Recent observations of cool giants have shown that there exists a large range in their lithium abundances even for apparently similar stars. In order to explore whether this large spread could be interpreted in terms of mass, the Li I line at 6707.8 Å has been observed in more than 100 stars and these data have been combined with the already known lithium abundance data in literature. Absolute magnitudes of these stars have been estimated from the Hipparcos data and an attempt has been made to understand the Li evolution of a star as a function of its mass and the evolutionary status. There are strong evidences for extra-mixing taking place on the red giant branch which explain the unusually low abundances observed.

We present the results of a lithium study of the 220 Myr old cluster NGC 6475. Our data are merged with those from previous Li surveys of this cluster in order to construct a more statistically significant sample. The Li vs. effective temperature distribution of the merged sample is compared with the one of the co-eval, but more metal poor cluster M 34 and with the ones of the younger Pleiades and older Hyades. The results are discussed in the framework of non-standard Li depletion on the main-sequence between the age of the Pleiades (˜ 120 Myr) and that of the Hyades (˜ 600 Myr).

We report observations of lithium in a sample of 11 stars in the metal-poor open cluster NGC 2243, that were obtained from high-resolution spectroscopy at CASPEC (ESO 3.6m telescope). The targets are located at the turnoff region, plus one red giant star.

NGC 2243 is one of the most metal-poor open cluster, almost as deficient as 47 Tuc, but substantially younger (∼4 Gyrs and [Fe/H]=-0.5 dex), which makes it a very interesting case to compare with more metal rich coeval clusters on the one hand, and old metal-rich globular clusters (47 Tuc) on the other hand. The preliminary Lithium abundances obtained are discussed in this framework.

Lithium is a key element to establish the substellar nature of brown dwarf candidates. Theoretical calculations show that brown dwarfs with masses below ˜ 0.065 M⊙ preserve a significant fraction of their initial Li content while for higher masses total Li depletion occurs in short timescales. Lithium is preserved at masses well below the hydrogen burning mass. Strong lithium lines have been predicted and discovered in the spectra of brown dwarfs. Most of the bona fide brown dwarfs detected in stellar clusters and in the solar neighborhood have been confirmed to be substellar via detection of the lithium resonance doublet at 670.8 nm. I review these detections and the progress made in understanding the formation of Li lines in very cool high gravity dwarfs.

Lithium continues to be a surprising element and more than ever the study of its creation, destruction and distribution is giving us tools to understand, not only the chemical evolution of this element, but also the nature of mass loss of evolved giants and nucleosynthesis of other elements in cases of very low-metal giants. It also helps to set constraints for cosmological models. The presence of very strong lithium lines in some giant stars of different spectral types and stages of evolution has been considered up to the end of the nineties as a puzzle. To solve this problem, non standard evolutionary mechanisms must be invoked. We review here all the mechanisms presented in the literature and which are divided into internal and external processes of lithium enrichment. We will also discuss the observational tests which are being performed in order to discard (or not) some of them. In any case, the more realistic values of the lithium abundances in giants are, as we will see, the main test of these proposed scenarios. Because of this importance we discuss here the state of art of the Non-LTE determinations of lithium abundances in strong lithium giants. Evolved giants, with lithium abundances larger than that of the interstellar medium and with their important mass losses can be considered the most realistic sources of lithium in the Galaxy. We believe that a complete physical picture of this problem will give a powerful tool to understand the chemical evolution of a large part of all light elements.

In the Pico dos Dias Survey (PDS), devised to search for young stellar objects, we found also K giants presenting moderate to strong Lithium lines associated with IRAS sources. But there are some gK with weak or absent Li lines too. There is a dichotomy in the distribution of the IRAS spectral indices between both kinds of K stars. A model of an expanding shell with a mass-dependent velocity may explain this behavior, if the photospheric Li depletion takes only ˜2500 yrs.

We report here new results about a search for Li-rich stars among 52 G-K giant stars which are known to have near IR excess. Eleven giants have been found to have log ∊(Li) ≥ 1.0. Five are new Li-rich stars. We suspect circumstellar shells around one of them, HD 219025. There is no clear correlation between Li-richness and rotation, or with binarity.

We present Be abundances derived through spectral synthesis for two Li-rich giants and a Li-normal giant, plus α Cen A and B, based on observations of the Be II λ 3130.420 and 3131.066 Å lines obtained with the CASPEC spectrograph at the ESO 3.6m telescope.

The values derived for the two Li-rich giants (HD146850, HD787) agree with the one for the Li-normal giant (HD220321), and shows that Be was depleted in these stars (by > 90% i.e. by a factor of 10 or larger from the initial Pop I value (logN(Be)= 1.4)).

This result implies that the original Li in these stars was almost completely destroyed, and that Li is most probably produced in red giants.

