First detections of the cataclysmic variable AE Aquarii in the near to far infrared with ISO and IRAS: Investigating the various possible thermal and non-thermal contributions

M. Abada-simon, J. Casares, S. Eyres, R.P. Fender, S. T. Garrington, O. De Jager, N. Kuno, I. G. Martínez-pais, D. De Martino, H. Matsuo, M. Mouchet, G. G. Pooley, G. Ramsay, A. Salama, B. Schulz, A. Evans

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We have used ISO to observe the Magnetic Cataclysmic Variable AE Aquarii in the previously unexplored range from 4.8 μm up to 170 μm in the framework of a coordinated multi-wavelength campaign from the radio to optical wavelengths. We have obtained for the first time a spectrum between 4.8 and 7.3 μm with ISOCAM and ISOPHOT-P: the major contribution comes from the secondary star spectrum, with some thermal emission from the accretion stream, and possibly some additional cyclotron radiation from the post-shock accretion material close to the magnetised white dwarf. Having reprocessed ISOPHOT-C data, we confirm AE Aqr detection at m and we have re-estimated its upper limit at 170 μm. In addition, having re-processed IRAS data, we have detected AE Aqr at 60 μm and we have estimated its upper limits at 12, 25, and 100 μm. The literature shows that the time-averaged spectrum of AE Aqr increases roughly with frequency from the radio wavelengths up to m; our results indicate that it seems to be approximately flat between ~761 and m, at the same level as the 3σ upper limit at 170 μm; and it then decreases from m to m. Thermal emission from dust grains or from a circum-binary disc seems to be very unlikely in AE Aqr, unless such a disc has properties substantially different from those predicted recently. Since various measurements and the usual assumptions on the source size suggest a brightness temperature below 109 K at mm, we have reconsidered also the possible mechanisms explaining the emission already known from the submillimetre to the radio. The complex average spectrum measured from m to the radio must be explained by emission from a plasma composed of more than one “pure” non-thermal electron energy distribution (usually assumed to be a power-law): either a very large volume (diameter ≥ 80 times the binary separation) could be the source of thermal bremsstrahlung which would dominate from m to the ~millimetre, with, inside, a non-thermal source of synchrotron which dominates in radio; or, more probably, an initially small infrared source composed of several distributions (possibly both thermal, and non-thermal, mildly relativistic electrons) radiates gyro-synchrotron and expands moderately: it requires to be re-energised in order to lead to the observed, larger, radio source of highly relativistic electrons (in the form of several non-thermal distributions) which produce synchrotron.

Original languageEnglish
Pages (from-to)1063-1077
JournalAstronomy and Astrophysics
Issue number3
Publication statusPublished - 1 Apr 2005


  • stars: novae, cataclysmic variables
  • infrared: stars
  • radio continuum: stars
  • stars: flare
  • radiation mechanisms: thermal
  • radiation mechanisms: non-thermal


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