Dust formation in binaries with OB and WR components in a two-phase stellar-wind model

We describe the formation of carbon dust in binary systems with hot compone nts as a result of the collisions of clouds in a two-phase stellar-wind mod el. Calculations are made fur the well studied system WR 140. The collision s lead to the formation of composite clouds and shock waves, with the tempe rature at the shock front equal to about 3 x 10(8) K along both sides of th e interface boundary. During isobaric deexcitation to (0.5-0.7) x 10(4) K, the cloud density increases by a factor of several thousand; its thickness in the direction of the shock decreases by the same factor. After deexcitat ion, the hydrogen inside the composite cloud is in its atomic state, while the carbon remains ionized. The deexcitation is followed by expansion of th e cloud, which moves away from both stars. During the first 10(6) st its th ickness remains relatively small, so that the expansion is one-dimensional. The radiation field inside the cloud decays, resulting in the recombinatio n of the carbon. Further expansion of the cloud leads to adiabatic cooling, and the formation of dust particles becomes possible. After the dimensions of the cloud have become roughly the same in all directions, its expansion is isotropic, so that it becomes transparent within approximately 10(6) s, and the dust is heated to (1.0-1.4) x 10(3) K, observed as an IR "flare." The time required for the cloud to move from the exciting star and heat the dust is comparable to the observed delay in the increased IR emission rela tive to the time of periastron. (C) 2001 MAIK "Nauka/Interperiodica".