The Fe-L Complex in Cataclysmic Variables

Cataclysmic Variables (CVs) are believed to contain optically thin, X-ray emitting plasmas which cool from kT ~ 10 keV down the photospheric temperature of the underlying white dwarf. Early X-ray spectra of CVs were fitted with a single temperature bremsstrahlung model. However, with the ever improving quality of the data, increasingly sophisticated spectral models have been used to fit their X-ray spectra. Most recently, the use of multi-temperature plasma models, either with several discrete temperature components or using a differential emission measure approach, is becoming commonplace. All such efforts rely on the existing plasma codes, such as mekal, and they typically predict a strong Fe L complex emission around 1 keV, due to the kT ~ 1 keV plasma. In this poster, I will present an ASCA SIS spectral atlas of CVs focusing on the Fe-L complex region. The spectral resolution of the SIS instruments is such that, while individual features in the complex cannot be resolved, the complex as a whole is readily resolvable, if it is present in the data. The atlas will show that the strength of the Fe L complex varies considerably from system to system, and is consistent with 0 in many CVs. It is likely that the coronal approximation, inherent in the existing plasma codes, is inappropriate for CVs. I will discuss physical and astrophysical implications of this finding.