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The model atmospheres (the atmospheres were computed by M.A.Barstow using computer code originally developed by G.A.Williams, J.Brooker and A.R.King) used here are:
; 
) and
;
Models (i) and (ii) are representative models for hot DA white dwarfs
( 
K) with different compositions. Care should always be
taken when interpreting the results given in
Figures 12.6 
and 12.7 since
XUV fluxes are extremely sensitive to He
abundances which can differ markedly from these models in individual objects.
For each model atmosphere, and for each of the scientific filters as listed in
Table 5.3 ,
Figures 12.6 and 12.7
show the expected WFC count rate as a function of temperature
for a set of column densities 
varying from 
to
cm 
.
For these model atmospheres the plots are normalized to a V-magnitude
, thus the
estimated WFC count rate can be determined simply by scaling the
conversion factor (CF) to the V-magnitude
of the source in question, 
, i.e., 
.