Spectroscopic Study of the Symbiotic Star CI Cyg

Abstract

Department of Earth Science Education (Astronomy), Chungbuk National University,Chungbuk 361-763, KoreaAbstract: We secured the high dispersion spectra of the symbiotic star CI Cyg. The HI, HeI, and HeII line profiles wereanalyzed using the relatively long exposure data including 1800 sec (Sep. 12, 1998, phase=0.90), 3600 sec (Aug. 12,2002, φ=0.47), and 1800 sec (Oct. 21, 2009, φ=0.54). Although a minor outburst was reported in 2008, our threeobservation periods were generally known to be quiescent in earlier photometric studies. With the help of hydrodynamicsimulations, we identified the two emission zones responsible for the blue- and red-shifted line components: (a) anaccretion disk around a hot white dwarf star which consists of the outer cool HeI emission zone and the inner hot HeIIemission part, and (b) a high density zone near the inner Lagrangian point responsible for the HeI line flux variation andthe broadening of its line profile. The HeII line fluxes indicate that the HeII emission zone of the accretion disk isrelatively stable, implying a constant gas inflow from the giant star throughout the quiescent period. The 2002 HeI datashowed that the notable mass flow activity through the inner Lagrangian point occurred during this period and its fluxintensity became strongest, whereas the HeII line width in the same period indicates that its flow activity forced theaccretion disk to expand. The [OIII] lines were observed in 1998 but not detected in 2002 and 2009, implying thedisappearance of the low density zone. Based on our kinematical studies upon the line profiles, we conclude that CI Cygwas stable in 1998 among the three observation periods selected in this research.Keywords: spectroscopy, line profile, symbiotic star, CI Cyg, SPH simulation.