High-Resolution Spectroscopic Observations of Four Yellow-Type Symbiotic Stars: CD-43°14304, Hen 3-1213, Hen 3-863, and StHα 176

We report on the analysis of high-resolution optical spectra of four symbiotic stars CD-43°14304, Hen 3-863, Hen 3-1213, and StHα176. The chemical composition of the atmospheres of the investigated stars shows that they are all metal-poor K giants with metallicities around [Fe/H] ≈ -1.0. All stars show an enrichment of the elements created by slow neutron-capture reactions. The luminosities obtained for the symbiotic star CD-43°14304 and probably for Hen 3-1213 are below those of the asymptotic giant branch (AGB) stars that started helium-burning (via thermal pulses) and became self-enriched in the neutron-capture elements. Therefore, their abundance peculiarities are due to mass transfer from the previous thermally pulsing AGB star (now the white dwarf), overabundant in s-process elements. For the stars Hen 3-863 and StHα176, the uncertainties due to the distance (and interstellar absorption as well) prevent a reliable determination of the luminosity. The heavy-element abundance distribution of these four analyzed symbiotics is similar to that of the three symbiotics previously analyzed (AG Dra, BD-21°3873, and Hen 2-467). Finally, their general abundance pattern follows the halo standard abundance.

Based on the observations made with the 2.2 m telescope at the European Southern Observatory (La Silla, Chile).