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Modeling of atmospheres of the brightest stars belonging to the Cyg OB2 association

We present the results of modeling of the spectrum of the brightest stars belonging to the Cyg OB2 association - #7 (O3If*) and #11 (O5Ifc). #7 is one of the hottest stars in our Galaxy, while #11 belongs to the spectral class Ofc, which was recently introduced and yet small in numbers (Walborn et al., 2010). We determine the physical properties and chemical composition of their atmosphere using CMFGEN code. The atmosphere of #7 reveals an excess of nitrogen X(N*)/X(Nsun) = 3.2 and the carbon and oxygen deficiency X(C*)/X(Csun) = 0.08, X(O*)/X(Osun) = 0.09, while the atmosphere of #11 is enriched with carbon X(C*)/X(Csun)=1 and silicon X(Si *)/X(Si sun)=2.