SIMBAD references

We study the effects of resonance scattering in the X-ray spectra of supernova remnants. We show the importance of these effects using the ASCA X-ray spectrum of Cas A as an example. In particular the abundances derived in the common optically thin approximation can be off by a factor of 2 in the case of oxygen. Also in other supernova remnants similar effects are expected to be important. With future high-resolution missions like AXAF and XMM it is necessary to incorporate resonance scattering in the spectral analysis tools.