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  • Wechselwirkung des Mars mit dem Sonnenwind
    1 Dateiname Boesswetter2009 pdf PDF 15 2 MB Google View Download Kategorien Solar terrestrische Erscheinungen Astronomie Marsatmosphäre Astronomie Zur Langanzeige Zusammenfassung Seit den 60er Jahren des letzten Jahrhunderts ist Mars immer wieder das Ziel von Raumfahrtmissionen gewesen um unter anderem nach Wasser auf unserem Nachbarplaneten zu suchen Nachdem die bisher analysierten Oberflächenmerkmale auf ein Vorhandensein von flüssigem Wasser beim Entstehen der Oberfläche deuten wurde im Juni 2008 von der Sonde Phoenix erstmals Wassereis unter der Oberfläche direkt nachgewiesen In dieser Arbeit wird untersucht wieviel Wasser Mars in den vergangenen 4 5 Milliarden Jahren verloren hat und welche Mechanismen dabei eine Rolle gespielt haben Bei den nichtthermischen Mechanismen hat insbesondere die Umströmung des Sonnenwindplasmas um die Marsatmosphäre mittels seiner elektromagnetischen Felder entscheidenden Einfluß auf den Verlust planetarer Sauerstoff und Wasserstoffionen Dieses Wechselwirkungsszenario wurde mit numerischen Plasmasimulationen untersucht Das verwendete Hybrid Modell erfasst vollständig die Ionendynamik durch eine kinetische Beschreibung der Ionen Die Elektronen werden als massenlose Flüssigkeit modeliert Eine Reihe von Ergebnissen wird vorgestellt a In Übereinstimmung mit dem ASPERA 3 Experiment auf Mars Express werden zwei Plasmagrenzschichten und zwar der Bow Shock und die Ion Composition Boundary 34 identifiziert b Es wird gezeigt dass beim Vorbeiflug der Raumsonde Rosetta eine

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-3097-1 (2016-02-15)
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  • Multi-telescope studies of neutron stars
    pdf PDF 10 7 MB Google View Download Kategorien Pulsare Neutronensterne Astronomie Spektren und Spektroskopie von Sternen Astronomie Radioastronomie Zur Langanzeige Zusammenfassung Neutron stars are unique stellar remnants with extreme properties as their density and magnetic field Their study can be the key to a number of unanswered problems in fundamental physics and astronomy ranging from stellar evolution to strong field gravity One of the best ways of studying these objects is with observations at radio wavelengths the efficiency of which can be vastly improved with the combination of data from multiple radiotelescopes In this thesis we use the largest European radiotelescopes for performing high quality studies of the properties of objects belonging into two separate categories of neutron stars millisecond pulsars and magnetars In the first part of this thesis a complete description of the observing systems and calibration procedures for the multiple telescopes used is presented Specifically all observations were made with the European Pulsar Timing Array EPTA telescopes which are the Effelsberg 100m radiotelescope in Germany the Lovell 76m radiotelescope in UK the Westerbork 94m equivalent synthesis radiotelescope in the Netherlands and the Nanc cay 94m equivalent decimetric radiotelescope in France Zsfassung in dt und engl Sprache

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-3091-D (2016-02-15)
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  • Star-disc encounters in young star clusters
    309F 2 Dateiname Olczak2009 pdf PDF 1 8 MB Google View Download Kategorien Extrasolare Planetensysteme Astronomie Sterne Sternhaufen Astronomie Zur Langanzeige Zusammenfassung According to current knowledge star formation occurs preferentially in clustered environments As a byproduct of the star formation process young stars are found to be surrounded by accretion discs that are potential birth places of planets and planetary systems Located in the hosting cluster these protoplanetary discs are potentially subject to stellar interactions These interactions give rise to a fundamental question of clustered star formation How far does the cluster environment affect the evolution of protoplanetary discs and the formation of planets The question is addressed in the present investigation in terms of the effect of stellar encounters on stars and their disc in young clusters by combining numerical simulations of isolated star disc encounters and stellar dynamics of young star clusters The investigation is composed of three key aspects First simulations of a dynamical model of the Orion Nebula Cluster ONC show that disc destruction is dominated by encounters with high mass stars that act as gravitational foci for the lower mass stars in the cluster centre The massive stars are thus subject to repeated encounters which

