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 21 for “"pre-main-sequence"”.
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Lithium and age of pre-main sequence stars
… sulla base della dinamica, quindi senza precedenti ipotesi. La medesima metallicità e età delle componenti di un sistema binario rappresenta un forte vincolo nella determinazione delle soluzioni. In una prima fase ho svolto una campagna spettroscopica allo scopo di ottenere dati …
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Infrared excesses from accretion streams in pre-main-sequence binaries
… study of very close binary systems, because its presence is a sign of stream accretion. There is a periodicity in this variation, with a period equal to the binary period. The general pattern the excess follows is that it is larger at the periastron of the orbit. We also examined the role of the …
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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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Magnetic Coupling between a “Hot Jupiter” Extrasolar Planet and Its Pre-Main-Sequence Central Star
… of extrasolar planets, the magnetic torque of a pre-main-sequence central star on a single orbiting "hot Jupiter" planet is calculated. The star's magnetic field is modeled as a dipole magnetic field. The time-dependent stellar radius is calculated for four different stellar mass sizes; …
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A detailed infrared study of the star forming region NGC2071 IRS
This thesis presents measurements made at infrared (IR) wavelengths of the bipolar outflow in NGC2071. The observing methods at these wavelengths, the results of these data, and the nature of this outflow are discussed. The first JHK and NBL high spatial resolution images of the NGC2071IR region …
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Optical spectroscopic studies of two star forming regions
… in Serpens have been identified based on the presence of Hα in emission, lithium absorption, X-ray emission, a mid-infrared excess, and/or reflection nebulosity. Effective temperatures and bolometric luminosities were compared with theoretical tracks and isochrones for pre-main-sequence stars …
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Analysis of Molecular Variability Due to Accretion Bursts in the Protoplanetary Disk of Ex Lup as Observed with the James Webb Space Telescope
… disks are structures that form around a pre-main sequence star as a result of conservation of angular momentum during collapse of dense cores in star-forming regions. They accrete gas onto the central proto-star, and are the sites of planet formation. Early in their lifetime, disk …
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The Formation Of Massive Stars: A 30 Mo Case Study
… a convective core throughout the whole of their pre-main sequence phase.;Pre-main sequence evolution has been calculated under the accretion paradigm: beginning with a collapsed core, mass is accreted until a final stellar mass is reached. The calculations begin with a one solar mass core.;The …
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Spectroscopic and spectro-astrometric analysis of T Tauri Stars
… T Tauri stars. These objects are low-mass, pre-main sequence stars surrounded by circumstellar disks of material from which planets are believed to form. We present high-resolution, near-infrared spectroscopic data for the T Tauri stars DR Tau and AA Tau using NIRSPEC at the Keck II …
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High-resolution studies of protoplanetary disks
This work presents a multi-wavelength search (near-IR, mid-IR, mm) for previously unknown circumstellar disks and a study of those disk candidate objects which are not yet well characterised in the literature. 22 candidate stars, most of these constituting known exoplanet systems, were examined for …
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Photometric monitoring of early type emission line stars
… emphasis is placed on observations of suspected pre-main-sequence objects such as Herbig Ae/Be stars. The observations, together with data from the IRAS point source catalogue, are analysed to probe the circumstellar environments of these objects and to determine the extent and causes of optical …
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Development of an H-Alpha Index for the Detection of PMS Candidates in Young Open Clusters
… is the optically visible phase known as the pre-main-sequence or PMS phase. In order to further the understanding of this phase, more of these PMS objects need to be identified and classified. Previous techniques have used photometry to identify possible PMS objects by their characteristic Hα …
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Flare stars in the solar vicinity
… T Tauri phase with a disk and the zero-age main sequence can be provided by the catalog of flare stars and related objects compiled by Gershberg et al. (1999) because young stars are often variable and exhibit large eruptions (flares). In a first step we need to verify that these stars are …
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Dust in circumstellar disks
This thesis presents observational and theoretical studies of the size and spatial distribution of dust particles in circumstellar disks. Using millimetre interferometric observations of optically thick disks around T Tauri stars, I provide conclusive evidence for the presence of millimetre- to …
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A technique for astronomical spectroscopy with a multi-aperture telescope
… its manipulation, display and storage presented a major research effort which were largely overcome by the use of cheap, digital micro-computers. To achieve rapid and flexible data handling the i.E.E.E. bus was used as the communication medium between control and data collecting …
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The Inner Gaseous Disks Of Herbig Be Stars
… Ae/Be stars are intermediate mass (~2 to 20Msun) pre-main sequence stars that inherit a circumstellar disk of dust and gas from their formation phase. The region of this disk closest to the star is entirely gaseous because dust evaporates at the high temperatures there, and this gaseous region is …
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Constraining Stellar Evolution in Young Open Clusters with NGTS
… is fundamental to astronomy, yet there remain significant gaps in our knowledge. Scientific progress requires testing our best explanations against observation, and open clusters act as key test sites for theories of stellar evolution. Observations of young open clusters enable theoretical …
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Angular Momentum Evolution of Young Stars
This thesis presents a detailed 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 …
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The Galactic Starburst Region NGC 3603 : exciting new insights on the formation of high mass stars
… to the formation of high mass stars still remain a mystery. There is no doubt that low mass stars like our Sun form via accretion of gas and dust from their natal environment. With respect to the formation of high mass stars theorists currently discuss two possible scenarios controversely: …
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Probing planetary disks: from birth to protoplanets
… them. While the exact details of the process remain a large area of research, it is the gas and dust in these disks that will grow into planets. By the Class II phase of a protostar’s evolution, large disks are common (so there is a large mass reservoir available) and it is commonly assumed that …
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