Excitation of stellar pulsations

Stars can self-excite oscillations if a driving mechanism operates in suitable interior or exterior regions. Several different excitation mechanisms are known, but are presently still poorly understood. For instance, this manifests itself in the overestimation of the pulsation amplitudes of stars from theoretical models. Another example is the absence of pulsations where models predict them. This project aims at understanding the excitation of stellar oscillations, thereby yielding new insights in stellar structure and physics. The aims of the project are threefold: solar-like oscillations will be searched for in stars hotter than the known representatives of this kind of variables. The pulsation amplitudes of these objects tell us about stellar surface convection in a hitherto unexplored parameter range. We intend to acquire high-precision radial velocity measurements of a suitable object to detect these oscillations, and we demonstrate that we can. Furthermore, we want to determine the interior structure of this variable from the pulsations by means of seismic analyses. Time on a large telescope has already been scheduled for this ambitious project. Another avenue of research we want to pursue is to examine so-called "hybrid" pulsators, stars that oscillate on two very different time scales simultaneously. In the beginning, we will verify whether these stars are intrinsic "hybrid" pulsators or just claimed to be so due to insufficient data. Having done so, we will follow up the most interesting cases intensively, again with the aim to determine their interior structures via seismology. In the end, we want to find out what distinguishes these stars from non-"hybrid" pulsators, invoking also high-precision spectroscopic studies. The third part of this project aims at investigating the excitation of pulsations in stars having originated from the same astrophysical environment, i.e. they should basically differ only in mass. These would be object contained in open clusters, which will be surveyed for pulsations. In this way, the physical parameter space in which pulsations take place for these stars can be tightly constrained, and it can be checked whether there is really a domain where theory predicts pulsations that cannot be observationally detected. Again, high-precision and high-resolution spectroscopy will be involved to delineate the parameter space to greatest possible detail. From this work, we hope to obtain information on the validity of present stellar model input physics, and want to contribute to their improvement.

Stars can self-excite oscillations if a driving mechanism operates in suitable interior or exterior regions. Several different excitation mechanisms are known, but are presently still poorly understood. For instance, this manifests itself in the overestimation of the pulsation amplitudes of stars from theoretical models. Another example is the absence of pulsations where models predict them. This project aims at understanding the excitation of stellar oscillations, thereby yielding new insights in stellar structure and physics. The aims of the project are threefold: solar-like oscillations will be searched for in stars hotter than the known representatives of this kind of variables. The pulsation amplitudes of these objects tell us about stellar surface convection in a hitherto unexplored parameter range. We intend to acquire high-precision radial velocity measurements of a suitable object to detect these oscillations, and we demonstrate that we can. Furthermore, we want to determine the interior structure of this variable from the pulsations by means of seismic analyses. Time on a large telescope has already been scheduled for this ambitious project. Another avenue of research we want to pursue is to examine so-called "hybrid" pulsators, stars that oscillate on two very different time scales simultaneously. In the beginning, we will verify whether these stars are intrinsic "hybrid" pulsators or just claimed to be so due to insufficient data. Having done so, we will follow up the most interesting cases intensively, again with the aim to determine their interior structures via seismology. In the end, we want to find out what distinguishes these stars from non-"hybrid" pulsators, invoking also high-precision spectroscopic studies. The third part of this project aims at investigating the excitation of pulsations in stars having originated from the same astrophysical environment, i.e. they should basically differ only in mass. These would be object contained in open clusters, which will be surveyed for pulsations. In this way, the physical parameter space in which pulsations take place for these stars can be tightly constrained, and it can be checked whether there is really a domain where theory predicts pulsations that cannot be observationally detected. Again, high-precision and high-resolution spectroscopy will be involved to delineate the parameter space to greatest possible detail. From this work, we hope to obtain information on the validity of present stellar model input physics, and want to contribute to their improvement.