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  • Other Sources  (37)
  • 523  (37)
  • Univ. Potsdam  (22)
  • Univ. Berlin  (15)
  • English  (31)
  • German  (6)
  • Chinese
  • Greek, Modern (1453- )
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  • Russian
  • 2020-2023
  • 2010-2014  (37)
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  • Other Sources  (37)
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  • English  (31)
  • German  (6)
  • Chinese
  • Greek, Modern (1453- )
  • Portuguese
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  • 2020-2023
  • 2010-2014  (37)
Year
  • 1
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    Hydrogen-deficient central stars of planetary nebulae (2010)
    Univ. Potsdam
    Details
    Publication Date: 2020-10-07
    Description: 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.
    Description: thesis
    Keywords: 523 ; TEG 000 ; Kosmogonie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 102 S.
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  • 2
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    Massive stars in the Galactic Center Quintuplet cluster (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: The presented thesis describes the observations 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 instrument SINFONI-SPIFFI. The subsequent data reduction was performed in parts with a self-written pipeline to obtain flux-calibrated spectra of all objects detected in the imaged field of view ...
    Description: thesis
    Keywords: 523 ; TIC 000 ; THT 800 ; TIE 662 ; Sternhaufen {Astronomie} ; Massenreiche Sterne {Astronomie} ; Struktur der Milchstrasse {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 115 S.
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  • 3
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    Zeeman-Doppler Imaging of active late-type stars (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: 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.
    Description: thesis
    Keywords: 523 ; THR 000 ; TEG 000 ; Elektrische und magnetische Felder {Sterne} ; Kosmogonie {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 107 S.
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  • 4
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    Radiative transfer in the exosphere of Saturn's moon Titan (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: This work focuses on the distribution of atomic hydrogen in the exosphere of Saturns̉ moon Titan. This work is based on measurements performed by the Hydrogen Deuterium Absorption Cell (HDAC) aboard the Cassini spacecraft, that should directly determine the D/H ratio from the UV emission of atomic hydrogen and deuterium at 121.567 and 121.533 nm, respectively. HDAC measurements were performed on December 26, 2005 during the ninth Titan flyby of the Cassini orbiter. Unfortunately the amount of deuterium in the absorption cell could not be determined. Thus, the purpose, HDAC was designed for could not be achieved. For this reason, HDAC has performed measurements only once. However, the amount of atomic hydrogen in the absorption cell is well known, hence the data using only the hydrogen cell can be used in order to investigate Titans̉ exosphere. This work aims at simulating the HDAC measurements performed in order to investigate Titan’s exosphere, e.g. to determine the distribution of atomic hydrogen. A model of Titan’s exosphere including atomic hydrogen and methane has been developed and the transfer of solar radiation is calculated in order to simulate the HDAC measurements. The radiative transfer is solved using the Monte Carlo method. For the exospheric model, two different atomic hydrogen density distributions were applied, which determine the distribution in the exosphere by different approaches. Density profiles calculated by both models mainly differ in the lower exosphere ...
    Description: thesis
    Keywords: 523 ; TGG 655 ; Saturnmonde {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 171 S.
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  • 5
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    Constraining the UV background with the proximity effect (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: After the epoch of reionisation the intergalactic medium (IGM) is kept at a high photoionisation level by the cosmic UV background radiation field. Primarily composed of the integrated contribution of quasars and young star forming galaxies, its intensity is subject to spatial and temporal fluctuations. In particular in the vicinity of luminous quasars, the UV radiation intensity grows by several orders of magnitude. Due to an enhanced UV radiation up to a few Mpc from the quasar, the ionised hydrogen fraction significantly increases and becomes visible as a reduced level of absorption in the HI Lyman alpha (Ly-alpha) forest. This phenomenon is known as the proximity effect and it is the main focus of this thesis ...
    Description: thesis
    Keywords: 523 ; TBI 000 ; Ultraviolett-Astronomie
    Language: German
    Type: monograph , publishedVersion
    Format: 94 S.
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  • 6
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    Explorative approach to the dust evolution in binary star systems (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: 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 a long standing tradition of scientific investigation of dust formation at the Zentrum für Astronomie und Astrophysik (ZAA) at the Technical University of Berlin...
    Description: thesis
    Keywords: 523 ; THT 900 ; TII 900 ; Doppelsterne {Astronomie} ; Interstellarer Staub {Astronomie: Interstellare Materie}
    Language: English
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  • 7
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    Characterization of the stellar variability in CoRoT fields with BEST telescopes (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: 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 Jupiter-sized extrasolar planets and to the characterization of variable stars in CoRoT target fields...
