Spectrophotometric Monitoring of the Activity of the Symbiotic Star CH Cyg from 2008 to 2018

Abstract

Based on spectrophotometric observations, we have studied the variable activity of the symbiotic star CH Cyg from 2008 to 2018. The activity of the star was accompanied by a periodic increase of the flux in continuum and spectral lines. In the period of its activity, in both 2015 and 2018, absorption components appeared in the profiles of emission lines. The shape and radial velocity of the absorption components changed within a day. The maximum radial velocity of the absorption components was about $-2000$ km s${}^{-1}$. By modeling the observed spectral energy distribution, we have established that in the active state the luminosity and radius of the warm pseudo-photosphere of the symbiotic star increased by dozens of times, reaching $L_{\textrm{WD}}=88.14L_{\odot}$ and $R_{\textrm{WD}}=6.77R_{\odot}$, respectively, at maximum in 2018, and the source of activity of the symbiotic star is accretion onto a white dwarf from a red giant of spectral type M8III. The accretion rate at the maximum luminosity of the pseudo-photosphere has been estimated to be $\dot{M}_{\textrm{acc}}\sim 4.7\times 10^{-8}M_{\odot}$ yr${}^{-1}$. We have found a correlation between the TiO 6144 and 7125 molecular bands and the $R$ brightness of the star, which suggests that a period of 750 days may be the pulsation period of the cool component, and, hence, we have concluded that the pulsations of the cool component at periastron or at a phase close to the periastron can provide an additional inflow of matter accreting onto the white dwarf. Thus, we have concluded that a variable mass accretion rate onto the white dwarf is responsible for the photometric variability of the symbiotic star. We show that 2015 and 2018 were the most active years for this star.