CH Cygni in the transition to its cool phase

Abstract

U, B, V-observations, supplemented by spectrophotometric measurements of the symbiotic variable CH Cyg in the years 1982 to 1984 show that the star has reached its ‘blue maximum phase’ of its recent outburst in the first half of 1984. From end of July, 1984 on the object underwent a considerable drop in brightness and an increase of its colour indices, and which indicates that it was on the way to its cool phase. Also the spectroscopic observations show that the ‘blue’ continuum still observed at the beginning of July, 1984 has disappeared in October–November, 1984 and the strong absorption features, typical for a M-type giant were re-appearing. A remarkable intensity increase of the emission features, especially those of the Balmer lines, took place within this time interval. The rapid flickering variations of CH Cyg had also reached the culmination amplitude in July, 1984. There seem to be three periodicities present in these flickering variations with cycle lengths of 7.7 min, 21 min, and 60 min. Though these observational findings would be consistent with the M-type blue subdwarf component binary model with mass flow from the M6-III giant to the companion, the genuine binary nature of CH Cyg could not be established beyond doubt.