We review the advantages of using hot white dwarfs (WDs) as probes of the deuterium abundance in the local interstellar medium. We then discuss advantages of the Space Telescope Imaging Spectrograph (STIS) for such observations, as compared with earlier observations with the Goddard High Resolution Spectrograph (GHRS). The GHRS Ly α profile of the white dwarf HZ 43 is probably modified by the hot ‘hydrogen wall’ surrounding the Sun; but despite this complication, the sightline remains a promising one for an accurate determination of the deuterium abundance in the local interstellar medium.

We have computed synthetic spectra of the infrared B I transitions at 1.166 and 1.624 μm in order to examine the possibility of abundance determination by using these lines. We found that the IR boron lines are better observed in cool giants and supergiants. S/N > 150 and R ≈ 60000 are required in order to determine the boron abundances.

Lithium in cool magnetic CP stars in still poorly studied and estimations of the Li abundance in these stars are scarce. There is some evidence of variability of the LiI 6708 Â line, but this variability has not been studied systematicaly. Even the identification of the 6708 Â line with the LiI resonance doublet is still in doubt. This problem is important in the broader context of the Li abundance in various types of stars, as well as for deeper undersfanding of the magnetic star phonomenon itself. The reason for fhis is that the Li abundance in very sensitive to evolutionary status of the stars and their properties, such as the character and intensity of mixing processes.

We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. The unevolved stars in this sample present high (> 2.00) Li abundances. We found a few cases of subgiant stars which present high Li content. The Sun seems to be part of a population of nearly unevolved stars which have depleted their Li to a high degree: all other metal-normal, near ZAMS stars in our sample show higher than solar Li content. There seems to be no correlation of the degree of Li depletion with mass, atmospheric parameters or state of evolution: as an example we found a star (HR1532) almost identical to the Sun in its state of evolution and atmospheric parameters, but with over ten times the solar Li abundance. We propose that different histories of angular momentum distribution at star birth, and/or post-birth angular momentum evolution, may account for these differences.

Even though the existence of meridional currents in stars has been known for quite a long time (Eddington 1925, Vogt 1925), its exact structure as well as its influence on stellar evolution is still unclear. Some authors concentrated on finding the exact shape of meridional circulation in a rotating star, while others tried to model its effect on the chemical distribution in the interior. In all studies performed so far however, meridional circulation is considered in an asymptotic regime in which the advection of entropy by the meridional currents is supposed to balance exactly the source term of the non-zero radiative flux divergence. Other terms could however be added to that asymptotic regime which could turn out to dominate the transport of chemicals. We wish to present here preliminary results of 3D numerical simulation attempted to tackle this problem.

Late-type evolved stars are well known for the decrease with age of their rotation and lithium abundance. However, the root cause of this property as well as the relationship between rotation and lithium content in these stars are not yet completely established. In the present work, we study the link between rotation and lithium abundances in solar-type giant stars on the basis of a large sample of 380 stars of spectral type F, G and K.

We present the results of an analysis of seven faint K giants with strong Li lines, recently discovered during the Picodos Dias urvey, from high-resolution and high signal-to-noise-ratio spectra. The fundamental parameters of these stars, such as effective temperature, surface gravity, metallicity and microturbulence, were determined. We also obtained LTE abundances of Li and CNO elements and measured the 12C/13C ratios by spectral synthesis using the lines of Li I (λ6104Â and λ6708 Â), C2, CN, and [O I]. The studied Li K stars are found to be red giant branch stars with masses around 1M⊙.

Jehin et al. (1999) find that, in a sample of moderately metal-poor stars, a group is rich in s elements, and they propose an enrichment by accretion of matter by the winds of AGB stars. We tried to check the implications for the lithium abundances.

We determined the carbon and lithium abundances and carbon isotopic ratios for 4 peculiar carbon stars by means of spectral synthesis method. Li abundances were derived using Li resonance line at λ6707.8 Â. For carbon abundance determinations we used the lines of the red system of CN molecule. Spectral region of λλ7994 — 8030 Â containing the lines of molecules 12CN and 13CN was used also for 12C/13C ratio measuring. The high-resolution spectra were obtained on the 1.52m telescope of ESO with the Fiber-fed Extended Range Optical Spectrograph (FEROS). These observations were obtained under the agreement between the CNPq-Observatório Nacional, Brazil, and ESO.

