摘要：HYDRA spectra of 287 stars in the field of NGC 2506 from the turnoff through the giant branch are analyzed. With previous data, 22 are identified as probable binaries; 90 more are classified as potential non-members.Spectroscopic analyses of ∼60 red giants and slowly rotating turnoff stars using line equivalent widths and a neural network approach lead to [Fe/H]=−0.27±0.07 (s.d.) and [Fe/H]= −0.27±0.06 (s.d.), respectively. Li abundances are derived for 145 probable single-star members, 44 being upper limits. Among turnoff stars outside the Li-dip, A(Li)=3.04±0.16 (s.d.), with no trend with color, luminosity, or rotation speed. Evolving from the turnoff across the subgiant branch, there is a well-delineated decline to A(Li) ∼1.25 at the giant branch base, coupled with the rotational spindown from between ∼20 and 70 km s−1 to less than 20 km s−1 for stars entering the subgiant branch and beyond. A(Li) remains effectively constant from the giant branch base to the red giant clump level. A new member above the clump redefines the path of the firstascent red giant branch; its Li is 0.6 dex below the first-ascent red giants. With one exception, all post-He-flash stars have upper limits to A(Li), at or below the level of the brightest first-ascent red giant. The patterns are in excellent qualitative agreement with the model predictions for low/intermediate-mass stars which undergo rotation-induced mixing at the turnoff and subgiant branch, first dredge-up, and thermohaline mixing beyond the red giant bump.
关键词：open clusters and associations: individual (NGC 2506);stars: abundances;stars: evolution
