GALACTIC EVOLUTION OF BERYLLIUM .1. NLTE EFFECTS AND ACCURACY OF BERYLLIUM ABUNDANCES IN METAL-POOR STARS

We have investigated in detail the uncertainties in deriving beryllium abundances for metal-poor stars from the Bell resonance doublet at la mbda 3131 Angstrom. These uncertainties are related to the quality of the observations, the physical data used, and the adopted stellar para meters. We have taken into account the NLTE effects on the lines forma tion for the Sun and a sample of six stars with metallicities in the r ange -0.4 greater than or equal to [Fe/H] greater than or equal to -2. 7. NLTE nd LTE calculations give nearly the same equivalent widths for the Sun, confirming the previous results of Chmielewski et al. (1975) . The extension of the NLTE analysis to metal-poor stars indicates tha t the absolute NLTE corrections to the beryllium abundances are lower than 0.1 dex. The six selected metal-poor stars have been previously o bserved by other authors, and show a dispersion of similar to 0.2 - 0. 5 dex in their Be abundances (which can be as large as similar to 1 de x when including the error bars). Our analysis of these stars provides consistent abundances with uncertainties in the range 0.2 - 0.3 dex, which are basically related to the errors in the adopted stellar param eters (mainly surface gravity). These uncertainties and NLTE correctio ns less than or similar to 0.1 dex should be taken into account when u sing LTE beryllium abundances for primordial nucleosynthesis and Galac tic chemical evolution studies.