We analyse the behavior of the projected rotational velocity vsin i for a sample of 20 lithium-rich evolved stars. Most of these stars show normal rotational velocity with respect to the typical lithium-normal evolved stars of the same spectral type. Stars presenting enhanced rotation show also high activity level. No sign of binarity was found for these lithium-rich evolved stars.

We analyze the Li depletion in the PTT-gap proposed by Martin (1997) using the young stars, with ages between 10 and 100 Myr, recently discovered by us during a survey around isolated T Tau stars.

We present lithium abundances for nine chromospherically young, kinematically old late-type stars. The data support the interpretation that these objects can be formed during the coalescence of a short-period binary.

We discuss estimates of stellar temperature, and the assemblage of a ‘critical set’ of target low-metallicity stars, from the HK Survey of Beers and collaborators, that can be used in the near future to put additional strong constraints on models for lithium production in the early Galaxy, and for inference of its primordial value.

We present the impact of meridional circulation and shear turbulence on the evolution of the lithium abundance at the surface of evolved stars originating from the hot side of the Li Dip. We show that our fully consistent treatment of the same hydrodynamical processes which can account for C and N anomalies in B type stars (Talon et al. 1997) and for the shape of the hot side of the Li dip in open clusters (Talon & Charbonnel 1998) also explains Li observations in stars with Teff higher than 7000K on the main sequence as well as in their evolved counterparts (see also Charbonnel & Talon 1999).

The role of nova outbursts in the galactic lithium production is still controversial. Photoionization model calculations of nova shells are presented in this contribution, aiming to identify the optimal post-outburst phase for detecting lithium emission lines from nova ejecta which may confirm its lithium enhancement. Predictions for the Li I λ6708 Â flux are made as a function of the envelope geometry, its physical parameters and properties of the central ionizing source.

It has been known for a long time (Mestel 1953) that the meridional circulation velocity in stars, in the presence of μ-gradients, is the sum of two terms, one due to the classical thermal imbalance (Ω-currents) and the other one due to the induced horizontal μ-gradients (μ-induced currents, or μ-currents in short). In the most general cases, μ-currents are opposite to Ω-currents. Vauclair (1999) has shown that such processes can, in specific cases, lead to a quasi-equilibrium stage in which both the circulation and the helium settling is frozen. Here we present computations of the circulation currents in halo star models, along the whole evolutionary sequences for four stellar masses with a metallicity of [Fe/H] = −2. We show that such a self-regulated process can account for the constancy of the lithium abundances and the small dispersion in the Spite plateau.

The predictions of Galactic chemical evolution models for D and 3He are described in connection with those on the other Galactic quantities for which observational constraints are available.

Models in agreement with the largest set of data predict deuterium depletions from the Big Bang to the present epoch smaller than a factor of 3 and do not allow for D/H primordial abundances larger than ∼ 4 × 10—5. Models predicting higher D consumption do not reproduce other observed features of our Galaxy.

If both the primordial D and 3He are low, models assuming that 90% of low-mass stars experience an extra-mixing during the red giant phase reproduce all the 3He observed abundances. The same percentage allows to fit also the observed carbon isotopic ratios, thus supporting the self-consistency of the extra-mixing mechanism.

The deuterium abundances in high-redshift QSO absorption-line systems could be an important constraint in models of galaxy formation. Here we investigate the role of galactic winds and massive cooling flows present during the formation of galaxies on the evolution of deuterium abundance. Destruction factors are calculated and the time and spatial scales for the dispersal through galactic winds of the processed deuterium-depleted gas are presented and related to the D/H determinations for QSO absorption-line systems. The calculations are derived from a chemodynamical model within a scenario in which the absorbers are located inside the hot halo of a young galaxy.

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.

Our understanding of the evolution of 4He and 7Li depends critically on the available data for these two elements at low metallicity. In particular, the degree to which there is a slope in an abundance vs metallicity regression can help determine the evolution of He, C, N, and O in dwarf galaxies in the case of 4He, and cosmic-ray induced nucleosynthesis of LiBeB in our own galaxy in the case of 7Li. Recent data and their implications will be discussed.