    Description: thesis
    Keywords: 523 ; THX 100 ; TJ 900 ; TCE 220 ; Detektionsmethoden {Astronomie: Extrasolare Planetensysteme} ; Einzelne Weltraumprojekte ; Bodenständige UV-, Optische und Infrarotteleskope {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
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  • 8
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    Supernova-driven turbulence and magnetic field amplification in disk galaxies (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: 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 ...
    Description: thesis
    Keywords: 523 ; THR 000 ; THU 162 ; Elektrische und magnetische Felder {Sterne} ; Supernovae {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 109 S.
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  • 9
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    Electron acceleration in a flare plasma via coronal circuits (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: The Sun is a star, which due to its proximity has a tremendous influence on Earth. Since its very first days mankind tried to "understand the Sun", and especially in the 20th century science has uncovered many of the Sun's secrets by using high resolution observations and describing the Sun by means of models. As an active star the Sun's activity, as expressed in its magnetic cycle, is closely related to the sunspot numbers. Flares play a special role, because they release large energies on very short time scales. They are correlated with enhanced electromagnetic emissions all over the spectrum. Furthermore, flares are sources of energetic particles. Hard X-ray observations (e.g., by NASA's RHESSI spacecraft) reveal that a large fraction of the energy released during a flare is transferred into the kinetic energy of electrons. However the mechanism that accelerates a large number of electrons to high energies (beyond 20 keV) within fractions of a second is not understood yet.
    Description: thesis
    Keywords: 523 ; TGC 560 ; TGC 440 ; Eruptionen, Flares {Astronomie: Sonne} ; Korpuskelstrahlung {Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 122 S.
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  • 10
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    Search for neutrino induced cascades with 5 years of the AMANDA-II data (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: Das Antarctic Muon And Neutrino Detector Array (AMANDA) ist ein Cherenkov Detektor, der sich im Gletscher der Antarktis am Südpol befindet. Wir präsentieren die Analyse von Daten, die in den Jahren 2000 bis 2004 gesammelt wurden, die einer effektiven Detektorlaufzeit von 1001 Tagen entsprechen. Die Suche zielt auf den Nachweis von elektomagnetische und hadronische Teilchenschauern, so gennante Kaskaden, die durch Elektron- und Tauneutrinowechselwirkung produziert werden können. Die hadronischen Kaskaden können auch über neutrale Ströme Wechselwirkung von Neutrinos aller Arten produziert werden. Der Kaskadenkanal hat einige Vorteile in der Suche nach einem diffusen Fluss von astrophysikalischen Neutrinos. Durch die gute Energieauflösung des AMANDA Detektors kann man zwischen einem harten astrophysikalische Spektrum und einem weichen atmosphärischen Spektrum unterscheiden. Außerdem ist der atmosphärischen Elektronneutrinos Fluss um eine Gößenordnung kleiner als der atmosphärische Myonneutrinofluss. Der Untergrund von atmosphärischem Myonen aus Luftschauern kann unterdrückt werden, weil diese als Spuren im Detektor erscheinen und leicht zu identifizieren sind...
    Description: thesis
    Keywords: 539.7215 ; 523 ; 550 ; TBN 000 ; TCE 500 ; Neutrino-Astronomie ; Sonstige Instrumente {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
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  • 11
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    Aktive Regionen der Sonnenoberfläche und ihre zeitliche Variation in zweidimensionaler Spektro-Polarimetrie (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Die Arbeit beschreibt die Analyse von Beobachtungen zweier Sonnenflecken in zweidimensionaler Spektro-Polarimetrie. Die Daten wurden mit dem Fabry-Pérot-Interferometer der Universität Göttingen am Vakuum-Turm-Teleskop auf Teneriffa erfasst. Von der aktiven Region NOAA 9516 wurde der volle Stokes-Vektor des polarisierten Lichts in der Absorptionslinie bei 630,249 nm in Einzelaufnahmen beobachtet, und von der aktiven Region NOAA 9036 wurde bei 617,3 nm Wellenlänge eine 90-minütige Zeitserie des zirkular polarisierten Lichts aufgezeichnet. Aus den reduzierten Daten werden Ergebniswerte für Intensität, Geschwindigkeit in Beobachtungsrichtung, magnetische Feldstärke sowie verschiedene weitere Plasmaparameter abgeleitet. Mehrere Ansätze zur Inversion solarer Modellatmosphären werden angewendet und verglichen. Die teilweise erheblichen Fehlereinflüsse werden ausführlich diskutiert. Das Frequenzverhalten der Ergebnisse und Abhängigkeiten nach Ort und Zeit werden mit Hilfe der Fourier- und Wavelet-Transformation weiter analysiert.
