An abundance analysis of the symbiotic star CH Cygni

¹ N. Copernicus Astronomical Center, ul. Rabiańska 8, 87-100 Toruń, Poland e-mail: schmidt@ncac.torun.pl
² Institute of Atomic Physics and Spectroscopy, University of Latvia, Raiņa bulvāris 19, 1586 Rīga, Latvia e-mail: zacs@latnet.lv
³ N. Copernicus Astronomical Center, ul. Bartycka 18, 00716 Warsaw, Poland e-mail: mikolaj@camk.edu.pl
⁴ National Optical Astronomy Observatory, PO Box 26732, Tucson, AZ 85726, USA e-mail: hinkle@noao.edu

Received: 9 April 2005
Accepted: 12 September 2005

Abstract

The photospheric abundances for the cool component of the symbiotic star 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 (T_eff = 3100 K, (cgs), 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 ¹²C/¹³C and ¹⁶O/¹⁷O are close to the mean values for single M giants that have experienced the first dredge-up. A reasonable explanation for the absence of barium star-like chemical peculiarities seems to be the high metallicity of CH Cyg. The emission line technique was explored for estimating CNO ratios in the wind of the giant.