Astrophysical atomic structure – the state-of-the-art and uncharted territories

Anand Thirumalai (Arizona State University)

February 26, 2015

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Abstract: It is a matter of great theoretical and practical concern that as of 2015, we only really know the structure of the most basic atoms, hydrogen and helium, in intense magnetic fields such as those found in white dwarfs and neutron stars (B > 10^5 T). These are the most highly magnetised objects in the observable universe. The energy levels, transition wavelengths, oscillator strengths and electric and magnetic properties of virtually the entire periodic table is almost completely unknown in such field strengths. Such atomic data is crucial for correctly interpreting the emergent spectra from magnetised compact objects, particularly since evidence is now mounting for the presence of atoms such as carbon being present in their atmospheres. In white dwarfs, there are also other species such as phosphorus, silicon and sulphur present in appreciable quantities, even in cooler and therefore older white dwarfs. This is strange due to the very short timescales for the heavier atoms to submerge in the atmospheres of white dwarfs. Thus, the older the white dwarf, the less the contaminants, and the chemistry is expected to be predominantly H or He. In neutron stars on the other the hand story is the reverse, only the younger neutron stars are expected to have H and He which are the remnants from supernova fallback material during collapse. The older neutron stars are expected to have purely heavier elements; the products of nuclear burning of lighter elements. Therefore it is now understood that the presence of low- and mid-Z elements such as carbon (and for that matter Si, P, S etc) in older varieties of both white dwarfs and neutron stars is probably due to accretion of ambient material. In this talk I shall summarize the state-of-the-art in the field of strong field atomic structure field and also describe my recent efforts in developing fast atomic structure software that computes the energy landscape of low-Z atoms in intense magnetic fields.