New beryllium observations in low-metallicity stars

We present observations of the Be II 313.0 nm resonance doublet in 14 halo and old disk stars with metallicities ranging from [Fe/H]=-0.4 to about -3.0 obtained with the CASPEC spectrograph of the ESO 3.6m telescope at a FWHM about 8.6 km/s resolution. Abundances are derived by means of the synthetic spectra technique employing Kurucz (1993) atmospheric models, with enhanced alpha-elements and no overshooting. The derived abundances together with those available in literature show that for -2.7 < [Fe/H] < -0.8 Be correlates linearly with iron [Be] proportional to 1.07(+/- 0.08)[Fe/H], giving strength to previous results. However, a steeper correlation is still possible at metallicities lower than [Fe/H]<-1.4 with [Be] proportional to 1.6(+/- 0.44)[Fe/H]. When iron is replaced with oxygen, Be is found tracking closely oxygen up to solar values, without signs of breaking in correspondence of the onset of the Galactic disk. No evidence of intrinsic dispersion is found, ought to the large errors involved in the Be abundance determinations, but for three stars (HD 106516, HD 3795, HD 211998) a significant upper limit in the Be abundance can be placed at about 1 dex below the mean trend of the Be-Fe relation. For such stars non conventional mixing is required to explain Be depletion. Be observations can be used to discriminate strongly Li-depleted stars. These are the stars which show less Li than that expected by high energy cosmic rays production as deduced from Be observations. The available Be observations imply that some of the stars which contribute to the scatter in the Li-Fe diagramme are Li-depleted stars.