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 \sim 60 red giants and slowly rotating turnoff stars using line equivalent widths and a neural network approach lead to [ Fe/H ] = -0.27 \pm 0.07 ( s.d . )
and [ Fe/H ] = -0.27 \pm 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 \pm 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 ) \sim 1.25 at the giant branch base , coupled with the rotational spindown from between \sim 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 first-ascent 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 .