Nice example of co-operation of visual and electronic observations. YY Her is symbiotic variable showing periodic variations connected with the orbital motion. Porb = 589.5 d. Sometimes the outbursts occurs. See the long term light curve below:
From the first sight one can say that there is a lack of CCD measurements recently. Mainly visual data give us the information about current deep minimum. The detailed light curve is in the next figure:
Of course more information about the physics can be obtained from spectroscopic observations. Unfortunately the object is relatively faint. So difficult to take good spectra with small telescope. Only three spectra during the last cycle can be found in the ARAS database. See the following pictures.
One can clearly see major contribution of the cool component during the low state. The typical broad TiO bands of the red giant are more pronounced on the right side = longer wavelengths of the spectra. Second important feature are hydrogen emission lines. Mainly H-beta is weaker in the low state. These observations suggests that during the minimum brightness the red giant is obscuring some hot source of light. The hot component or the nebula. This “eclipsing model” was already proposed by Hric et al. (2006) as an alternative to the explanation by Mikołajewska et al. (2002) based on the ellipsoidal effect of highly distorted red giant. So we can consider the present observations as a support of the former hypothesis.