Lithium and r-process abundances in the Population II Cepheid M5 V42

We report the results of an abundance analysis of the 25.7 day Population I I Cepheid V42 in the globular cluster M5. V42 is probably a post-asymptotic giant branch (AGB) star, in its final crossing of the H-R diagram. We find [Fe/H] = -1.22, in excellent agreement with a similar analysis of this sta r by Gonzalez & Lambert, and of red giants in M5 by Sneden et al. The analy sis is based on six spectra obtained during three different phases of the s tar's pulsational cycle. Oxygen is depleted, and sodium is enhanced, while the "alpha" elements Mg, Si, Ca, and Ti are enhanced by about 0.3 dex. Most interesting, lithium is detected, with log epsilon(Li) approximate to +1.8 , suggesting the production of lithium and its rapid transport to the surfa ce. Zinc and silicon abundances are normal with respect to iron and calcium , suggesting that depletion onto dust grains during the AGE stage has not a ffected the star's abundances. The neutron-capture elements show ratios con sistent with a nearly pure r-process origin. This r-process dominance is pr obably unrelated to the production of lithium, since the cluster's red gian t branch stars show a similar pattern. Nonetheless, it appears that some lo w-mass, metal-poor stars do not solely destroy lithium in the course of the ir normal evolution.