Context : As of today , over 50 planetary systems have been discovered in binary star systems , some of which have binary separations that are smaller than 20 AU .
In these systems the gravitational forces from the binary have a strong influence on the evolution of the protoplanetary disk and hence the planet formation process .

Aims : We study the evolution of viscous and radiative circumstellar disks under the influence of a companion star .
We focus on the eccentric \gamma Cephei and \alpha Centauri system as examples and compare disk quantities such as disk eccentricity and precession rate to previous isothermal simulations .

Methods : We performed two-dimensional hydrodynamical simulations of the binary star systems under the assumption of coplanarity of the disk , host star and binary companion .
We used the grid-based , staggered mesh code FARGO with an additional energy equation to which we added radiative cooling based on opacity tables .

Results : The eccentric binary companion perturbs the disk around the primary star periodically .
Upon passing periastron , spirals arms are induced that wind from the outer disk towards the star .
In isothermal simulations this results in disk eccentricities up to e _ { \mathrm { disk } } \approx 0.2 , but in more realistic radiative models we obtain much smaller eccentricities of about e _ { \mathrm { disk } } \approx 0.04 - 0.06 with no real precession .
Models with varying viscosity and disk mass indicate that disks with less mass have lower temperatures and higher disk eccentricity .

Conclusions : The fairly high disk eccentricities , as indicated in previous isothermal disk simulations , implied a more difficult planet formation in the \gamma Cephei system caused by the enhanced collision velocities of planetesimals .
We have shown that under more realistic conditions with radiative cooling the disk becomes less eccentric and thus planet formation may be made easier .
However , we estimate that the viscosity in the disk has to very low , with \alpha \lesssim 0.001 , because otherwise the disk ’ s lifetime will be too short to allow planet formation to occur along the core instability scenario .
We estimate that the periodic heating of the disk in eccentric binaries will be observable in the mid-IR regime .