    Description: thesis
    Keywords: 523 ; TGC 520 ; TGC 100 ; Sonnenflecken {Astronomie} ; Sonnenbeobachtung {Astronomie}
    Language: German
    Type: monograph , publishedVersion
    Format: 117 S.
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  • 12
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    The spectral energy distribution of polars (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: Magnetic cataclysmic variables, also called AM Her stars or 'polars', are close binaries with mass transfer (accretion), consisting of a late-type main-sequence star (commonly called secondary)and a more massive white dwarf with a strong magnetic field. The late-type star is losing mass to the white dwarf. The overflowing matter firstly follows a ballistic trajectory and is then captured by the magnetic field of the white dwarf and guided along the field lines onto the white dwarf. The released gravitational energy is radiated away in all wavelength ranges from infra-red to X-ray. The observed light of an AM Her system is composed of the contributions from the stellar components and the contributions of the accretion column and the accretion region on the white dwarf. The last two components are not only depending on the actual mass transfer rate but also from the spatial orientation of the magnetic field. Since the white dwarf is locked in synchronous rotation, this leads to emission that varies with orbital phase. The decomposition of the observed light from an AM Her system makes it possible to analyse the different components within this system...
    Description: thesis
    Keywords: 523 ; THK 000 ; Spektren und Spektroskopie von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 140 S.
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  • 13
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    The transverse proximity effect in quasar spectra (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: The intergalactic medium is kept highly photoionised by the intergalactic UV background radiation field generated by the overall population of quasars and galaxies. In the vicinity of sources of UV photons, such as luminous high-redshift quasars, the UV radiation field is enhanced due to the local source contribution. The higher degree of ionisation is visible as a reduced line density or generally as a decreased level of absorption in the Lyman alpha forest of neutral hydrogen. This so-called proximity effect has been detected with high statistical significance towards luminous quasars. If quasars radiate rather isotropically, background quasar sightlines located near foreground quasars should show a region of decreased Lyman alpha absorption close to the foreground quasar. Despite considerable effort, such a transverse proximity effect has only been detected in a few cases...
    Description: thesis
    Keywords: 523 ; 550 ; TIE 400 ; TIE 900 ; Sonstige Sternensysteme {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 144 S.
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  • 14
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    X-ray and optical properties of X-ray luminous active galactic nuclei (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Giacconi et al. (1962) discovered a diffuse cosmic X-ray background with rocket experiments when they searched for lunar X-ray emission. Later satellite missions found a spectral peak in the cosmic X-ray background at ~30 keV. Imaging X-ray satellites such as ROSAT (1990-1999) were able to resolve up to 80% of the background below 2 keV into single point sources, mainly active galaxies. The cosmic X-ray background is the integration of all accreting super-massive (several million solar masses) black holes in the centre of active galaxies over cosmic time. Synthesis models need further populations of X-ray absorbed active galaxy nuclei (AGN) in order to explain the cosmic X-ray background peak at ~30 keV. Current X-ray missions such as XMM-Newton and Chandra offer the possibility of studying these additional populations...
    Description: thesis
    Keywords: 523 ; 550 ; TBK 000 ; TIE 900 ; Hochenergieastronomie ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 226 S.
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  • 15
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    Data analysis of continuous gravitational waves (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: This thesis describes two main projects; the first one is the optimization of a hierarchical search strategy to search for unknown pulsars. This project is divided into two parts; the first part (and the main part) is the semi-coherent hierarchical optimization strategy. The second part is a coherent hierarchical optimization strategy which can be used in a project like Einstein@Home. In both strategies we have found that the 3-stages search is the optimum strategy to search for unknown pulsars. For the second project we have developed a computer software for a coherent Multi-IFO (Interferometer Observatory) search. To validate our software, we have worked on simulated data as well as hardware injected signals of pulsars in the fourth LIGO science run (S4). While with the current sensitivity of our detectors we do not expect to detect any true Gravitational Wave signals in our data, we can still set upper limits on the strength of the gravitational waves signals...
