Atomic Physics for Astrophysics at QUB 2006-2011

Space-based observatories (such as the Hubble Space Telescope, the Far Ultraviolet Spectroscopic Explorer and the Solar and Heliospheric Observatory, as well as the Chandra and XMM-Newton missions) have transformed the quality of the information obtained from observation of stellar objects. The electromagnetic radiation emitted by a stellar object is resolved into a spectrum by spectrographs in these observatories; and the spectrum contains many 'lines' arising from the absorption or emission of energy by atoms or ions. Our research is directed towards extracting information about the stellar object from this observed spectroscopic data. Careful analysis of wavelengths and intensities of the lines in the spectrum can yield information about the density and temperature of the object and about the relative amount of each chemical element present. To obtain useful information from the stellar spectra requires knowledge of the basic atomic processes (emission, absorption, excitation, ionization, etc) that are occurring in the stellar object. This atomic data can be determined either experimentally or through theoretical calculations. However, because of the extreme conditions found in stars, much of the required atomic data cannot, in fact, be measured experimentally. Furthermore, the amount of atomic data required is so vast that the only practical way of obtaining sufficient data is through calculations which, because atoms have very small dimensions, must be based on quantum mechanics. Our research team has a long-established experience in quantum mechanical calculations of relevant atomic properties. However, the equations of quantum mechanics, applied to atoms and ions, cannot be solved exactly, so there will always be some inaccuracy in calculations. Our links with experimental teams are therefore vital: the more limited experimental data serve as benchmarks against which to check the accuracy of the calculations. In this way, we can determine the types of calculation necessary to achieve reliable data for application to the analysis of the observational data, and we can provide a measure of the inaccuracy of the calculations. When there were only ground-based observatories, the quality of the observational data was limited by the absorbing and aberrating influence of the Earth's atmosphere. This problem does not arise with space-based observatories: there is a much greater resolution (detail) in the observational data and hence the analysis of that data now requires atomic data of much greater accuracy than was needed previously. Moreover, many of the elements which previously could not be detected because of limited resolution have now been observed. The entire observational effort, therefore, ultimately relies on the availablility of highly accurate atomic data: in many cases, existing data are of insufficient accuracy; in some cases, no data exist at all. The goal of our research is to make significant contributions to this need for new and high quality atomic data, so that the time, money and effort expended in the acquisition of the observational data can lead to maximum benefit.