Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 29 for “"young stars"”.
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Angular Momentum Evolution of Young Stars
… investigation of the rotational behaviour of young pre-main sequence (PMS) stars in order to achieve a better understanding of their angular momentum evolution during this evolutionary stage. For that purpose I have carried out an extensive photometric monitoring program which enabled me to …
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Exploring the Environment of Young Stars: Disks, Companions and Clusters
… FU Ori phenomenon and the formation of massive stars. The main results are the following: 1. By applying the novel method of polarimetric differential imaging and the NACO/VLT instrument we probe one of the closest circumstellar disks in the planet-forming age at scales of our inner Solar …
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An unbiased infrared H2 search for embedded flows from young stars in Orion A
Gasausströmungen, oft in der Form hoch kollimierter Jets, sind ein allgegenwärtiges Phänomen bei der Geburt neuer Sterne. Emission von stossangeregtem molekularem Wasserstoff bei Wellenlängen im nahen Infrarotbereich ist ein Merkmal ihrer Existenz und auch in eingebetteten, im Optischen …
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Constraining the Initial Conditions and Final Outcomes of Accretion Processes around Young Stars and Supermassive Black Holes
… I discuss probes of small spatial scales around young stars and protostars and around the supermassive black hole at the galactic center. I begin by describing adaptive optics-fed infrared spectroscopic studies of nascent and newborn binary systems. Binary star formation is a significant mode of …
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Coronal properties of pre-main sequence stars in the Orion Trapezium Cluster
Most of the young stars in the Orion Trapezium Cluster are much more peculiar in X-rays than expected, considering their structure, environment, and age. Highly resolved X-ray spectra provide many more details in order to study these peculiarities, specifically with respect to abundances and …
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Rotation Period Distributions and Light Curve Morphologies of Low Mass Stars and Young Associations
… centered around the rotation periods of low-mass stars and association of young stars. Rotation periods are a link to the age of the star, as they lose angular momentum over time. To understand how this angular momentum evolves requires understanding the rotation period distributions of a range of …
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High-resolution spectroscopy of very active solar-type stars
… spectroscopy has been used to find stars with highly active chromospheres within 50 pc of the Sun for the Northern hemisphere. We have analyzed thirteen such stars, using high-resolution spectroscopy, to determine Lithium abundances and metallicities. Although two of these stars may …
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Flare stars in the solar vicinity
Young stars close to the sun (within 100 pc) yield an interesting sample in many respects: They are relatively bright and because of their close distance we can resolve the surroundings of these stars by using adaptive optics on 8 to 10 m class telescopes (e.g. VLT or Keck). In the K-band the …
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Protoplanetary disc evolution and dispersal
In this thesis I have studied how discs around young stars evolve and disperse. In particular, I build models which combine viscous evolution with photoevaporation, as previous work suggests that photoevaporation can reproduce the observed disc evolution and dispersal time-scales. The main question …
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Optical spectroscopic studies of two star forming regions
… The goals of this study were to identify young stellar objects (YSOs) and estimate ages and masses in order to infer an initial mass function (IMF), investigate disk evolution, and determine the star-forming history. Optical spectroscopic surveys of an unbiased sample of candidate young …
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Understanding the Star -Forming Environment in Stellar Clusters
… formation of low-mass cluster members. Embedded, young, and intermediate-mass stellar clusters around Herbig Ae/Be stars are sampled. Mid- and near-infrared observations identifying young stars and millimeter interferometric observations probing dense molecular gas and dust continuum are …
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High-Resolution Imaging of Dense Gas Structure and Kinematics in Nearby Molecular Clouds with the CARMA Large Area Star Formation Survey
… for how clouds form structures which evolve into young cores and stars. Previous observations show the general turbulent and hierarchical nature of clouds. However, current understanding of the star formation pathway is limited by existing data that do not combine angular resolution needed to …
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Chromospheric activity and lithium abundance in the NGC2516 and NGC3766 open clusters
… activity and lithium abundance of late type stars in open clusters of different ages. The study of open cluster is very important for our understanding of stellar evolution and atmospheres, since all cluster members have almost the same age and chemical composition and this allows to infer …
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Spectro-astrometry as a Tool for Detecting Planets in Transitional Disks
… population of extra solar planets orbiting stars of many different sizes and temperatures. It is much easier to detect a large planet that orbits close to its star as opposed to a smaller, more distant one. This led to the discovery of many Hot-Jupiters in the initial stages of exoplanet …
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Probing giant-planet forming zones around Solar-like stars with CO
Protoplanetary disks are dusty disks around young stars where planets are formed. The evolution and composition of protoplanetary disks determine the time, environments and materials available for planet formation. However fundamental properties of protoplanetary disks such as mass, composition, …
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Investigating the role of ionised outflows in galactic evolution through spatially resolved spectroscopy
… excitation must come from UV radiation due to stars in the outflow and not stars in the galactic disk. Finally, I trace kinematical fingerprints of young stars blueshifted relative to those in the galactic disk. The second part of this thesis focuses upon expanding the study of star formation …
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Aktyvaus branduolio tėkmės įtaka juodosios skylės maitinimui /
… potentially contributing to the formation of new stars. According to observations by various teams of astronomers, young stars orbiting in eccentric elliptical rings have been found in the very nearest regions, a few parsecs in size, near the SMBH at the center of the Galaxy. This study aims to …
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High-resolution studies of exoplanetesimal belt formation and evolution
Stars are born with gas-rich protoplanetary discs that typically survive for a few Myr before dispersing, after which they are left with the planetary bodies that formed within the protoplanetary system: planets, and belts of planetesimals (km-sized rocky and icy bodies). Planetesimals within belts …
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Turbulent Angular Momentum Transport in Weakly-Ionized Accretion Disks
… magnetic field. Many disks, such as disks around young stars and disks in binary systems that are in quiescence, are too cold to be sufficiently ionized, and so efforts to establish the presence of turbulence in these disks continues. This dissertation focuses on several possible mechanisms for …
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