    Description: thesis
    Keywords: 523 ; 550 ; TFA 000 ; Relativistische Astrophysik, Gravitation
    Language: English
    Type: monograph , publishedVersion
    Format: 135 S.
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  • 16
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    Cold climate landforms on Mars (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: This work covers the dominant aspects of landforms and processes related to the cold-climate (periglacial) and hyperarid environment of Mars and relates the knowledge obtained from terrestrial research to possible Martian analogue landforms. Among the plethora of landforms related to cold-climate environments and subsurface permafrost on Mars, those features have been investigated in detail that are related to the creep of ice and debris at the Martian dichotomy escarpment and the southern-hemispheric impact basins, especially Hellas Planitia, and which have been described controversially as either glacial or periglacial in nature. Structures related to seasonal freeze-thaw cycles on Mars which are generally known as thermal contraction polygons form a second major focus of this work. Research presented on this topic focuses on the northern hemispheric Utopia Planitia area and the south-polar cap of Mars. This work was carried out on the basis of observational and geomorphometrical analyses by utilizing imaging-sensor and topographic data in order to address questions regarding the history, development, and current state of cold-climate landforms on Mars. This work provides new insights with respect to age, composition, source of debris and ice, and the deformational and degradational history of lobate debris aprons and similar landforms. It is shown that processes which led to creep of debris and ice at the northern hemispheric dichotomy boundary are transitional in nature and are not easily categorized using standard definitions commonly used in terrestrial research...
    Description: thesis
    Keywords: 523 ; 550 ; V 600 ; VAR 800 ; TGG 545 ; Grenzgebiete. Beziehungen. Wirkungen. Einflüsse {Geologische Wissenschaften} ; Periglazialerscheinungen ; Marsoberfläche {Astronomie}
    Language: German
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  • 17
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    Thermische Evolution und Habitabilität erdähnlicher Exoplaneten (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: In der vorliegenden Arbeit werden Methoden der Erdsystemanalyse auf die Untersuchung der Habitabilität terrestrischer Exoplaneten angewandt. Mit Hilfe eines parametrisierten Konvektionsmodells für die Erde wird die thermische Evolution von terrestrischen Planeten berechnet. Bei zunehmender Leuchtkraft des Zentralsterns wird über den globalen Karbonat-Silikat-Kreislauf das planetare Klima stabilisiert. Für eine photosynthetisch-aktive Biosphäre, die in einem bestimmten Temperaturbereich bei hinreichender CO2-Konzentration existieren kann, wird eine Überlebenspanne abgeschätzt. Der Abstandsbereich um einen Stern, in dem eine solche Biosphäre produktiv ist, wird als photosynthetisch-aktive habitable Zone (pHZ) definiert und berechnet. Der Zeitpunkt, zu dem die pHZ in einem extrasolaren Planetensystem endgültig verschwindet, ist die maximale Lebenspanne der Biosphäre. Für Supererden, massereiche terrestrische Planeten, ist sie umso länger, je massereicher der Planet ist und umso kürzer, je mehr er mit Kontinenten bedeckt ist. Für Supererden, die keine ausgeprägten Wasser- oder Landwelten sind, skaliert die maximale Lebenspanne mit der Planetenmasse mit einem Exponenten von 0,14. Um K- und M-Sterne ist die Überlebensspanne einer Biosphäre auf einem Planeten immer durch die maximale Lebensspanne bestimmt und nicht durch das Ende der Hauptreihenentwicklung des Zentralsterns limitiert...
    Description: thesis
    Keywords: 523 ; THX 500 ; THX 500 ; Exoplaneten {Astronomie: Extrasolare Planetensysteme}
    Language: German
    Type: monograph , publishedVersion
    Format: 88 S.
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  • 18
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    Surface properties of asteroids from mid-infrared observations and thermophysical modeling (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: The subject of this work is the physical characterization of asteroids, with an emphasis on the thermal inertia of near-Earth asteroids (NEAs). Thermal inertia governs the Yarkovsky effect, a non-gravitational force which significantly alters the orbits of asteroids up to ~20 km in diameter. Yarkovsky-induced drift is important in the assessment of the impact hazard which NEAs pose to Earth. Yet, very little has previously been known about the thermal inertia of small asteroids including NEAs.Observational and theoretical work is reported. The thermal emission of asteroids has been observed in the mid-infrared (5-35 æm) wavelength range using the Spitzer Space Telescope and the 3.0 m NASA Infrared Telescope Facility, IRTF; techniques have been established to perform IRTF observations remotely from Berlin. A detailed thermophysical model (TPM) has been developed and extensively tested; this is the first detailed TPM shown to be applicable to NEA data.
