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 II 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 star by Gonzalez & Lambert, and of red giants in M5 by Sneden et al. The analysis is based on six spectra obtained during three different phases of the star's pulsational cycle. Oxygen is depleted, and sodium is enhanced, while the "α" elements Mg, Si, Ca, and Ti are enhanced by about 0.3 dex. Most interesting, lithium is detected, with log (Li) ≈ +1.8, suggesting the production of lithium and its rapid transport to the surface. Zinc and silicon abundances are normal with respect to iron and calcium, suggesting that depletion onto dust grains during the AGB stage has not affected the star's abundances. The neutron-capture elements show ratios consistent with a nearly pure r-process origin. This r-process dominance is probably unrelated to the production of lithium, since the cluster's red giant branch stars show a similar pattern. Nonetheless, it appears that some low-mass, metal-poor stars do not solely destroy lithium in the course of their normal evolution.