An abundance analysis of the symbiotic star CH Cygni

Received; accepted Abstract. The photospheric abundances for the cool component of the symbiotic star CH Cyg were calculated for the first time using high-resolution near-infrared spectra and the method of of standard LTE analysis and atmospheric models. The iron abundance for CH Cyg was found to be solar, (Fe/H) = 0.0±0.19. The atmospheric parameters (Teff = 3100 K, log g = 0.0 (cgs),ξt = 2.2 km s −1 ) and metallicity for CH Cyg are found to be approximately equal to those for nearby field M7 giants. The calculated (C/H) = -0.15, (N/H) = +0.16, (O/H) = -0.07, and the isotopic ratios of 12 C/ 13 C and 16 O/ 17 O are close to the mean values for single M giants that have experienced the first dre dge-up. A reasonable explanation for the absence of barium star- like chemical peculiarities seems to be the high metallicit y of CH Cyg. The emission line technique was explored for estimating CNO ratios in the wind of the giant.