    Description: thesis
    Keywords: 523 ; 550 ; TGG 900 ; Planetoide {Astronomie}
    Language: English
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  • 19
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    The influence of temperature fluctuations on dust formation in dust driven winds of asymptotic giant branch stars (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; 550 ; TH0 000 ; THP 000 ; THT 600 ; Asteroseismologie, Oszillation {Sterne} ; Thermodynamische Vorgänge in Sternen {Astronomie} ; Riesensterne {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 135 S.
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  • 20
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    Measurement of the energy spectrum of the BL Lac object PG1553+113 with the MAGIC telescope in 2005 and 2006 (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: In dieser Doktorarbeit wurden im Rahmen des MAGIC Experimentes neue Datenanalysemethoden implementiert, die sich insbesondere fuer die Analyse von Ereignissen niedriger Gammastrahlungsenergie eignen. Die Methoden konnten erfolgreich in Monte Carlo Studien getestet und auf Beobachtungsdaten des Krebsnebels und der extragalaktischen Gammastrahlungsquelle PG1553+113 angewandt werden. Diese Methoden reichen von ''image cleaning'' Techniken und der Nutzung neuer Bildparameter bis zu fortgeschrittenen g/h-Separations- und Energieabschaetzungsverfahren. Zum ersten Mal wurden die Vorteile von Klassifikations- und Regressionsbaeumen in der Gamma-Astrophysik ausgenutzt, um existierende klassische Methoden zu verbessern. Die Analyse - getestet an Monte Carlo Daten - bewies ihre Zuverlaessigkeit bei der Untersuchung der Gammastrahlungsemission des Krebsnebels, wobei ein hochsignifikanter Exzess im Energiebereich unterhalb 100 GeV in nur 1.7 h nachgewiesen werden konnte. Die Analyse von Daten des BL Lac Objekts PG1553+113 ergab signifikante Exzesse fuer Beobachtungen in den Jahren 2005 und 2006. Das kombinierte alpha-Histogramm zeigt ein Signal mit einer Signifikanz, die 8 sigma ueberschreitet...
    Description: thesis
    Keywords: 523 ; TBK 000 ; THT 200 ; Hochenergieastronomie ; Sterne einzelner Spektralklassen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 195 S.
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  • 21
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    Electron acceleration at localized wave structures in the solar corona (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Our dynamic Sun manifests its activity by different phenomena: from the 11-year cyclic sunspot pattern to the unpredictable and violent explosions in the case of solar flares. During flares, a huge amount of the stored magnetic energy is suddenly released and a substantial part of this energy is carried by the energetic electrons, considered to be the source of the nonthermal radio and X-ray radiation. One of the most important and still open question in solar physics is how the electrons are accelerated up to high energies within (the observed in the radio emission) short time scales. Because the acceleration site is extremely small in spatial extent as well (compared to the solar radius), the electron acceleration is regarded as a local process. The search for localized wave structures in the solar corona that are able to accelerate electrons together with the theoretical and numerical description of the conditions and requirements for this process, is the aim of the dissertation...
    Description: thesis
    Keywords: 523 ; TGC 765 ; Korona {Astronomie: Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 109 S.
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  • 22
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    Circumplanetary dust dynamics (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Our Solar system contains a large amount of dust, containing valuable information about our close cosmic environment. If created in a planet's system, the particles stay predominantly in its vicinity and can form extended dust envelopes, tori or rings around them. A fascinating example of these complexes are Saturnian rings containing a wide range of particles sizes from house-size objects in the main rings up to micron-sized grains constituting the E ring. Other example are ring systems in general, containing a large fraction of dust or also the putative dust-tori surrounding the planet Mars. The dynamical life'' of such circumplanetary dust populations is the main subject of our study...
    Description: thesis
    Keywords: 523 ; TGL 800 ; Interplanetarer Staub {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 115, 10 Bl.
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  • 23
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    Formation and stability of the solar tachocline in MHD simulations (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; TGC 800 ; TGC 800 ; Magnetfelder {Astronomie: Sonne}
    Language: English
    Type: monograph , publishedVersion
    Format: 88 Bl.
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  • 24
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    Stellar iron core collapse in {3+1} general relativity and the gravitational wave signature of core-collapse supernovae (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae.
