacht, zu detektieren. Wir zeigen,
dass es möglich sein wird, die Umlaufbahnen solcher Planeten
zu modellieren und damit die Parameter dieser Planetensysteme zu bestimmen.
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A Study of Jupiter TrojansKarlsson, Ola January 2012 (has links)
Jupiter Trojan asteroid dynamics have been studied for a long time but it is only within the last decades that the known population has become large enough to make other studies meaningful. In four articles I have been scratching the surface of the unknown Trojan knowledge space. Paper I presents photometric observations confirming a larger variety in surface redness for the smaller Trojans compared to the larger ones, in line with the groups in the outer main asteroid belt. However, the largest Trojans are significantly redder compared to the largest Cybele and Hilda asteroids. Paper II is an investigation of the Trojan discovery completeness. The analysis shows that all Trojans down to a limiting absolute magnitude of H=11.5 mag have been discovered. Missing Trojans in the almost discovery-completed section should have inclinations above the mean of the same group. The faintest Trojans are discovery biased due to orbit orientations similar to the Milky Way. Paper III is a general review of dynamical and physical properties of the discovery-completed sample of Jupiter Trojans found in Paper II. The two Trojan swarms are often treated as being equal, but are different in a number of details. Two known facts are that the L5 swarm is less rich, while the L4 swarm has a larger fraction of low inclination Trojans. Trojans are in general red objects but the mean redness is higher for Trojans which have not collided compared to Trojans in families. Paper IIII is an investigation of Trojan collisions, family detection and evolution. Collision circumstances were mapped using numerical simulations and recorded Trojan close approaches. Synthetic families were created and evolved numerically. The result suggests that the HCM family detection technique can find Trojan families even in a densely populated parameter space. However, interlopers cannot be avoided at any level but their contribution should be less than 30%. Synthetic families can be identified with backwards orbital integrations for times up to a Gyr-scale. However, there are discrepancies between real Trojan families and my synthetic families.
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Survival of prebiotic compounds during exogenous delivery : implications for the origin of life on earth and potentially on mars /Glavin, Daniel Patrick. January 2001 (has links)
Thesis (Ph. D.)--University of California, San Diego, 2001. / Vita. Includes bibliographical references.
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Climate modeling of giant planets : the Saturnian seasonal stratosphereStrong, Shadrian Brittany, 1980- 02 October 2012 (has links)
Not available / text
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Structure and evolution of circumstellar disks, a Spitzer viewCieza-Gonzalez, Lucas Alejo, 1978- 28 August 2008 (has links)
This dissertation is the sum of five studies of the structure and evolution of circumstellar disks, the birthplace of planets. These studies are all based on Infrared data from the Spitzer Space Telescope, and taken together trace the evolution of disks from the optically thick primordial stage to the optically thin debris disk stage. The five projects included in this dissertation are diverse but they are all interconnected and have a common underlying motivation: to impose observational constraints on different aspects of planet formation theories. In the first project, we study the near and mid-IR (1.2-24 [mu]m) emission of Classical T Tauri Star (CTTS), which are low-mass pre-main sequence (PMS) stars that show clear evidence for accretion. We discuss the implications of our results on the structure of their inner disks and their estimated ages. In the second project, we study the incidence as a function of age of disks around weak-line T Tauri stars (low-mass PMS stars that are mostly coeval with CTTS but that do not show clear evidence for accretion) and explore the structure of these disks. We estimate the dissipation timescale of the planet-forming region of primordial disks and discuss the implications for planet formation theories. The third and fourth projects deal with the evolution of angular momentum of PMS stars. We search for observational evidence for the connection between stellar rotation and the presence of a disk predicted by the current disk-braking paradigm, according to which the rotational evolution of PMS stars is regulated through magnetic interactions between the stellar magnetosphere and the inner disk. The last project deals with debris disks, which are second-generation disks where the dust is continuously replenished by collisions between planetesimals. We search for debris disks in the far-IR (24-160 [mu]m) around a sample of Hyades Cluster members. We discuss the implications of our results on the evolution of debris disks and on the Late Heavy Bombardment in the Solar System. / text
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