Abstract
We secured the high dispersion spectra of the symbiotic star CI Cyg. The HI, HeI, and HeII line profiles were analyzed using the relatively long exposure data including 1800 sec (Sep. 12, 1998, phase=0.90), 3600 sec (Aug. 12, 2002, ${\phi}=0.47$), and 1800 sec (Oct. 21, 2009, ${\phi}=0.54$). Although a minor outburst was reported in 2008, our three observation periods were generally known to be quiescent in earlier photometric studies. With the help of hydrodynamic simulations, we identified the two emission zones responsible for the blue- and red-shifted line components: (a) an accretion disk around a hot white dwarf star which consists of the outer cool HeI emission zone and the inner hot HeII emission part, and (b) a high density zone near the inner Lagrangian point responsible for the HeI line flux variation and the broadening of its line profile. The HeII line fluxes indicate that the HeII emission zone of the accretion disk is relatively stable, implying a constant gas inflow from the giant star throughout the quiescent period. The 2002 HeI data showed that the notable mass flow activity through the inner Lagrangian point occurred during this period and its flux intensity became strongest, whereas the HeII line width in the same period indicates that its flow activity forced the accretion disk to expand. The [OIII] lines were observed in 1998 but not detected in 2002 and 2009, implying the disappearance of the low density zone. Based on our kinematical studies upon the line profiles, we conclude that CI Cyg was stable in 1998 among the three observation periods selected in this research.