    Description: thesis
    Keywords: 523 ; THU 162 ; TFA 000 ; Supernovae {Astronomie} ; Relativistische Astrophysik, Gravitation
    Language: English
    Type: monograph , publishedVersion
    Format: 291 S
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  • 25
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    Quantitative models of AGB populations with subsolar metallicities and their mass loss (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: thesis
    Keywords: 523 ; THP 000 ; Thermodynamische Vorgänge in Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 76 S.
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  • 26
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    Study of the gas and dust activity of recent comets (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: Comets belong to the most pristine objects in the Solar System. The study of comets therefore allows one to put constraints to the physical and chemical conditions in the pre-planetary disc. In this work, a one-dimensional simplified multi-fluid model for the analysis of the chemistry in cometary comae was constructed. This model was used for the study of the formation of the C3 and C2 radicals. For this purpose, radial profiles of the optical emissions of C3 and C2 in comets C/2001 Q4 NEAT, C/2002 T7 LINEAR, and 9P/Tempel 1 at heliocentric distances between 1.0 AU and 1.5 AU were analysed. These profiles were obtained by means of long-slit spectroscopy. A reaction network for the formation of C3 and C2 at larger heliocentric distances (Helbert 2002) was updated and extended. Molecules and radicals were identified for which photodissociation reaction rates have to be further constrained before the formation of C3 and C2 can be understood. As comets of special interest, the comets 67P/Churyumov-Gerasimenko and 9P/Tempel 1 were studied in more detail. Both comets are targets of space missions...
    Description: thesis
    Keywords: 523 ; TGL 200 ; Kometen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 227 S.
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  • 27
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    The role of binary stars in searches for extrasolar planets by microlensing and astrometry (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: 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...
    Description: thesis
    Keywords: 523 ; THX 100 ; TDC 000 ; Detektionsmethoden {Astronomie: Extrasolare Planetensysteme} ; Astrometrie
    Language: English
    Type: monograph , publishedVersion
    Format: 153 S.
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  • 28
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    On the relevance of adhesion (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Seit ihrer Entdeckung im Jahre 1610 durch Galileo Galilei faszinieren die Ringe des Saturn sowohl Laien als auch Experten. Planetare Ringe finden sich in der Äquatorialebene aller vier Riesenplaneten unseres Sonnensystems und sind eines der eindruckvollsten Beispiele granularer Gase. Darunter gehören die Saturnringe zu den Bekanntesten. Sie bergen eine Vielzahl von Strukturen und erstrecken sich über mehr als 240 000 Kilometer, wobei sie weit weniger als 100 Meter dick sind. Unzählige kleinerer Körper bewegen sich auf leicht exzentrischen Kepler-ähnlichen Bahnen um den Zentralplaneten und bestehen dabei vorwiegend aus Eis. Die seit Juli 2004 im Orbit um den Saturn befindliche Raumsonde Cassini liefert atemberaubende Bilder und Daten, die nicht nur neue Erkenntnisse liefern, sondern auch alte Fragestellungen neu aufleben lassen. Dazu gehört z.B. die Frage nach dem Ursprung und den Entwicklungsstufen planetarer Ringe. Kürzlich, im äusseren A-Ring entdeckte Kleinmonde, deren Existenz schon viel früher postuliert wurde, weisen auf eventuell stattfindende Wachstumsprozesse hin. Da sich planetare Ringe jedoch hauptsächlich innerhalb der sogenannten Roche-Zone des jeweiligen Planeten befinden, ist ein effektives, allein auf gravitativen Wechselwirkungen beruhendes Größenwachstum nicht zu erwarten. Der Einfluß von Teilchenadhäsion auf diese Prozesse ist bis dato fraglich.
    Description: thesis
    Keywords: 523 ; TGE 590 ; TGG 650 ; Planetenringe {Astronomie} ; Saturn {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 106 S.
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  • 29
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    Properties of turbulent star-forming clusters (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Sterne entstehen im Inneren von turbulenten Molekülwolken, die unter dem Einfluss ihrer eigenen Gravitation fragmentieren und kollabieren. So entsteht ein Sternhaufen aus hundert oder mehr Objekten. Der Sternentstehungsprozess wird durch das Wechselspiel von Überschallturbulenz und Gravitation reguliert. In dieser Arbeit werden verschiedene Eigenschaften solcher Sternhaufen, die mit Hilfe von numerischen Simulationen modelliert wurden, untersucht und mit Beobachtungsdaten verglichen. Dabei handelt es sich sowohl um Eigenschaften einzelner Protosterne, als auch um statistische Parameter des Sternhaufens als Ganzes...
