Paola Sestito

Evolution of lithium beyond the solar age: A Li survey of the old open cluster NGC 188

We have determined Li abundances for 11 G-type stars in the 6-8 Gyr old open cluster NGC 188. These data significantly enlarge the number of cluster stars with Li measurements, allowing us to extend the investigation of Li depletion in open clusters to ages well beyond the age of the Sun. We have also inferred the cluster metallicity which turns out to be solar. We find that solar-type stars in NGC 188 are only slightly more Li depleted than the much younger Hyades and no more Li depleted than stars of similar temperature in the 2-4 Gyr younger cluster M 67. At variance with M 67, NGC 188 members show virtually no scatter in their Li abundances. Surprisingly, no solar-type star in NGC 188 appears as Li depleted as the Sun or as the most Li depleted stars in M 67. We discuss the implications of these results for mechanisms of internal mixing and Li depletion in main sequence stars.

Lithium evolution in intermediate age and old open clusters: NGC 752 revisited

We present new high resolution spectroscopic observations of the intermediate age (~2 Gyr) open cluster NGC 752. We investigate the Li vs. T eff distribution and we obtain a new accurate determination of the cluster metallicity. We compare the results for NGC 752 with other intermediate age and old clusters spanning the age range from the Hyades (~0.6 Gyr) to NGC 188 (~6–8 Gyr). We find that NGC 752 has a solar iron content ([ Fe/H

The evolution of lithium depletion in young open clusters: NGC 6475 -

]=+0.01\pm0.04

Multi-Object Spectroscopy of Open Clusters with FLAMES: Preliminary GTO Results

), at variance with early reports of sub-solar metallicity. We find that NGC 752 is only slightly more Li depleted than the younger Hyades and has a Li pattern almost identical to that observed in the ~2 Gyr old IC 4651 and NGC 3680. As for the latter clusters, we find that NGC 752 is characterized by a tight Li vs. T eff distribution for solar-type stars, with no evidence for a Li spread as large as the one observed in the solar age solar metallicity M 67. We discuss these results in the framework of mixing mechanisms and Li depletion on the main sequence (MS). We conclude that the development of a large scatter in Li abundances in old open clusters might be an exception rather than the rule (additional observations of old clusters are required), and that metallicity variations of the order of ~ ± 0.2 dex do not affect Li depletion after the age of the Hyades.

Lithium abundances in intermediate age and old clusters

We have carried out a high resolution spectroscopic survey of the 220–250 Myr old cluster NGC 6475: our main purpose is to investigate Li evolution during the early stages of the Main Sequence. We have determined Li abundances for 33 late F to K–type X–ray selected cluster candidates, extending the samples already available in the literature; for part of the stars we obtained radial and rotational velocities, allowing us to confirm the membership and to check for binarity. We also estimated the cluster metallicity which turned out to be over–solar (

Abundances of giants in four Galactic clusters (Sestito+, 2008)

{\rm [Fe/H]}\rm =+0.14 \pm 0.06

Abundances of giants in five Galactic clusters (Bragaglia+, 2008)

). Our Li analysis evidenced that (i) late F–type stars ( T eff

Old open clusters as key tracers of Galactic chemical evolution. II. Iron and elemental abundances i

\ga

Element abundances of 7 stars of NGC 6253 (Sestito+, 2007)

6000 K) undergo a very small amount of Li depletion during the early phases on the ZAMS; (ii) G–type stars (6000

Lithium and Metallicity in the Intermediate Age Open Cluster NGC 752

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