2000A&A...359..138T

A LTE analysis of medium resolution spectra of HD 179821 has been made. Derived atmospheric parameters of HD 179821 are T_eff=5660K, logg=-1.0 and [Fe/H]=-0.5. The position of the star in the H-R diagram, its high radial velocity (V_r=100km/s), its far infrared excess similar to PNe and its chemical composition suggest that HD 179821 is a low mass post-AGB carbon-poor supergiant and not a population I massive red supergiant. The underabundance of carbon and of the s-process element zirconium shows that HD 179821 has not gone through the third dredge-up. We emphasize the similarity of the chemical pattern of the post-AGB star HD 179821 and the C-poor halo PN DDDM-1.