    Description: thesis
    Keywords: 523 ; TIC 000 ; TEG 000 ; Sternhaufen {Astronomie} ; Kosmogonie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 138 S.
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  • 30
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    Indirect imaging of AM Herculis-stars (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: AM Herculis stars (or 'polars') are close binaries consisting of a white dwarf with a strong magnetic field and a main sequence star (the 'secondary') which is losing mass to the white dwarf. The magnetic field channels the matter to the magnetic poles, where the released potential energy is radiated away - mainly in X-rays and the UV. The spatial structure of these objects cannot be observed directly, because their apparent size is too small. Indirect imaging methods are capable of restoring information which is only contained in observational data as projections onto a sub-space. These tomographic methods are known from medicine, but can also be applied to astronomical data, when a number of measurements can be regarded as views of the same object under different aspect angles. In this work tomographic methods are applied to time-resolved spectroscopic data of polars. Spectral lines seen in the radiation emitted by the constituents of these systems are notably Doppler-shifted. The Doppler-shift is depending on the viewing angle of the system ('inclination') and is varying with orbital phase. Time-series of one-dimensional data (spectra) can be used to create a two-dimensional map of the intensity distribution in velocity-space (Doppler-tomography), or a map of the line-flux on the assumed surface of the mass-losing star (Roche-tomography) from the line profile changes ...
    Description: thesis
    Keywords: 523 ; THT 900 ; THU 155 ; Doppelsterne {Astronomie} ; Eruptionsveränderliche {Astronomie: Sterne}
    Language: English
    Type: monograph , publishedVersion
    Format: 124 S.
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  • 31
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    Cosmological solutions of the Einstein-Vlasov-scalar field system (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: The aim of this thesis is to obtain as much information as possible, about global solutions of the Cauchy problem for the Einstein-Vlasov-scalar field system with spherical, plane and hyberbolic symmetries written in areal coordinates. The sources of this system are generated by both a distribution function and a linear scalar field subject to the Vlasov and wave equations respectively. This system describes the evolution of self-gravitating collisionless matter and scalar waves within the context of general relativity. We consider the cosmological case. That is spacetimes possess a compact Cauchy hypersurface and then, data are given on a compact 3-manifold. We extend the local-in-time results obtained by G. Rein for the Einstein-Vlasov system with collisionless matter alone. This extension concerns pointwise estimates for hyperbolic equations by the method of characteristics. This means that the system is transformed to a system of ordinary differential equations which are integrated along characteristics ...
    Description: thesis
    Keywords: 523 ; TFA 000 ; Relativistische Astrophysik, Gravitation
    Language: English
    Type: monograph , publishedVersion
    Format: 85 S.
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  • 32
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    Cosmology through gravitational lenses (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: In dieser Dissertation nutze ich den Gravitationslinseneffekt, um eine Reihe von kosmologischen Fragen zu untersuchen. Der Laufzeitunterschied des Gravitationslinsensystems HE1104-1805 wurde mit unterschiedlichen Methoden bestimmt. Zwischen den beiden Komponenten erhalte ich einen Unterschied von Delta_t(A-B) = -310 +-20 Tagen (2 sigma Konfidenzintervall). Außerdem nutze ich eine dreijährige Beobachtungskampagne, um den Doppelquasar Q0957+561 zu untersuchen. Die beobachteten Fluktuationen in den Differenzlichtkurven lassen sich durch Rauschen erklären, ein Mikrogravitationslinseneffekt wird zur Erklärung nicht benötigt...
    Description: thesis
    Keywords: 523 ; TEG 400 ; TFA 000 ; Endstadien von Sternen {Astronomie: Kosmogonie} ; Relativistische Astrophysik, Gravitation
    Language: English
    Type: monograph , publishedVersion
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    Numerical simulations of neutron star - black hole mergers (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Collisions of black holes and neutron stars, named mixed binaries in the following, are interesting because of at least two reasons. Firstly, it is expected that they emit a large amount of energy as gravitational waves, which could be measured by new detectors. The form of those waves is expected to carry information about the internal structure of such systems. Secondly, collisions of such objects are the prime suspects of short gamma ray bursts. The exact mechanism for the energy emission is unknown so far...
    Description: thesis
    Keywords: 523 ; TEG 400 ; Endstadien von Sternen {Astronomie: Kosmogonie}
    Language: English
    Type: monograph , publishedVersion
    Format: 205 S.