We are conducting a survey on the 7Li/6Li ratio in interstellar space in order to seek limits on the variation in this ratio. The analysis is based on the technique we adopted in extracting the 11B/10B ratio. This technique uses a line of comparable strength, from a species likely to occupy the same volume of the interstellar cloud, as a template for separating velocity components within the line profile. For our study of the 7Li/6Li ratio, the K I line at 4044 Å serves as the velocity template. Our initial focus is on the variation in the 7Li/6Li ratio around the star-forming region IC 348. Our high-resolution observations of the Li I lines toward o and ζ Per show remarkably different isotope ratios: 7Li/6Li = 2-4 and 11, respectively, where the Solar System ratio is 12.3 and cosmic ray spallation yields a ratio of about 2. The significance of the very low ratio toward o Per is that it is essentially the value predicted for cosmic rays through spallation reactions. The direction to o Per passes closer to IC 348, a site of massive star formation, than does the line of sight to ζ Per. Furthermore, our analysis of OH column densities (Federman, Weber, & Lambert 1996) showed that the cosmic ray flux through o Per's diffuse clouds is higher than average, presumably reflecting the nearby presence of IC 348.

We discuss the primordial nucleosynthesis in lepton asymmetric Universe models. In order to better estimate the universal baryon-mass density parameter ωb, we try to remove the uncertainty from the theoretical prediction of primordial 7Li abundance. We propose a new method to determine the primordial 7Li by the use of isotopic abundance ratio 7Li/6Li in the interstellar medium which exhibits the minimum effects of the stellar processes.

We present lithium abundances for ∼50 late-type members of the ∼30 — 50 Myr old open clusters IC 2602 and IC 2391 derived from high-resolution spectra obtained at ESO and CTIO. These data enlarge and extend to cooler temperatures previous Li surveys of these clusters by Stauffer et al. (1989) and Randich et al. (1997). We discuss the lithium vs. temperature distribution in the two clusters and we compare our results with those obtained for the Pleiades (∼120 Myr). The results are discussed in the general framework of lithium depletion in young clusters, from the pre-main sequence to the age of the Pleiades.

Five giants and 11 subgiants of the metal-poor globular cluster NGC 6397 are analysed. In this Poster we present the lithium abundances derived. The present Li abundances and those of turnoff stars by Pasquini & Molaro (1996) are complementary in terms of stellar evolution stage, and show the Li abundances decreasing off the main sequence along the red giant branch.

We present a determination of the lithium abundance from high quality spectra in an extremely metal poor star where the lithium line had not been detected.

The 7Li enrichment - mass loss scenario has been constructed using the strong connection found between solar metallicity Li-rich giants and IRAS sources. We show here that the Li-rich metal poor first-ascent red giants are not IRAS sources, although they are loosing Li enriched matter in form of gas.

The analysis of 72 binaries with component of luminosity class III shows that the behavior of Li abundance in such systems follows the same pattern presented by their single counterparts. Binarity seems to affect the lithium dilution in systems presenting orbital period lower than about 100 days.

Lithium abundances, determined for 120 subgiant stars in Lèbre et al. (1999), are analyzed and compared with predictions for dilution. To this purpose, the evolutionary status of the sample as well as the individual masses have been determined. We look for the distributions of A(Li) and Vsini with mass when those stars evolve along the subgiant branch. Our results bring a new light on the Lithium and rotation discontinuities in evolved phases.

We present new high resolution spectroscopic data of the 6707.81 Å Li I line for 117 G and K Bright Giants (class of luminosity II). We derived Lithium abundances that we analysed along the stellar parameters: Teff, M* and Vsini. With the CORAVEL spectrometers (at Observatoire de Haute Provence [OHP] and at European Southern Observatory [ESO]), De Medeiros & Mayor (2000) obtained radial velocities and Vsini with an uncertainty of about 0.3 kms—1 and 2.0 kms—1, respectively. CORAVEL data also provide indication on the binary nature of our sample stars (32% are binary stars).

We selected a sample of active cool stars detected in the EUV band by the ROSAT WFC and performed spectroscopic and photometric observations. We inferred spectral type, luminosity class, distance, binary status, rotational velocity. Here we show the results of the Li abundances determination from the Li I 6707.8 Å spectral line.

We have a list of nearby bulge-like turnoff stars with metallicities in the range −0.3 ≤ [Fe/H] ≤ +0.6, for which we have the absolute magnitude from Hipparcos, Geneva photometry (therefore temperature and metallicity), and radial velocity from Coravel (Grenon 1990, 1997). From Hipparcos data, the turnoff of these field stars indicate an age of 10-11 Gyr, which would be the age of the most metal-rich component of the bulge.

We obtained high resolution échelle spectra with FEROS, with the aim to carry out detailed analysis of these stars. In this paper we present the Li abundance for 40 of these metal-rich and old dwarf stars, as a function of their temperatures.

A full abundance analysis have been carried out in 12 galactic J-stars. The analysis shows: a) 12C/13C ratios are low, b) the abundance of s-process and rare-earth elements with respect to the stellar metallicity is nearly-solar, [< heavy > /Fe] = 0.10 ± 0.11 c) Tc is not present in most of the stars although upper limits are placed in WZ Cas and WX Cyg, probably two SC-type stars, and d) all the stars are Li-rich, log ∈(Li)> 1. The location of J-stars in an empirical H-R diagram when compared with that of the normal N-type carbon stars, suggests that J-stars may be in the early-AGB phase. The different mechanism proposed to be responsible of this Li production are briefly discussed.