SIMBAD references

High resolution (R≃110000), very high S/N spectra centered on the 6707.8 Å LiI line have been obtained with the ESO Coude Echelle Spectrometer for five, metal-poor (-0.8<[Fe/H]←0.6) disk stars in the turnoff region of the HR-diagram. The instrumental and stellar atmospheric line broadening have been determined from two unblended iron lines and used in a model atmosphere synthesis of the profile of the LiI line as a function of the lithium isotope ratio. This has led to a detection of ⁶Li in HD 68284 and HD 130551 with ⁶Li/⁷Li≃0.05, whereas the other stars, HR 2883, HR 3578 and HR 8181, have ⁶Li/⁷Li close to zero. By comparing T_eff-values and absolute magnitudes based on Hipparcos parallaxes with recent stellar evolutionary tracks, the masses of the stars have been derived. It is shown that the two stars with ⁶Li present have a significantly higher mass, M/M☉ ≃1.05, than the other three stars for which values between 0.85 and 1.0 M☉ are obtained. The results are discussed in terms of models for the galactic evolution of the light elements and depletion of the lithium isotopes in stellar envelopes. It is shown that the measured ⁶Li abundances are in agreement with standard cosmic ray production of ⁶Li in the galactic disk and a moderate depletion (0.5dex) in the stars. Recent models for the evolution of ⁶Li including α+ α fusion reactions and predicting a high lithium isotopic ratio, ⁶Li/⁷Li≃0.3 at [Fe/H]=-0.6, require a high degree of ⁶Li depletion (≃1.0dex) to fit the observations. Furthermore, these models imply a ⁷Li abundance about 0.2dex higher than observed for metal-poor disk stars.