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Aims. The aim of this work is to shed some light on the problem of the formation of carbon stars of R-type from a detailed study of their chemical composition.

Aims.We present new results of our ongoing chemical study of carbon stars in Local Group galaxies to test the critical dependence of s-process nucleosynthesis on the stellar metallicity.

Context.Abundance analysis of post-AGB objects as probes of AGB nucleosynthesis.

We present high resolution optical spectroscopic observations of IRAS 09425-6040, a peculiar, extremely red, C-rich AGB star showing prominent O-rich dust features in its ISO infrared spectrum attributed to crystalline silicates. Our analysis shows that IRAS 09425-6040 is indeed a C-rich star slightly enriched in lithium (${\log ({\rm Li/H}) + 12} \sim 0.7$) with a low 12C/13C = $15 \pm 6$ratio. We also found some evidence that it may be enriched in s-elements. Combining our results with other observational data taken from the literature we conclude that the star is possibly an intermediate-mass TP-AGB star ($M \ga 3~M_\odot$) close to the end of its AGB evolution which may have only very recently experienced a radical change in its chemistry, turning into a carbon-rich AGB star.

We present the first results of our ongoing chemical study of carbon stars in the Local Group of galaxies. We used spectra obtained with UVES at the 8.2 m Kueyen-VLT telescope and a new grid of spherical model atmospheres for cool carbon-rich stars which include polyatomic opacities, to perform a full chemical analysis of one carbon star, BMB-B 30, in the Small Magellanic Cloud (SMC) and two, IGI95-C1 and IGI95-C3, in the Sagittarius Dwarf Spheroidal (Sgr dSph) galaxy. Our main goal is to test the dependence on the stellar metallicity of the s-process nucleosynthesis and mixing mechanism occurring in AGB stars. For these three stars, we find important s-element enhancements with respect to the mean metallicity ([M/H]), namely $\rm [s/M]\approx+1.0$, similar to the figure found in galactic AGB stars of similar metallicity. The abundance ratios derived between elements belonging to the first and second s-process abundance peaks, corresponding to nuclei with a magic number of neutrons $N=50$(88Sr, 89Y, 90Zr) and $N=82$(138Ba, 139La, 140Ce, 141Pr), agree remarkably well with the theoretical predictions of low mass $(M <3~M_\odot)$metal-poor AGB nucleosynthesis models where the main source of neutrons is the 13C$(\alpha,n)^{16}$O reaction activated during the long interpulse phase, in a small pocket located within the He-rich intershell. The derived C/O and 12C/13C ratios are, however, more difficult to reconcile with theoretical expectations. Possible explanations, like the extrinsic origin of the composition of these carbon stars or the operation of a non-standard mixing process during the AGB phase (such as the cool bottom process), are discussed on the basis of the collected observational constraints.

We present a spectroscopic study of D461, a giant star belonging to Draco dwarf spheroidal galaxy. From spectral synthesis in LTE we derive a lithium abundance of $\rm log$ϵ(Li) = $3.5\pm0.4$and a C/O ratio between 3 and 5. This is the first detection of a lithium rich C-star in a dwarf spheroidal galaxy. Basing on stellar models of appropriate chemical composition, we show that a similar C enrichment is compatible with that expected for a low mass low metallicity thermally pulsing AGB star, undergoing few third dredge up episodes. The position in the $\log~g$–$\log~T_{\rm{eff}}$diagram of D461 is also compatible with this theoretical scenario. In particular, the low effective temperature, lower than that expected for a low metallicity giant star, is a consequence of the huge increase of the envelope opacity occurring after the carbon dredge up. The Li enrichment may be explained if a deep circulation would take place during the interpulse period, the so called cool bottom process. In spite of the low resolution of our spectra, we derive a lower limit for the carbon isotopic ratio, namely 12C/$^{13}\rm C>40$, and a constraint for the Ba abundance, namely $\rm 0.5<[Ba/Fe]< 2$. The proposed scenario also fits these further constraints. Then, we estimate that the mass of D461 ranges between 1.2 and 2 $M_\odot$, which corresponds to an age ranging between 1 and 3 Gyr. We conclude that this star is more massive and younger than the typical stellar population of Draco.

