ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    Properties of quasistellar objects and their progenitors in the radio and mm wavelength regimes in the context of ULIRG-to-QSO evolution (2010)
    Univ. Köln
    Details
    Publication Date: 2020-10-07
    Description: The thesis at hand presents the results of a study of galaxies with active galactic nuclei (AGN) carried out in the radio and mm wavelength regimes at low and high angular resolutions. The studied objects cover a broad range of mechanisms responsible for powering the engines of the respective galaxies: ULIRGs (UltraLuminous Infrared Galaxies), a product of mergers between galaxies that are supposedly powered by starbursts, AGN or a mixture of the two, and QSOs (quasi-stellar objects) which are powered by AGN. Since ULIRGs and QSOs show similar properties (especially the infrared luminosities), it was proposed that they form the early and late phase of an evolutionary sequence where supposedly ULIRGs are the dust enshrouded progenitors of QSOs. As a prototypical ULIRG, Arp 220 represents an early-to-intermediate phase object in the scheme of the ULIRG-to-QSO evolution. For this object observations at multiple mm wavelengths and angular resolutions with the IRAM Plateau de Bure Interferometer (PdBI) are presented and analyzed. Arp 220 as a whole is studied in CO emission of the more extended structure. Furthermore, Arp 220-East is analyzed in more detail in the CO gas. Indications for emission ~10" towards the south, as well as to the north and to the west of the two nuclei, were found in the low resolution CO(1-0) maps ...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 523 ; TBC 000 ; TIE 900 ; Radioastronomie ; Sonstige Sternensysteme {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 152 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 2
    facet.materialart.
    Unknown
    Multi-telescope studies of neutron stars (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: 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...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 523 ; THU 400 ; THK 000 ; TBC 000 ; Pulsare, Neutronensterne {Astronomie} ; Spektren und Spektroskopie von Sternen {Astronomie} ; Radioastronomie
    Language: English
    Type: monograph , publishedVersion
    Format: 152 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 3
    facet.materialart.
    Unknown
    The fate of singularities in quantum cosmology and the application of generalized effective equations to constrained quantum systems (2010)
    Univ. Köln
    Details
    Publication Date: 2020-10-07
    Description: The first part of the thesis is concerned with the fate of singularities in quantum cosmology. The second part addresses the derivation of predictions from quantum cosmology. In the first part, two classes of cosmological models were studied. In the first class of models, the universe evolves to or emerges from a big-rip singularity. Here, energy density, pressure and scale factor diverge after a finite amount of time. This type of singularity arises rather generically in cosmological models with phantom dark energy. For each of these phantom-field models, the corresponding scenario with ordinary scalar field was studied. The scalar field induced a big-bang singularity. The second class of models studied was dominated by a big-brake singularity. At the big brake, the universe evolution comes to a halt due to an infinite deceleration. The motivation behind this choice of models was the occurrence of a singularity at large scale factor. The major question pursued was whether these types of singularity were resolved on the quantum level. If such singularities were resolved in quantum cosmology, this would imply that quantum gravitational effects can occur in the macroscopic universe. After devising classical models that contain the respective singularity, I subjected these models to quantization which was carried out in the geometrodynamical approach. The governing equation is then the WheelerDeWitt equation ...
    Description: Zsfassung in dt. und engl. Sprache
    Description: thesis
    Keywords: 523 ; TEC 800 ; Quantenkosmologie {Astronomie: Kosmologie}
    Language: English
    Type: monograph , publishedVersion
    Format: 228 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 4
    facet.materialart.
    Unknown
    Star-disc encounters in young star clusters (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: 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 can lead to a total disc destruction ...
    Description: thesis
    Keywords: 523 ; THX 000 ; TIC 000 ; Extrasolare Planetensysteme {Astronomie: Sterne} ; Sternhaufen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 137 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 5
    facet.materialart.
