Parameters of the dust envelope of the symbiotic star CH Cygni

Abstract

The brightness and color variations of the symbiotic star CH Cygni are studied, and its stationary, spherically symmetric, extended dust envelope is modeled based on long-term UBVRJHKLM photometry, the mid-IR spectral energy distribution (7–23 µm), and far-IR fluxes measured by IRAS and ISO. The existence of a hot dust envelope, detected earlier in the near IR, is confirmed; the optical depth of the envelope has probably increased with time. Model fits to the IRAS and ISO data indicate that the V-band optical depth increased from 0.22 to 0.41 due to dust density enhancement during the 14 years between the observations by the two spacecraft. The mass-loss rate, gas-expansion velocity at the outer boundary of the envelope, and upper limit of the mass of the central source of emission are estimated assuming that the stellar wind of the system is driven by the pressure of the red giant's radiation on the dust, with subsequent momentum transfer to the gaseous medium.