Li Evolution Among Stars of Low/Intermediate Mass: The Metal-Deficient Open Cluster, NGC 2204

We have analyzed high-dispersion spectra in the Li 6708 Angstrom region for 167 stars within the anticenter cluster, NGC 2204. From 105 probable members, abundance analysis of 45 evolved stars produces Fe/H = -0. 40 +/- 0. 12, Si/Fe = 0. 14 +/- 0. 12, Ca/Fe = 0. 29 +/- 0. 07, and Ni/Fe = -0. 12 +/- 0. 10, where quoted errors are standard deviations. With E (B-V) = 0. 07 and (m-M) ₀ = 13. 12, appropriate isochrones provide an excellent match from the main sequence through the tip of the giant branch for an age of 1. 85 +/- 0. 05 Gyr. Li spectrum synthesis produces A (Li) below 1. 4 at the base of the red giant branch to a detectable value of -0. 4 at the tip. Six probable AGB stars and all but one red clump star have only Li upper limits. A rapidly rotating red giant is identified as a possible Li-rich giant, assuming it is a red clump star. Main sequence turnoff stars have a well-defined A (Li) = 2. 83 +/- 0. 03 (sem) down to the Li-dip wall at the predicted mass of 1. 29 solar masses. Despite the same isochronal age as the more metal-rich NGC 2506, the red giant luminosity distribution reflects a younger morphology similar to NGC 7789, possibly indicating a deeper metallicity impact on stellar structure and A (Li) than previously assumed. As in NGC 2506 and NGC 7789, the NGC 2204 turnoff exhibits a broad range of rotation speeds, making abundance estimation impossible for some stars. The cluster place within Galactic A (Li) evolution is discussed.