Stellar evolution is the process by which a star changes over the course of time. We found that the relative abundance of is generally large in red symbiotic systems.Changes to stars over their lifespans Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right Chart of stellar evolution This was confirmed in a number of objects by the low 12C/ 13C ratio (5-23). The enrichment in 14N isotope, found in all these objects, indicates that the giants have experienced the first dredge-up. Our analysis reveals metallicities distributed in a wide range from slightly supersolar ( ∼ +0.35 dex) to significantly subsolar ( ∼ -0.8 dex) but principally with near-solar and slightly subsolar metallicity ( ∼ -0.4 to -0.3 dex). Spectrum synthesis methods employing standard local thermal equilibrium analysis and atmosphere models were used to obtain photospheric abundances of CNO and elements around the iron peak (Fe, Ti, Ni, and Sc). Here we present results for 24 S-type systems. This is the third in a series of papers on the chemical composition of symbiotic giants determined from high-resolution (R ∼ 50 000), near-infrared spectra. However, the number of symbiotic giants with fairly well determined photospheric composition is still insufficient for statistical analyses. 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.
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