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A short overview is presented of current issues concerning the production and evolution of Li, Be and B in the Milky Way. It is argued that the currently popular idea that Galactic Cosmic rays are accelerated inside metal-rich superbubbles (which leads “naturally” to the production of primary Be and B, as observed) encounters the same problems as the previously popular idea of supernovae accelerating their own ejecta. A major challenge to theories of light element production is presented by the recent (and still preliminary) data suggesting a surprisingly high and ~constant abundance of Li in halo stars; attempts to explain such a “plateau” are critically examined.

Although the data for the Milky Way are not yet conclusive about the existence of a N/O abundance gradient along the Galactic disk, such a gradient is clearly seen in other spiral galaxies [7]. In this work we computed the abundance gradient of N/O for the MW. In our formalist the MW formed out of two-infall episodes, one forming the halo/thick disk on a short timescale and a second one forming the thin disk on a much longer timescale. Moreover, in our framework the thin disk formed inside-out (see details in [3]). Here we show that a negative gradient is predicted for N/O once we adopt stellar yields where rotation is taken into account (see Fig.1 - thick line). We point out that although [5] did not include formally the hot bottom burning (HBB), models computed with their stellar yields are still compatible with the available observational data.

NGC 6822 is an isolated irregular galaxy of the Local Group located at 495 kpc from our Galaxy and at 880 kpc from M31, there are no small galaxies in its neighbourhood, and it does not show tidal effects.

We describe some models for the chemical evolution of dwarf spheroidals of the Local Group: Draco, Sagittarius, Sculptor, Sextan, Ursa Minor and Carina. These models assume one long or at maximum two episodes of star formation followed by a strong galactic wind. The efficiency of the star formation is lower than in the Milky Way and the star formation histories take into account the information derived from the observed color-magnitude diagrams of these galaxies. Under these hypotheses, we are able to well reproduce the observed [α/Fe] ratios in these galaxies and to predict their age-metallicity relations and stellar metallicity distributions.

After reviewing some general properties of late-type dwarf galaxies, we present and discuss chemical evolution models for two windy starburst dwarfs: NGC 1569 and NGC1705. Both have their recent star formation history and stellar initial mass function derived from color-magnitude diagram analysis. In order to reproduce the available observations, we must take into account the presence of dark matter halos and the development of late galactic winds. Two possible solutions are envisaged which might explain the origin of the different N/O ratios observed in NGC1569 and NGC1705: either () small variations in the stellar initial mass spectrum, leading to the production of different amounts of nitrogen and oxygen from intermediate- and highmass stars; or () the complex interplay among the mechanisms determining cooling and heating of the gas and its conversion into stars. Although the second is by far the most effective in determining the global properties of these galaxies, it still remains also the most elusive.

It has been recently shown in Chiappini et al. [2] that models of chemical evolution computed with the Meynet & Maeder [4] yields for the whole range of masses, predict a slower increase of N with respect to what is obtained with other sets of stellar yields, thus leading to important implications for the interpretation of the DLAs abundance data. Thanks to the slower increase of N in time, the DLAs abundance patterns can be reproduced by “bursting models” and in this framework, the “low N/O” (≃ −2.2 dex) and “high N/O” (≃ −1.6 dex) groups of DLAs could be explained as systems which show differences in their star formation histories rather than an age difference (see [2] references therein). In fact, we were able to obtain models that show both a low log(N/O) and a [O/Fe]∼0.2-0.3 dex during almost all their evolution, in agreement to what is observed in some DLAs. Alternative interpretations (see [2] for a discussion) of the “low N/O” DLAs suggested in the literature imply a high overabundance of α-elements in disagreement with observations. DLAs could also be identified with outer regions of spiral galaxies but in this case DLAs with low log(N/O) would be quite young systems (younger than ∼150 Myr) and no discontinuity in the log(N/O) vs. log(O/H) diagram would be expected [2].

We have studied the effects of an hypothetical initial generation made only of very massive stars ( > 100, pair-creation SNe) on the chemical and photometric evolution of spheroidal systems. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results produced are at variance with the main observational constraints of ellipticals such as the average [< α/ >✲] ratio in stars and the color-magnitude diagram.

New results of the Primordial Helium abundance () measurement by radio recombination line (RRL) observations from five galactic HII regions are presented. The RRL observations were carried out with two telescopes: RT32 (22.4 and 8.3 GHz, Medicina, Italy) and RT22 (36.5 and 22.4 GHz, Pushchino, Russia). The results of the first run of the low frequency RRL observations (408 MHz) with the Croce del Nord radiotelescope (Medicina Observatory, Italy) are also presented.

This poster illustrates the results of ongoing simulations – within our previously developed modeling framework – allowing for stochastic accretion within closed and open systems. All models include three “zones” (halo, thick disk, and thin disk) and are initialized with only the halo, the abundances for which are assumed to be primordial. The time history of star formation is computed directly from the model equations rather than being assumed without instantaneous recycling [1]. The yields and deterministic rates are the same as used in our previous work [2]. f stoc

Spectacular advances in the volume, the precision, and the accuracy of chemical abundance data for stars in many environments are now being delivered. Corresponding kinematic data are starting to appear, while the essential distances and calibrations await GAIA, still a decade away. Quantitative galaxy models with high spatial resolution are being developed. How do we use these data and models? Applications to calibrate the input functions to chemical evolution models are underway, such as supernova and AGB yields. The more basic question, what are the dominant processes in Galaxy formation and evolution, remains as a challenge: our goal is to identify the failings of the models, and make progress. Many specific areas of potential progress are now clear, ranging from the true age and abundance distribution in the Galactic Bulge, through the origin of the old thick disk, to the accretion history of the outer halo. Since the technology is new, most effort is still being devoted to the observationally easiest questions: all questions require massive surveys to address them. Many such surveys are underway: progress will be rapid, if well-focussed.