Parameters of the dust envelope of the symbiotic star CH Cygni

The brightness and color variations of the symbiotic star CH Cygni are stud ied, and its stationary, spherically symmetric, extended dust envelope is m odeled based on long-term U BV RJHKLM photometry, the mid-IR spectral energ y distribution (7-23 mum), and far-IR fluxes measured by WAS and ISO. The e xistence of a hot dust envelope, detected earlier in the near IR. is confir med; the optical depth of the envelope has probably increased with time. Mo del fits to the IRAS and ISO data indicate that the V-band optical depth in creased from 0.22 to 0.41 due to dust density enhancement during the 14 yea rs between the observations by the two spacecraft. The mass-loss rate, gas- expansion velocity at the outer boundary of the envelope, and upper limit o f the mass of the central source of emission are estimated assuming that th e stellar wind of the system is driven by the pressure of the red giant's r adiation on the dust, with subsequent momentum transfer to the gaseous medi um. (C) 2001 MAIK "Nauka/Interperiodica".