LINC-NIRVANA Piston Control and Near-Infrared Polarization Images of the Orion Proplyds

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. With larger telescopes, such as the Large Binocular Telescope (LBT), the analysis of principles down to the scale of planet formation will be possible. LINC-NIRVANA, the near-infrared imaging system at the LBT, will provide unprecedented resolution and sensitivity performance combined with a wide field of view. The interferometric combination of light from two telescopes imposes new challenges in the instrument design. A so-called fringe tracker is mandatory for the interference of light at the detector by compensating optical path differences with an actuated mirror. The performance suffers from structural vibrations, limited sensitivity of sensors and processing latencies. The dynamics of actuators with significant amount of moving masses are limited. These effects are studied in the instrumental part of this thesis. Giant telescopes with large mirrors and high-resolution instruments are complex, expensive projects. The telescope time, i.e. the allocated time to the observations of individual astronomical topics, is very limited and hence valuable. It is of great importance to improve the performance in terms of sensitivity and resolution of observations under difficult conditions. By modeling all performance related subsystems of the interferometric instrument critical parameters were identified. For a realistic model several precision measurements of the telescope and parts of the LINC-NIRVANA instrument were necessary. Simulations of atmospheric effects completed the model. Several approaches for the optimization of the instrument performance were proposed. The determination of atmospheric and instrumental optical path difference or differential piston is improved by the detailed analysis of the statistical variation and appropriate filtering. The application of modern control theory provides stability and optimal dynamic response of the mirror actuator. Since both parts of this thesis deal with the impact of the atmosphere on the observational result of astronomical instruments, chapter 1 gives an overview on the basic principles and techniques. Chapter 2 presents the modeling and control analysis of the fringe tracker for the LINC-NIRVANA instrument. A software simulation is introduced and first results of a laboratory experiment are denoted. Chapter 3 gives a short introduction into star formation theories and unsolved problems, followed by the detailed description of polarimetric observations of proto-stellar objects in the Orion constellation in chapter 4. Some concepts and atmospheric effects as introduced in chapter 1 are discussed. Promising findings of one source of the sample led to extensive modeling and analysis of polarimetric properties of proto-stars and the development of innovative analysis techniques, presented in chapter 5. In the last chapter these methods are applied to the observational data and the obtained configuration parameters are compared to results of previous investigations in the literature.