LITHIUM ABUNDANCES IN THE SOLAR TWINS 16-CYG-A AND 16-CYG-B AND THE SOLAR ANALOG ALPHA-CEN-A, CALIBRATION OF THE 6707-ANGSTROM LI REGION LINELIST, AND IMPLICATIONS

We present high resolution (R similar to 45,000-70,000) and very high S/N (similar to 1,000) spectroscopy of the Li I 6707 Angstrom region i n each component of the binary solar twins 16 Cyg A and B, the solar a nalog alpha Cen A, and alpha Cen B. Spectra of 16 Cyg were obtained wi th the University of Hawai'i 2.2-m, McDonald Observatory 2.1-m, and Ke ck 10-m telescopes and have been independently reduced. Comparison of spectral synthesis and the 16 Cyg data, and corresponding similarly ob tained solar data, yields Li-7 abundances which show excellent concord ance between the various data sets. Despite differing in T-eff by only 35-40 K, the Li abundances of 16 Cyg A and B differ by a factor of gr eater than or similar to 4.5. The solar photospheric abundance is inte rmediate to the two values. This intermediacy indicates that the Sun, whose highly depleted photospheric Li abundance is in gross conflict w ith standard stellar models, is not an isolated anomaly in its Li abun dance evolution. A similar conclusion is reached via comparison of alp ha Cen A and metal-rich Hyades dwarfs. The difference in the 16 Cyg co mponents' abundances suggests, though does not directly establish, a s low (possibly rotationally-induced) mixing mechanism operating below t he surface convection zone in these stars. Indeed, the Li abundance di fference can be viewed as an analog to the Li abundance dispersion see n in cool stars of similar T-eff in open and globular clusters, and in Galactic field halo stars. It is possible, in principle anyway, that the low Li abundances of the Sun and 16 Cyg B with respect to 16 Cyg A may be related to the presence of a planetary companion; Li abundance s of 47 UMa, and HD 114762 might further support such a connection bet ween planets/disks, angular momentum evolution, and photospheric Li ab undances. Due to a variety of uncertainties, however, any conclusions remain tenuous and speculative at this time. Finally, as an interestin g aside, we show that current line list uncertainties in the lambda 67 07 Li region suggest that claims of very small Li-6/Li-7 ratios (less than or equal to 0.01) inferred from analysis of the solar photospheri c spectrum are overly optimistic-though not necessarily incorrect. (C) 1997 American Astronomical Society.