The IRAIT (International Robotic Antarctic Infrared Telescope) project (Tosti et al. , 2006, Proc. 6267-29 V. 2) is based on a 80 cm aperture telescope to observe in the infrared range. It is due to start operations in spring 2008, several months after installation in Dome C (Antarctica). We present the contributions made to such project by the Institute for Space Studies of Catalonia (IEEC) and the University of Granada, whose participation is mainly focused in developing the moving optical system for the secondary (M2) and tertiary (M3) mirrors of the telescope. Moving parts of the optical system provide focusing and chopping capabilities, implemented in M2, and a rotation mechanism, implemented in M3, allow observation in either Nasmyth foci. The work package includes the design and construction of both mirrors, the mechanical supports, the electronics and the control software, all prepared to work at the low temperatures at Antarctica. A Spanish company, NTE, was contracted to carry out the design and manufacture. Tests at low temperature and integration in the telescope have been done during summer 2006.

Recent advances in the determination of stellar abundances and their impact on the study of nucleosynthesis and the chemical evolution of galaxies are discussed. It is argued that detailed interpretation of the abundance patterns among chemical elements found at different metallicities still requires solid spectroscopic data. Despite current improvements in abundance analyses, these are not, however, free from systematic errors which can hide the real history of the chemical evolution. Some examples are discussed.

Recent advances in the determination of stellar abundances and their impact on the study of nucleosynthesis and the chemical evolution of galaxies are discussed. It is argued that detailed interpretation of the abundance patterns among chemical elements found at different metallicities still requires solid spectroscopic data. Despite current improvements in abundance analyses, these are not, however, free from systematic errors which can hide the real history of the chemical evolution. Some examples are discussed.?

AMICA (Antarctic Multiband Infrared CAmera) is an instrument designed to perform astronomical imaging in the near- (1-5??m) and mid- (5?27 ?m) infrared wavelength regions. Equipped with two detectors, an InSb 2562and a Si:As 1282IBC, cooled at 35 and 7 K respectively, it will be the first instrument to investigate the potential of the Italian-French base Concordia for IR astronomy. The main technical challenge is represented by the extreme conditions of Dome C (T ?-90 ?C, p ?640 mbar). An environmental control system ensures the correct start-up, shut-down and housekeeping of the various components of the camera. AMICA will be mounted on the IRAIT telescope and will perform survey-mode observations in the Southern sky. The first task is to provide important site-quality data. Substantial contributions to the solution of fundamental astrophysical quests, such as those related to late phases of stellar evolution and to star formation processes, are also expected.

The IRAIT (International Robotic Antarctic Infrared Telescope) project (Tosti et al. , 2006, Proc. 6267-29 V. 2) is based on a 80 cm aperture telescope to observe in the infrared range. It is due to start operations in spring 2008, several months after installation in Dome C (Antarctica). We present the contributions made to such project by the Institute for Space Studies of Catalonia (IEEC) and the University of Granada, whose participation is mainly focused in developing the moving optical system for the secondary (M2) and tertiary (M3) mirrors of the telescope. Moving parts of the optical system provide focusing and chopping capabilities, implemented in M2, and a rotation mechanism, implemented in M3, allow observation in either Nasmyth foci. The work package includes the design and construction of both mirrors, the mechanical supports, the electronics and the control software, all prepared to work at the low temperatures at Antarctica. A Spanish company, NTE, was contracted to carry out the design and manufacture. Tests at low temperature and integration in the telescope have been done during summer 2006.?

The Concordia Station (Candidi 2003), on the Antarctica Plateau, will soon become one of the best observatories to perform infrared observations in the 2–20 μm atmospheric windows and beyond, thanks to its low sky background, low temperature and high atmospheric transparency. The possibility of passively cooling the telescope is a further advantage. We describe here the first permanent Antarctic infrared telescope, under development for the Dome C base. It is the International Robotic Antarctic Infrared Telescope (IRAIT). We briefly outline a few scientific motivations for it, then we review the technical characteristics and the status of its development. The infrared camera for IRAIT is described in another dedicated paper in this volume.

AbstractRecent advances in the knowledge of the evolutionary status of asymptotic giant branch (AGB) stars and of the nucleosynthesis processes occurring in them are discussed, and used to interpret abundance determinations for s-process elements, lithium and CNO isotopes in several types of AGB stars. We focus our attention mainly on carbon-rich AGB stars. By combining these different constraints we conclude that most carbon stars in the solar neighborhood are of low mass (M=3 M?), their abundances being a consequence of the operation of thermal pulses and the third dredge-up. However, the observed abundances in carbon stars of the R and J types cannot be explained by this standard scenario. These stars may not be on the AGB, but possibly in the core-He burning phases; their envelopes may have been polluted with nuclear ashes of the core-He flash, followed by CNO re-processing enhancing 13C. Observational evidence suggesting the operation of non-standard mixing mechanisms during the AGB phase is also discussed.

