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AE Aquarii is a very peculiar bright nova-like cataclysmic variable in which a
magnetized white dwarf accretes matter from a K5-dwarf: it belongs to the
Intermediate Polar group although in many respects AE Aqr stands out uniquely
in comparison to most of these systems and it indicates several features of
extreme physical conditions. It emits over a wide energy range, from TeV gamma
to radio frequencies, and it displays a wide range of variability on different
timescales.
It is the strongest radio emitter among cataclysmic variables, its
radio radiation is always detectable, either flares as or as quiescence. From
one day to another, its average flux density can vary by more than a factor
two. But its time-averaged flux increases from 1.4 to 394 GHz (21 cm to 761
microns) following a rather constant power-law. By analogy with the X-ray
binary Cyg X-3, Bastian, Dulk and Chanmugam (1988, hereafter BDC) interpreted
AE Aqr's non-thermal radio emission as the superposition of several plasma
clouds' synchrotron radiation. In this model the initial turnover frequency of
a given plasmoid is directly related to the initial magnetic field strength Bo
in this plasmoid: the detection at 761 microns implies that Bo > 300 G.
In order to estimate directly the value of Bo and to restrict the
values of other parameters of the plasmoids, which will significantly
constrain the BDC model, we want to measure AE Aqr's flux at 90 and 160
microns. This will allow to measure the turnover frequency of the
radio-to-far-infrared spectrum and/or to study the unknown optically thin part
of this spectrum. Only ISO can provide measurements at such long wavelength
since IRAS results imply too high upper limits on the far infrared flux.