A Detailed Analysis of the High-Resolution Spectra of the Symbiotic = BD-21degrees 3873

We report the detailed spectroscopic analysis of the high-resolution optical spectra of the cool component of the symbiotic star BD-21° 3873. Its atmospheric and kinematic parameters identify it as a typical halo giant star, with the exception of a 0.45 dex excess of the heavy neutron-capture elements. Its luminosity is insufficient for an AGB star which could have commenced shell helium burning and become self-enriched in the neutron-capture elements. Its heavy element excess is thus ascribed to the barium phenomenon, in which the secondary component accreted matter from the primary one (now the white dwarf) when it was a TP-AGB star self-enriched in the s-process elements. This object therefore provides yet another link between the symbiotic systems and the barium stars. We have obtained as a novel result a deficiency of Cu in the photosphere of BD-21° 3873, which could be related to the depletion of this element by the operation of the neutron-capture synthesis during the TP-AGB phase of the former primary component.