    Unknown
    Periodic variability in active galactic nuclei (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: In this doctoral thesis, multi-frequency very long baseline interferometry observations together with multi-frequency total flux-density variability data of compact relativistic jets in active galactic nuclei are presented and analyzed. The main goal of the thesis is to investigate the physical mechanisms in relativistic jets responsible for such phenomena as the co-existence of moving and stationary jet components, jet wiggling and precession. We also aim to study the connection between the structural changes in the relativistic jets and flares in the total flux-density light curves and to find observational evidences for the appearance of a primary perturbation in the base of the jet and its further propagation. In this thesis we also investigate which physical mechanisms are responsible for periodical total flux-density variability and to search for periodicities as a sign of jet precession. In order to study the jet physics we used the multi-frequency very long baseline interferometry technique which gives the highest possible in astronomy resolution. We also compared jet structural changes with single-dish multi-frequency observations spanning more than 30 years together with optical and gamma-ray data. In particular, analysis of the long-term kinematics of two active galactic nuclei S5 1803+784 and 0605-085 shows evidence for jet precession ...
    Description: thesis
    Keywords: 523 ; TBC 000 ; TIE 500 ; Radioastronomie ; Aufbau und Struktur von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 201 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 6
    facet.materialart.
    Unknown
    Star formation conditions in nearby galaxies (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The understanding of gravitational stability of galactic disks against star formation, the interplay of atomic and molecular components of the interstellar medium in a galaxy and its physical conditions, namely temperature and density, are important to gain a deeper insight into star formation. Nearby galaxies like the spiral galaxy M51 or the southern starburst galaxies NGC4945 and Circinus offer excellent opportunities to investigate these topics over a complete galactic disk or parts of the galaxy. A suitable tracer to study the molecular part of the gaseous component of galaxies is the CO molecule. It is the second most abundant molecule after H2 in the interstellar medium, its lower lying transition are excited at typical conditions of molecular clouds and the rotational transitions lie in the radio window. Thus, CO emission can penetrate throughout galactic disks and is observable from the ground. Apart from complementary data from the literature, we use observations of 12CO 21, 12CO 4--3, and 13CO 2--1 in this thesis. Additionally, the [CI] 3P1-3P0 fine structure line was observed to study the physical conditions in the central regions of galaxies. In the first part of this thesis, the nearby spiral galaxy M51 is used as a sample source to investigate the onset of star formation. CO, HI, radio-continuum, dust, and stellar maps of M51 are combined to study star formation rate, the H2/HI transition, the gas-to-dust ratios, the stability of the disk against gravitational collapse, and properties of the giant molecular clouds. Parts of the results have been published in Astronomy and Astrophysics (461,143) in 2007 and are submitted to Astronomy and Astrophysics, 2008 for publication. We use the first complete 12CO 2--1 map of M51 including the companion galaxy NGC5195 observed with HERA at the IRAM-30m telescope to trace the molecular gas. Complementary HI VLA data is used to study the atomic gas distribution and the combined total gas surface density ...
    Description: thesis
    Keywords: 523 ; TEG 000 ; Kosmogonie {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 180 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 7
    facet.materialart.
    Unknown
    LINC-NIRVANA piston control and near-infrared polarization images of the Orion proplyds (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This thesis is focussed on the development of optimized techniques to overcome limitations of astrophysical observations. The goal is an optimal signal estimation in noisy measurements by the consideration of underlying physical processes. This principle was applied to two different fields in astrophysics: intrumental design and analysis of polarimetric observations. In the observational part of this thesis near-infrared images of young stellar objects in the Orion constellation are studied. Limitations in resolution and sensitivity of current astronomical instruments prohibit the detailed analysis of interesting proto-stellar sources to improve theories of star formation. Radiation from the astronomical targets is not only characterized by its spectral energy, but also by polarization properties. The modeling of typical configurations of star-disk systems and the simulation of their polarization patterns helped to understand and interprete features, that were found in observations. For the case of a proto-stellar systems with both a disk and an envelope analysis techniques were developed, which are based on polarimetric effects of the scattering of light by dust. These techniques substantially improve the sensitivity and resolution and are reliable under different observing conditions. Although the obtained data did not allow investigations of substructures of the circumstellar material, the techniques are suitable to obtain constraints on star formation processes ...
    Description: thesis
    Keywords: 523 ; THK 000 ; Spektren und Spektroskopie von Sternen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 168 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 8
    facet.materialart.
