CHEMICAL-COMPOSITION OF THE METAL-POOR CARBON STAR HD-187216

We have derived C, N and metal abundances for the metal-deficient late -type (C3,3CH) CH giant HD 187216 (alpha(2000.0) = 19(h)24(m)18.6(s), delta(2000.0) = +85 degrees 21'56.5''). The oxygen abundance was fixed at log A(O) = 7.0, assuming that it follows the trend of oxygen overa bundance relative to iron found in halo stars in general. New model at mospheres of metal-poor carbon stars were calculated with continuum op acity sources and molecular lines of CO, CN, C-2, HCN, C2H2 and C-3. N umerical experiments with various assumed input parameters, such as ef fective temperature, T-eff, surface gravity, log g, microturbulent vel ocity, xi(t), and dissociation energy of the CN molecule, D-0(CN), wer e performed when constructing the model atmospheres and calculating th e synthetic spectra. The atmospheric model with T-eff = 3500 K, log g = 0.4, xi(t) = 3 km s(-1) C-12/C-13 = s and D-0(CN) = 7.9 eV was adopt ed for abundance analysis. The star was found to be extremely metal-de ficient, [Fe/H] = -2.48. The carbon abundance is log A(C) = 7.33, the nitrogen abundance is log A(N) = 5.60 corresponding to [C/Fe] = +1.3, [N/Fe] = +0.2, and [N/C] = -1.1. The carbon isotopic abundance ratio i s C-12/C-13 = 7.0. The abundances of heavy elements produced in the s- process are larger than in early-type CH stars. The ratio of overabund ance of heavier s-process elements to that of lighter ones, [hs/1s] = 1.0, points to a very high neutron exposure in a single irradiation ev ent. Search for binarity of HD 187216 has failed, and the star can be an intrinsic asymptotic giant branch (AGB) carbon star with some simil arities to the C stars in the dwarf galaxies. If the CH characteristic s are due to mass transfer it is most likely oxygen-rich material that has been donated. The star possesses both a low nitrogen abundance an d a low C-12/C-13 ratio, in conflict with the standard stellar evoluti on theory.