Variations of the parameters of the dust envelope of the symbiotic star CH Cygni

Abstract

The results of JHKLM photometry of the symbiotic star CH Cyg are presented. These demonstrate that, in Autumn 2006, the state of maximum near-IR brightness observed in 2003 2006 was replaced by a sharp brightness decline in all wavebands. One possible explanation is a sharp increase in the density of circumstellar dust envelope. The JHKLM photometry data together with ISO far-IR flux measurements are used to calculate spherically symmetric dust-envelope models for the maximum and minimum brightness states. The optical depth, expansion rate, and mass-loss rate of the envelope are calculated for both states, as well as an upper limit for the mass of the central source. Comparison with earlier models suggests that the rate of growth of the envelope optical depth and the mass-loss rate by the star are accelerating with time.