CONSTRAINTS ON THE USE OF BE-I LINES FOR DERIVING BERYLLIUM ABUNDANCES IN LATE-TYPE DWARF STARS

Beryllium is a key element for constraining mixing processes taking pl ace in the interiors of late-type dwarfs, and this paper investigates the use of neutral beryllium lines to obtain reliable abundances. The best candidate, among other Be I features, is the Be-9 I lambda 2348.6 09 Angstrom resonance line. Its spectral location, well below the Eart h's UV transmission limit, implies its observation with satellites (at the present time the Hubble Space Telescope -HST-). Synthetic spectra of this region, with different beryllium abundances, were computed fo r a cool star previously studied using the Be II lambda 3131.065 Angst rom line (which provided only an upper limit to its beryllium abundanc e). The low sensitivity shown by the feature associated with the Be I line to changes as large as three orders of magnitude in the beryllium abundance, the poor knowledge of the atomic and molecular line-data i n the relevant spectral region, and the limited signal-to-noise ratios associated with the restricted exposure times of the HST prevent the use this line for abundance analysis purposes. This result is generall y applicable to dwarf stars in the effective temperature range 4800-58 00 K. A detailed knowledge of the lines present in the spectral region considered would be essential for improving this situation. However, a similar improvement in the data for the lines surrounding the Be II lambda 3131.065 Angstrom line (which is more isolated and can be obser ved from ground-based telescopes) would be probably much more useful.