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Astron. Astrophys. 325, 535-541

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Lithium in M 67: evidence for spread in a solar age cluster*

L. Pasquini1, S. Randich2, and R. Pallavicini3

1European Southern Observatory, Casilla 19001, Santiago 19, Chile
2European Southern Observatory, Karl Schwarzschild Str. 2, D-87546 Garching, Germany
3Osservatorio Astronomico di Palermo, Palazzo dei Normanni, I-90134 Palermo, Italy

Received 22 January 1997 / Accepted 24 March 1997


We present high resolution observations of main sequence stars in the solar age, solar metallicity open cluster M 67. For the first time we show conclusively that a spread in lithium abundances exists among solar-type stars belonging to this cluster. This implies that standard models with only convection as a mixing mechanism can hardly account for the spread at each colour, and that the Li abundance is not a good age indicator for solar-type stars. The comparison of Li abundances in M 67 (age FORMULA yrs) with those in the younger Hyades cluster ( FORMULA yrs) shows that the less depleted stars in M 67 have a Li content only ~ 0.25 dex below similar stars in the Hyades. Considering the ~ 4 Gyrs difference between the two clusters, this indicates that standard lithium destruction mechanisms are very inefficient (if present at all) in many solar-type stars during most of their main sequence lifetime. On the other hand, almost 40% of our sample stars show a significant Li depletion, with values comparable to the Sun. Our sample also includes one SB2 binary, for which a very high Li abundance was previously reported. We found an abundance significantly higher than in single stars, but our spectra are inconsistent with those previously published.

Key words: stars: abundances - open clusters: individual: M 67

*Based on observations collected at ESO, La Silla

Send offprint requests to: Luca Pasquini

© European Southern Observatory (ESO) 1997

Online publication: September 9, 1997
Last change: April 28, 1998