Jan-Uwe Ness (European Space Astronomy Centre, ESA)
The X-ray plasma diagnostics of optically thin plasma in collisional equilibrium as developed for coronal plasma can also be applied to other astrophysical environments to which the underlying assumptions apply. The technique of reconstructing the differential Emission Measure Distribution (EMD) from high-resolution X-ray spectra has been applied to X-ray grating spectra taken of the recurrent nova RS Ophiuchi, 13.8 days after its 2006 outburst. At this time, the fast-moving nova ejecta dissipated kinetic energy in the slow stellar wind of the evolved companion star, leading to collisionally ionised plasma that produced X-ray emission lines and bremsstrahlung continuum. A 3-temperature APEC plasma model yields good reproduction of the observed spectra, justifying a detailed EMD analysis. The spectra are extremely well exposed, and a comparison between the global spectral fitting approach and the line-based approach exposes the strengths and weaknesses of the two methods. The most important results are consistent with both methods, yielding relative abundances and the temperature structure. The abundance measurements deliver an important argument against RS Oph being a supernova Ia progenitor.
Talk presented at the symposium From Atoms to Stars: the Impact of Spectroscopy on Astrophysics, 26-28 July 2011, Oxford University, UK.