A&A 484, 755-771 (2008)
Optical and near-infrared recombination lines of oxygen ions from Cassiopeia A knotsD. Docenko1, 2 and R. A. Sunyaev1, 3
1 Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
2 Institute of Astronomy, University of Latvia, Raina bulvaris 19, Riga LV-1586, Latvia
3 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
Received 14 February 2008 / Accepted 21 March 2008
Context. Fast-moving knots (FMK) in the Galactic supernova remnant Cassiopeia A consist mainly of metals and allow us to study element production in supernovae and to investigate shock physics in great detail.
Aims. We discuss and suggest observations of a previously unexplored class of spectral lines, the metal recombination lines in optical and near-infrared bands, emitted by the cold ionized and cooling plasma in fast-moving knots.
Methods. By tracing ion radiative and dielectronic recombination, collisional l-redistribution and radiative cascade processes, we compute resulting oxygen, silicon and sulphur recombination line emissivities. This allows us to determine the oxygen recombination line fluxes, based on a fast-moving knot model that predicts the existence of highly-ionized ions from moderate to very low plasma temperatures.
Results. The calculations predict oxygen ion recombination line fluxes detectable with modern optical telescopes in the wavelength range from 0.5 to 3 m. Recombination line flux ratios to collisionally-excited lines will allow us to probe in detail the process of rapid cloud cooling after the passage of a shock front, to test high abundances of O4+, O5+ and O6+ ions at low temperatures and measure them, to test existing theoretical models of FMK and to build more precise ones.
Key words: atomic processes -- supernovae: individual: Cassiopeia A -- infrared: ISM
© ESO 2008