Two K giants with supermeteoritic lithium abundances: HDE 233517 and HD 9746

Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied. Optical spectroscopy and photometry have been obtained to determine the fundamental parameters of HDE 233517, a single K2 III with an extremely large infrared excess. The spectra yield T-eff = 4475 K, log g = 2.25, [Fe/H] = -0.37, nu sin i = 17.6 km s(-1), and a non-LTE log epsilon>(*) over bar *(Li-7) = 4.22. Photometric observations reveal low-amplitude light variability with a period of 47.9 days. Combined with other parameters, this results in a minimum radius of 16.7 R. and minimum distance of 617 pc. Comparison of spectra obtained in 1994 and 1996 show profile variations in Ha and the Na D lines indicative of changing mass loss. Optical spectra of HD 9746, a chromospherically active giant, were analyzed. The T-eff = 4400 K and revised Hipparcos-based gravity of log g = 2.30 lead to a non-LTE log epsilon>(*) over bar *(Li-7)= 3.75. The Li abundances in both stars are supermeteoritic. By the inclusion and exclusion of Li-6 in the syntheses, we show that consistent Li-7 abundances are obtained only when Li-6 is absent in the synthetic fit. This provides evidence for fresh Li-7 production and excludes both preservation of primordial Li and planetary accretion as viable scenarios for the formation of Li-rich giants. Both stars lie in close proximity to the red giant luminosity bump supporting the hypothesis that Li-7 production is caused by the same mixing mechanism that later results in CN processing and lowers the C-12/C-13 ratio to nonstandard values.