Chemical analysis of CH stars – I. Atmospheric parameters and elemental abundances

Abstract

Results from high-resolution spectral analyses of a selected sample of CH stars are presented. Detailed chemical composition studies of these objects, which could reveal abundance patterns that in turn provide information regarding nucleosynthesis and evolutionary status, are scarce in the literature. We conducted detailed chemical composition studies for these objects based on high-resolution (R ∼ 42 000) spectra. The spectra were taken from the ELODIE archive and cover the wavelength range from 3900 to 6800 Å. We estimated the stellar atmospheric parameters, the effective temperature Teff, the surface gravity log g, and the metallicity [Fe/H] from local thermal equilibrium analyses using model atmospheres. Estimated temperatures of these objects cover a wide range, from 4550 to 6030 K. The surface gravity ranges from 1.8 to 3.8, and the metallicity from −0.18 to −1.4. We report updates on elemental abundances for several heavy elements and present estimates of abundance ratios for Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu and Dy with respect to Fe. For the object HD 188650 we present the first abundance analysis results based on a high-resolution spectrum. Enhancements of heavy elements relative to Fe, which are characteristic of CH stars, are evident from our analyses for most of the objects. A parametric model-based study was performed to understand the relative contributions from the s- and r-processes to the abundances of the heavy elements.