Chemical abundances of giants in the S-type symbiotic systems. Metallicity, CNO abundance patterns, and S-process pollution

Cezary Galan, J. Mikolajewska, K.H. Hinkle, R.R. Joyce & B. Miszalski

Nicolaus Copernicus Astronomical Center, Poland

The elemental abundances of symbiotic giants are essential to address the role of chemical composition in the evolution of symbiotic binaries, to map their parent population, and to trace their mass transfer history. However, until quite recently photospheric chemical compositions of red giants in the S-type symbiotic systems were known only for a few cases. We report on the project in which we have greatly increased this number up to several dozens of giants, making possible a first attempt of reliable statistical analysis. Our chemical composition was derived using high-resolution (R ~ 50000), high signal-to-noise (S/N), near-IR spectra. Spectrum synthesis analysis employing standard local thermal equilibrium (LTE) and atmosphere models was used to obtain photospheric abundances of CNO and elements around the iron peak (Fe, Ti, Ni, and Sc). Our analysis revealed metallicities distributed in a wide range with maximum around slightly sub-solar, and solar metallicity. The enrichment in 14N isotope indicates that all these giants have experienced the first dredge-up, what is also confirmed by the low 12C/13C ratio, always whenever its measurement was possible. We found that the relative abundance [Ti/Fe] is large in both, the red and the yellow symbiotic systems, suggesting that it can be an intrinsic characteristic of all symbiotic giants. We will also discuss the s-process enhancement observed in some of these objects as manifested mainly by Zirconium enrichment.

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