Astron. Astrophys. 319, 593-606 (1997)

New beryllium observations in low-metallicity stars ^{* **}

P. Molaro ¹, P. Bonifacio ¹, F. Castelli ^{1, 2} and L. Pasquini <sup>3

1</sup> Osservatorio Astronomico di Trieste Via G.B. Tiepolo 11, I-34131 Trieste, Italy
² Consiglio Nazionale delle Ricerche, G.N.A. Via G.B. Tiepolo 11, I-34131 Trieste, Italy
³ European Southern Observatory, Casilla 19001, Santiago 19, Chile

Received 18 April 1996 / Accepted 9 August 1996

Abstract

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 -3.0 obtained with the CASPEC spectrograph of the ESO 3.6m telescope at a FWHM 8.6   resolution. Abundances are derived by means of the synthetic spectra technique employing Kurucz (1993) atmospheric models, with enhanced -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] 1.07()[Fe/H], giving strength to previous results. However, a steeper correlation is still possible at metallicities lower than [Fe/H] -1.4 with [Be] 1.6()[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 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 diagram are Li-depleted stars. This result strongly supports the use of the upper envelope of the Li-Fe diagram to trace the Li galactic evolution, and argues for a low value for the primordial Li against models which predict substantial Li depletion in halo and old disk stars.

Key words: stars: abundances stars: Population II Galaxy: evolution cosmology: observations cosmic rays

* Based on observations collected at the European Southern Observatory, La Silla, Chile
** Tables 4 to 7 are available in electronic form only at the CDS via anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/abstract.html

Send offprint requests to: P. Molaro, Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste, Italy

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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