PhD and Diploma
Thesis Projects
Offered for supervision by Roland Diehl, MPE
Current Projects:
High-resolution spectroscopy allows measurements of gamma-ray line shapes with ~keV precision, enabling physics interpretations in terms of thermal or Doppler broadening. Explosive nucleosynthesis ejects radioactive isotopes with velocities up to 10000 km s-1, which results in significant line shifts and line shapes which reflect kinematic and optical-depth effects. Models for expanding ejecta are developed for singel sources, and for associations of massive stars. The impact of interstellar-medium characteristics are studied, aiming at model predictions of characteristic gamma-ray line shapes for the 44Ti, 26Al, and 60Fe isotopes. The disgnostic power of line shapes is assessed in terms of inherent model uncertainties and observational limitations. Ge spectrometer gamma-ray line measurements for specific regions are interpreted in this context.
Earlier Projects:
COMPTEL data are re-analyzed with Time-of-Flight as analysis parameter. For this, a background study establishes the expected signature of signal and background events in ToF. The imaging software is re-written to include this data-space variable, and a comparison between ToF unresolved and –resolved imaging is performed in the energy band of the 26Al line with the latest ToF (VI) corrected COMPTEL database.
In a population synthesis model, nucleosynthesis yields and kinetic energy and ionizing radiation are determined. This thesis develops such a population synthesis model, assesses its proper inputs from stellar evolution models, from stellar wind models and data, from stellar atmosphere, and from nucleosynthesis models. The model is applied to analyze the structure and history of the Cygnus region. A physical treatment of a superbubble is developed, including its evolution from injection of winds and supernovae, and from encountering interstellar clouds; dynamical evolution of the superbubble, its radiation characteristics, and distribution of nucleosynthesis products in its interior are derived. This model is applied to the Cygnus Superbubble and other regions. The parameters of the Cygnus region OB associations are analyzed for overall consistency in such a model treatment.
In a population synthesis model, nucleosynthesis yields and kinetic energy and ionizing radiation are determined. This thesis analyzed the uncertainties associated with statistics and systematics from the unknowns of the stellar population and star models as well as nucleosynthesis inputs.
The COMPTEL sky survey data from >5 years of the NASA CGRO mission are analyzed for imaging the 1.809 MeV line from 26Al. For this, the instrumental background is investigated and modelled in physics details. Imaging algorithms are developed, adapted, and analyzed for their systematic uncertainties. An all-sky image of 1.809 MeV photons from 26Al is then derived, and its significances are assessed. Interpretations for Galactic sources of 26Al are discussed.
The COMPTEL
sky survey result on the 1.809 MeV line from 26Al was used as
a basis for comparisons to candidate source images and catalogues. Analysis
methods for correlating images among each other, and images with object
catalogues, were investigated. As examples, catalogues from supernova remnants
and maps of X-ray emission were compared to the gamma-ray map. It was asserted
that global correlations, noise and artifacts, and systematics in each result
makes it difficult to find a threshold for the astrophysical significance
and meaning of correlation quantities.
From the first part of the CGRO mission, the COMPTEL data from the plane of the Galaxy are analyzed for imaging the 1.809 MeV line from 26Al. For this, the 'Maximum-Entropy' Imaging algorithm is adapted to COMPTEL data space, and the instrumental background is modelled in this dataspace from physics and empirical aspects. An image of 1.809 MeV photons from 26Al is then derived for Galactic-plane regions. Interpretations for sources of 26Al are discussed in general terms, and specifically&detailed for the region of Carina.
Status: August 2003