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Dramatic deficiencies of Li in the mid-F dwarf stars of the Hyades cluster were discovered by Boesgaard & Tripicco. Boesgaard & King discovered corresponding, but smaller, deficiencies in Be in the same narrow temperature region

The surface content of lithium (Li) and beryllium (Be) provides insight into the mixing and circulation mechanisms in stellar interiors. The old open cluster, M67, has been well-studied for Li abundances in both main-sequence and evolved stars. The Be abundances give us a probe to a deeper level in stars. We have taken high-resolution spectra with Keck I with HIRES to determine Be abundances along the subgiant branch of M67, where there are dramatic depletions of Li. These subgiants range in mass from 1.26 to 1.32 M ⊙ and have evolved from main-sequence stars that would have occupied the region of the Li–Be dip found in younger clusters. Lithium abundances have been adjusted to the same scale for 103 stars in M67 by Pace et al. The more massive stars—now the coolest and furthest-evolved from the main sequence—show a drop in Li by a factor of 400 across the subgiant branch. Our new Be abundances also show a decline, but by a factor of ∼50. The two elements decline together with Li showing a steeper decline in these subgiants than it does in the Li–Be dip stars. The relative decline in Be abundance compared to Li is remarkably well fit by the models of Sills & Deliyannis, made specifically for the subgiants in M67. Those models include the effects of mixing induced by stellar rotation. These M67 subgiants show the effects of both main-sequence depletion and post-main-sequence dilution of both Li and Be.

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The surface abundances of the light elements lithium (Li) and beryllium (Be) reveal information about the physical processes taking place in stellar interiors. The investigation of the amount of these two elements in stars in open clusters shows the effect of age on those mechanisms. We have obtained spectra of both Li and Be in main-sequence stars in NGC 752 at high spectral resolution and high signal-to-noise ratios with HIRES on the Keck I telescope. In order to make meaningful comparisons with other clusters, we have determined the stellar parameters on a common scale. We have found abundances of Li and Be by spectral synthesis techniques. NGC 752 is twice the age of the well-studied Hyades. We find that (1) the Li dip centered near 6500 K is wider in NGC 752, having expanded toward cooler temperatures; (2) the Be dip is deeper in the older NGC 752; (3) the Li “peak” near 6200 K is lower by about 0.3 dex; (4) although there is little Be depletion in the cooler stars, it is possible that Be may be lower in NGC 752 than in the Hyades; and (5) the Li content in both clusters declines with decreasing temperature, but there is less Li in NGC 752 at a given temperature by ∼0.4 dex. These differences are consistent with the transport of the light-element nuclei below the surface convection zone as predicted by theory. That connection to rotational spin-down is indicated by the pattern of rotation with temperature in the two clusters.