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Astron. Astrophys. 345, 249-255 (1999)


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Beryllium abundance in lithium-rich giants *

B.V. Castilho 1, F. Spite 2, B. Barbuy 1, M. Spite 2, J.R. De Medeiros 3 and J. Gregorio-Hetem 1

1 Universidade de São Paulo, CP 3386, São Paulo, SP, 01060-970, Brazil
2 Observatoire de Paris-Meudon, DASGAL, URA 335 CNRS, F-92195 Meudon Cedex, France
3 Universidade Federal do Rio Grande do Norte, Natal, RN, 59072-970, Brazil

Received 26 November 1998 / Accepted 2 February 1999

Abstract

About 2[FORMULA] of the Population I red giants show lithium abundances significantly larger than expected by dilution due to mixing by classical convection and, in some of them, the lithium abundance reaches values similar to (and even larger than) the Pop I value (meteoritic, open clusters etc.) around logN(Li) = 3.3. The classical convection predicts also a (smaller) dilution of beryllium and (an even smaller one) of boron.

Two main interpretations of the Li-rich giants are possible:

  • the initial Li has been somehow preserved (perhaps by the inhibition of the classical mixing)

  • on the contrary, a mixing, deeper than the classical one, took place in some (or all?) giants, leading to a dilution of the superficial lithium but sometimes overcompensating for it by an internal production of lithium, with transport to the surface (by the Cameron-Fowler mechanism).

In the first interpretation, Be (more robust than Li) is a fortiori preserved, in the second one, a mixing deeper than the classical one should dilute Be more than the classical Be dilution.

We have observed the Be II [FORMULA] 3130.420 and 3131.066 Å lines in two Li-rich giants and three reference stars: one Li-poor giant and [FORMULA] Cen A and B. The observations were carried out at the ESO 3.6m telescope using the CASPEC spectrograph. By comparing the observed spectra with spectrum synthesis calculations we show that for the three giant stars the Be abundance is low, suggesting that, in these giants, Be is very depleted ([FORMULA]90[FORMULA]) from the initial Pop I value (logN(Be)[FORMULA]1.4). This result implies that the original Li in these stars must have been almost completely destroyed, and that the high Li abundances in the Li-rich red giants is most probably due to Li production in these stars.

Key words: nuclear reactions, nucleosynthesis, abundances – stars: abundances – stars: late-type

* Observations collected at the European Southern Observatory - ESO, Chile

Send offprint requests to: B.V. Castilho

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999

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