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  • 34
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    Developing a ground-based search system for transits of extrasolar planets (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: The search for extrasolar planets is a relatively new field in astronomical and astrophysical sciences that was boosted by the first discovery of the exoplanet 51 Peg b in 1995 by radial velocity measurements. The short orbital period of 4.2 days determined for this giant exoplanet encouraged the accelerated development of another search method due to the high probability that such a Hot Jupiter planet would cross its host star in the line of sight yielding a photometrically detectable signal during this crossing. This transit method (also known as the occultation or eclipse method) measures such a darkening signal as an evidence for an orbiting planet allowing the determination of the radius of the planet. Combined with the information obtained with radial velocity measurements the mass and the density of the planet can be calculated. This unique opportunity to study detailed physical properties of exoplanets is advantageous compared to planets proven only by other search methods. In this thesis the establishing of the new ground-based transit survey Berlin Exoplanet Search Telescope (BEST) is described. This system consists of a 20cm Schmidt telescope and a CCD camera covering a field of view (FOV) of 3.1ʿ x 3.1ʿ. The set-up and the successful implementation of the BEST system are described in this work. Furthermore the developed strategies for the photometric observations, the calibration and analysis of the data, follow-up observations and their optimization are commented. During the 2-year observational campaign (2001-2003) from the Thüringer Landessternwarte (TLS) Tautenburg, Germany, three target fields were observed for 90 nights ...
    Description: thesis
    Keywords: 523 ; THX 100 ; Detektionsmethoden {Astronomie: Extrasolare Planetensysteme}
    Language: English
    Type: monograph , publishedVersion
    Format: 269 S.
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  • 35
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    Probing quasar sight lines in three dimensions (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: Strong damped Lyman alpha absorption (DLA) lines seen spectra of distant quasar are believed to arise when the sight line to the quasar goes trough the disc of a galaxy or a proto galaxy. Most of the neutral matter in the universe is contained in these clouds of neutral hydrogen that cause the absorption lines. Hence these DLAs are reservoirs for the formation of stars and galaxies throughout the universe. Despite intensive efforts over more than two decades only few galaxies responsible for the DLAs have been found. The problem is that the galaxies that harbour the neutral clouds are not necessarily bright, and selecting galaxies based on absorption lines could well select different types of galaxies than found in large surveys. If we are to understand how galaxies form out of neutral gas clouds it is essential to locate the galaxies in which DLAs reside ...
    Description: thesis
    Keywords: 523 ; TIE 900 ; TIE 400 ; Sonstige Sternensysteme {Astronomie} ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 187 S.
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  • 36
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    Present and early star formation (2010)
    Univ. Potsdam
    Details
    Publication Date: 2021-03-29
    Description: We investigate the rotational and thermal properties of star-forming molecular clouds using hydrodynamic simulations. Stars form from molecular cloud cores by gravoturbulent fragmentation. Understanding the angular momentum and the thermal evolution of cloud cores thus plays a fundamental role in completing the theoretical picture of star formation. This is true not only for current star formation as observed in regions like the Orion nebula or the ?-Ophiuchi molecular cloud but also for the formation of stars of the first or second generation in the universe...
    Description: thesis
    Keywords: 523 ; TEG 000 ; Kosmogonie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 149 S.
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  • 37
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    Optical variability of counterparts of ROSAT X-ray sources near the north ecliptic pole (2010)
    Univ. Berlin
    Details
    Publication Date: 2021-03-29
    Description: Optical counterparts of X-ray selected sources to a large part consist of active galactic nuclei (AGN). A large proportion of these counterparts turns out to be optically variable, and because the timescales and manner of this variability can give important clues regarding the physical nature and structure of the counterparts, searching for variable AGN is a worthwhile undertaking. In order to perform such an optical variability survey, a subset of 167 X-ray sources in an area around the NEP was selected in this work from the X-ray catalogues derived from the ROSAT all-sky survey (RASS). Contemporaneous optical observations were available from a collaboration with the Karl-Schwarzschildt observatory (KSO) Tautenburg. A total of 89 plates were analyzed, covering an area of 35 degrees square around the NEP and spanning a timebase of 30 month ...
    Description: thesis
    Keywords: 523 ; TBK 000 ; TC 200 ; Hochenergieastronomie ; Astronomische Beobachtungen vom Weltraum aus
    Language: English
    Type: monograph , publishedVersion
    Format: 283 S.
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