Optical and near-infrared recombination lines of oxygen ions from Cassiopeia A knots
Abstract
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 μm. 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.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- June 2008
- DOI:
- 10.1051/0004-6361:200809579
- arXiv:
- arXiv:0802.1911
- Bibcode:
- 2008A&A...484..755D
- Keywords:
-
- atomic processes;
- supernovae: individual: Cassiopeia A;
- infrared: ISM;
- Astrophysics
- E-Print:
- 18 pages, 22 figures, version accepted by A&