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Astron. Astrophys. 356, L25-L29 (2000)

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Letter to the Editor

Evolution of lithium in solar-type stars: clues from intermediate age clusters *

S. Randich 1, L. Pasquini 2 and R. Pallavicini 3

1 Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy (randich@arcetri.astro.it)
2 European Southern Observatory, Karl-Schwartzschild-Strasse 2, 85748, Garching bei München, Germany
3 Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

Received 12 January 2000 / Accepted 2 March 2000


We present Li abundances for 14 solar-type stars in the intermediate age ([FORMULA] Gyr) clusters IC 4651 and NGC 3680. The [FORMULA] n(Li) vs. effective temperature distributions are compared with those of the similar age cluster NGC 752, of the younger Hyades (600 Myr) and of the older M 67 (4.5 Gyr) and NGC 188 (6-7 Gyr) clusters. Neither IC 4651 nor NGC 3680 show the dispersion in Li which is observed in M 67. The 2 Gyr clusters have very similar Li vs. [FORMULA] distributions; in addition, stars in the upper envelope of the M 67 distribution have the same Li content as stars in the 2 Gyr clusters, suggesting that either they have not suffered any significant depletion between [FORMULA] 2 and 4.5 Gyr or they had a much slower Li depletion. Mechanisms that lead to Li depletion on the main sequence are discussed in the light of these observations. None of the existing models seem to reproduce well the observed features.

Key words: Galaxy: open clusters and associations: individual: NGC 3680 – Galaxy: open clusters and associations: individual: IC 4651 – stars: abundances – stars: interiors

* Based on observations carried out at the European Southern Observatory, La Silla, Chile

Send offprint requests to: S. Randich

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© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000