    Unknown
    Studying martian dust devils by applying pattern recognition algorithms to multi-mission camera images (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: A pattern recognition and classification software was developed to detect dust devils automatically in surface images from Mars. The amount of images taken by spacecraft orbiting Mars is increasing continuously and the expenditure of time is too high to search every image for spatially and temporally highly variable features like dust devils. The pattern recognition method was therefore used to conduct a completely new kind of search for dust devils. Images from the three different Mars missions Viking, Mars Global Surveyor and Mars Express can be processed and for the first time automatically scanned for the desired objects. Viking images including dust devils were used as the database to filter unique dust devil features and the derived parameters built the feature vector. Various Classification methods have been tested resulting in a two-layer perceptron (neural network) as the best classifier. Necessary adjustments and increments complete the software so that it can be applied to Mars Global Surveyor Mars Orbiter Camera (MOC), Mars Express High Resolution Stereo Camera (HRSC) and probably coming images from future missions. It was shown that the standard dust devil is filtered and correctly classified. The two main features, the bright spot representing the dust column and the shadow, must be filterable from the background. Crater rims and hills are the most false-positive objects...
    Description: thesis
    Keywords: 523 ; TGG 545 ; TGG 515 ; TCM 000 ; TCE 380 ; Marsoberfläche {Astronomie} ; Marsbeobachtung, Raumflüge zum Mars {Astronomie} ; Mathematische und EDV-Verfahren {Astronomie} ; CCD, Photodetektoren {Astronomische Instrumente}
    Language: English
    Type: monograph , publishedVersion
    Format: 158 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 9
    facet.materialart.
    Unknown
    Dissecting the host galaxies of active galactic nuclei at high angular resolution (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: The work presented here is concerned with issues related to the interplay of galaxy structure and the accretion phenomenon onto supermassive black holes (SMBH), i.e. active galactic nuclei (AGN). There is statistical evidence for a coevolution of SMBHs and the galaxy bulges they reside in. The detailed knowledge of the involved physical processes, however, is still far from being satisfactory. In order to test and improve theoretical models of how this coevolution is arising, high angular resolution observations of the host galaxies of AGN are necessary. Imaging and spectroscopy of the innermost region of galaxies have the power to reveal information on the structure, the chemical composition, and the dynamics of stars and gas in the presence of an SMBH, and allow us to separate energetic signatures related either to star formation or to the accretion onto the SMBH. Considering such observations over cosmological distances (redshifts) -- i.e. looking into the past because of the finite light-travel time -- we are also able to assess evolutionary effects on the beforementioned properties ...
    Description: thesis
    Keywords: 523 ; TIE 400 ; Spektren und Leuchtkraft von Sternsystemen {Astronomie}
    Language: English
    Type: monograph , publishedVersion
    Format: 174 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 10
    facet.materialart.
    Unknown
    Cophasing LINC-NIRVANA and molecular gas in low-luminosity QSO host and cluster galaxies (2010)
    Univ. Köln
    Details
    Publication Date: 2021-03-29
    Description: This thesis consists of two parts. The first part reports on the development of a fringe tracking system for LINC-NIRVANA, the near-infrared homothetic imaging camera for the Large Binocular Telescope (LBT). LINC-NIRVANA allows for a coherent combination of the light entering the two primary mirrors. The fringe pattern in the focal plane is required to be stable in time to preserve the high spatial frequency information in long exposure images. Atmospheric differential piston causes the position of the fringes to change with time. A fringe tracker is a servo system that measures and corrects for atmospheric differential piston in real-time. In the first part, numerical simulations of atmospheric turbulence are used to investigate the problem of angular anisoplanatism of differential piston. The fringe tracking concept and the top-level requirements are introduced, followed by a presentation of the mechanical design of the system. This design includes a solution for a device that is capable of positioning a detector with high precision within a cryogenic environment. A fitting algorithm determines the amount of differential piston in the point-spread function of a reference target. The performance of this algorithm under different signal-to-noise conditions is investigated. First polychromatic fringes obtained with a testbed interferometer conclude the first part ...
    Description: thesis
    Keywords: 523 ; TII 500 ; Emissionsnebel {Astronomie: Interstellare Materie}
    Language: English
    Type: monograph , publishedVersion
    Format: 186 S.
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...