CH CygType: Z AndromedaeAAVSO lightcurve (2020 )AAVSO lightcurve (index)Symbiotic variables of the Z Andromedae type are close binaries consisting of a hot star, a star of late type, and an extended envelope excited by the hot star's radiation. The combined brightness displays irregular variations with amplitudes up to 4 mag. in V. A very inhomogeneous group of objects. Semi-regular variables, which are giants or supergiants of intermediate and late spectral types showing noticeable periodicity in their light changes, accompanied or sometimes interrupted by various irregularities. Periods lie in the range from 20 to >2000 days, while the shapes of the light curves are rather different and variable, and the amplitudes may be from several hundredths to several magnitudes (usually 1-2 mag. in V) AAVSO Alert 639: 3 July 2018CH Cyg recovered in early August 2018 from the fading episode described below. However, ongoing coverage is extremely important, with V and particularly B being given priority over Rc and Ic. As always, visual observations are requested and encouraged. - Elizabeth O. Waagen, November 29, 2018 3 July 2018: The symbiotic variable CH Cyg is undergoing a fade that began on 25 June. Multicolor photometry is requested; V and particularly B should take priority over Rc and Ic. Observations made two to three times a week are sufficient; time series observations are not needed. Visual observations are also requested and encouraged. Spectroscopy would be very welcome and appreciated. Coverage should continue throughout the observing season. The AAVSO has had an ongoing campaign on CH Cyg for Dr. Margarita Karovska (Harvard- Smithosonian Center for Astrophysics) underway for the past several years (links below). These fading events are of particular interest when the system fades most in B, as is currently happening. There is not a long history of B observations of CH Cyg, so it is essential to have good coverage in B throughout the fading episode and afterwards. Information on the CH Cyg campaign may be found in: AAVSO Alert Notice 454 and AAVSO Special Notices #267, #268, #294, #320, and #417.