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-309F-2 (2016-02-15)
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  • Supernova-driven turbulence and magnetic field amplification in disk galaxies
    http hdl handle net 11858 00 1735 0000 0001 30A0 B Dateiname Gressel2009 pdf PDF 21 3 MB Google View Download Kategorien Elektrische und magnetische Felder Sterne Supernovae Astronomie Zur Langanzeige Zusammenfassung Supernovae are known to be the dominant energy source for driving turbulence in the interstellar medium Yet their effect on magnetic field amplification in spiral galaxies is still poorly understood Analytical models based on the uncorrelated ensemble approach predicted that any created field will be expelled from the disk before a significant amplification can occur By means of direct simulations of supernova driven turbulence we demonstrate that this is not the case Accounting for vertical stratification and galactic differential rotation we find an exponential amplification of the mean field on timescales of 100Myr The self consistent numerical verification of such a fast dynamo is highly beneficial in explaining the observed strong magnetic fields in young galaxies We furthermore highlight the importance of rotation in the generation of helicity by showing that a similar mechanism based on Cartesian shear does not lead to a sustained amplification of the mean magnetic field This finding impressively confirms the classical picture of a dynamo based on cyclonic turbulence Share on Das Dokument

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-30A0-B (2016-02-15)
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  • Characterization of the stellar variability in CoRoT fields with BEST telescopes
    Google View Download Kategorien Detektionsmethoden Astronomie Extrasolare Planetensysteme Einzelne Weltraumprojekte Bodenständige UV Optische und Infrarotteleskope Astronomische Instrumente Zur Langanzeige Zusammenfassung The first extrasolar planet 51 Peg b around the G type star has been reported in 1995 The planet with few Jupiter masses orbiting its star very closely was detected by measurement of the oscillation in the radial velocity of the host star In 1999 the first transit when the planet is eclipsing the host star of the extrasolar planet HD209458 b was observed with a small ground based photometric telescope Ever since new planets in distant systems are continuously being detected with new high precision instruments from the ground and from space The department of Extrasolar Planets and Atmospheres at Deutsches Zentrum für Luft und Raumfahrt Berlin DLR is involved in the detection and characterization of extrasolar planets through participation in the CoRoT space mission Furthermore two ground based photometric telescope systems are operated as a ground based support for the space mission CoRoT dedicated to asteroseismology and to extrasolar planet search with the help of the transit method The BEST project consists of two small aperture wide field of view photometric telescopes devoted to the search for transiting

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-3095-5 (2016-02-15)
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  • Zeeman-Doppler Imaging of active late-type stars
    00 1735 0000 0001 3090 F Dateiname Kopf2009 pdf PDF 3 5 MB Google View Download Kategorien Elektrische und magnetische Felder Sterne Kosmogonie Astronomie Zur Langanzeige Zusammenfassung Stellar magnetic fields as a crucial component of star formation and evolution evade direct observation at least with current and near future instruments However investigating whether magnetic fields are generated by a dynamo process or represent relics from the formation process or whether they show a behavior similar to the sun or something very different it is essential to investigate their structure and temporal evolution Fortunately nature provides us with the possibility to indirectly observe surface topologies on distant stars by means of Doppler shift and polarization of light though not without its challenges Based on the mentioned effects the so called Zeeman Doppler Imaging technique is a powerful method to retrieve magnetic fields from rapid rotating stars based on measurements of spectropolarimetric observations in terms of Stokes profiles In recent years a large number of stellar magnetic field distributions could be reconstructed by Zeeman Doppler Imaging ZDI However the implementation of this method often relies on many approximations because as an inversion method it entails enormous computational requirements Share on Das Dokument

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-3090-F (2016-02-15)
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  • Massive stars in the Galactic Center Quintuplet cluster
    of the Galactic center Quintuplet cluster the spectral analysis of the cluster Wolf Rayet stars of the nitrogen sequence to determine their fundamental stellar parameters and discusses the obtained results in a general context The Quintuplet cluster was discovered in one of the first infrared surveys of the Galactic center region Okuda et al 1987 1989 and was observed for this project with the ESO VLT near infrared integral field

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-3092-B (2016-02-15)
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  • Explorative approach to the dust evolution in binary star systems
    Zur Langanzeige Zusammenfassung This thesis discusses dust formation in binary systems in particular for binary systems consisting of a Mira like star and a brown dwarf A Mira like star is an intermediate mass star in a late stage of their stellar evolution on the Asymptotic Giant Branch AGB and a brown dwarf is a sub stellar object with a mass below that necessary to maintain hydrogen burning nuclear fusion reactions in their cores In their radial pulsating elevated convective atmospheres Mira stars often develop strong stellar winds which are driven by radiation pressure on the dust and lead to a substantial mass loss of the star Stellar winds are of central importance for the development of medium heavy AGB stars Also they are a reliable source for the production of dust particles and heavy elements for the interstellar medium and the chemical evolution of galaxies In fact most stars are in binary or multiple star systems For a complete description of the processes of dust formation in binary star systems it is necessary to study the perturbative influence of a second star in the vicinity of a AGB star with a strong stellar wind This endeavour is embedded in

    Original URL path: http://e-docs.geo-leo.de/handle/11858/00-1735-0000-0001-309D-6 (2016-02-15)
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