Spectroscopy of 333 NGC 6819 stars and Gaia astrometry are used to map Li evolution from the giant branch tip to 0.5 mag below the Li dip .
Isochrone comparison with [ Fe / H ] = -0.04 , based upon neural network spectroscopic analysis , produces an age of 2.25 ( 2.4 ) Gyr for E ( B - V ) = 0.16 ( 0.14 ) and ( m - M ) = 12.40 ( 12.29 ) .
Despite originating outside the Li dip , only 10 % of single subgiants/giants have measurable Li .
Above the Li dip , the limiting A ( Li ) for single stars is 3.2 \pm 0.1 but the lower range is comparable to that found within the dip .
The F-dwarf Li dip profile agrees with the Hyades/Praesepe , evolved forward .
The Li level among stars populating the plateau fainter than the Li dip is A ( Li ) = 2.83 \pm 0.16 ; the dispersion is larger than expected from spectroscopic error alone .
Comparison of Li and V _ { ROT } distributions among turnoff stars in NGC 7789 , NGC 2506 , NGC 3680 , and NGC 6819 indicates that rotational spindown from the main sequence is critical in defining the boundaries of the Li dip .
For higher mass dwarfs , spindown is likewise correlated with Li depletion , creating a second dip , but at higher mass and on a longer time scale .
The Li distribution among evolved stars of NGC 6819 is more representative of the older M67 , where subgiant and giant stars emerge from within the Li dip , than the younger NGC 7789 , where a broad range in V _ { ROT } among the turnoff stars likely produces a range in mass among the giants .