Li Evolution among Stars of Low/Intermediate Mass: the Metal-deficient Open Cluster NGC 2204

Abstract We have analyzed high-dispersion spectra in the Li 6708 Å 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 asymptotic giant branch 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 M ☉ . Despite having the same isochronal age as the more metal-rich NGC 2506, the luminosity distribution of red giants reflects a younger morphology similar to NGC 7789, possibly indicating a deeper impact of metallicity 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 place of the cluster within Galactic A (Li) evolution is discussed.