Abundances of lithium, heavy elements, and carbon isotope ratios have been measured in 12 J-type Galactic carbon stars. The abundance analysis shows that in these stars the abundances of s-process elements with respect to the metallicity are nearly normal. Tc is not present in most of them, although upper limits have been derived for WZ Cas and WX Cyg, perhaps two SC-type rather than J-type carbon stars. The Rb abundances, obtained from the resonance ?7800 Rb Iline, are surprisingly low, probably owing to strong non-LTE effects in the formation of this line in cool carbon-rich stars. Lithium and 13C are found to be enhanced in all the stars. These results together with the nitrogen abundances and oxygen isotope ratios measured by Lambert et al. and Harris et al. are used to discuss the origin of J stars. The luminosity and variability class of the stars studied would indicate that they are low-mass (M2-3 M?), less evolved objects than the normal carbon stars, although the presence of some luminous (Mbol< -5.5) J stars in our Galaxy (WZ Cas may be an example) and in other galaxies, suggests the existence of at least two types of J stars, with different formation scenarios depending upon the initial mass of the parent star. Standard evolutionary AGB models are difficult to reconcile with all the observed chemical characteristics. In fact, they suggest the existence of an extra mixing mechanism that transports material from the convective envelope down to hotter regions where some nuclear burning occurs. This mechanism would act preferably on the early-AGB phase in low-mass stars. Mixing at the He-core flash and the binary system hypothesis are also discussed as alternatives to the above scenario.

A sample of recent type Ia supernovae has been observed from La Palma. Spectra of there supernovae were taken at two different phases: around maximum and between one and two months after maximum. We present here our observations and discuss the existence of intrinsic differences within the sample.

We present observations of the ?3130 Å Beii resonance doublet in stars of intermediate metal deficiency, -0.6=[Fe/H]=-1.1 obtained with the Intermediate Dispersion Spectrograph and IPCS detector at the 2.5 m Isaac Newton Telescope on La Palma. The derived beryllium abundances range from 5.6×10-12 (one hafl solar) to 2×10-12 (one sixth solar). These values, interpolated between the sets of previous beryllium measurements at higher and at lower metallicities, serve to confirm the monotonic variation of the Be abundance with Fe during the evolution of the galactic disc. We find that there was no extreme burst of Be production in the halo. To circumvent the effects of depletion, a statistical set of data is needed, for which the upper envelope can be used to trace galactic Be evolution. We note that no observations with sufficient sensitivity to detect Be in the extremely metal deficient stars of the halo have been reported to date.

The new observational [O/Fe] vs [Fe/H] relationship in halo dwarfs is analyzed in terms of a model of chemical evolution for the solar neighbourhood. The role of nucleosynthesis prescriptions for SN II and SN I (both Ia and Ib) is analyzed. We show that by adopting iron yields for SN II according to the observations of SN 1987A and by assuming double degenerate systems to be the progenitors of SN Ia and Wolf-Rayet stars to be the progenitors of SN Ib, it is possible to reproduce quite well the behaviour of the [O/Fe] ratio for halo and disk stars. Nevertheless, best agreement is obtained when introducing in addition a variable IMF during the halo evolution.

Intermediate resolution (?/d? ~ 25 000) CCD spectra of the oxygen triplet at ?7770 Å have been analyzed to determine oxygen abundances in a sample of metal-deficient stars with metallicities covering the range -2.5=[Fe/H]=-0.2. Important oxygen overabundances ([O/Fe]=1) are found in the more metal deficient stars of the sample. We briefly discuss the information that these observations provide about the early nucleosynthesis history and chemical evolution of the Galaxy.

Different stellar sources may have contributed to the 7Li enrichmentof the Galaxy: type-II supernovae, novae, and AGB stars. In the latter case, the interplay between the Hot Bottom Burning (HBB) process (via the Cameron-Fowler mechanism) and a very high mass-loss rate before the evolution off the AGB (the so-called ‘superwind’ phase), can lead to a significant production of 7Li from low- and intermediate-mass AGB stars (Travaglio et al., 2001). We have now undertaken an observational campaign aimed at constraining our stellar and Galactic models, with a twofold goal: (i) to assemble a compilation of high-resolution spectra of Galactic, unevolved (i.e. dwarfs), warm(spectral type F) stars, in a selected metallicity range (-1.0 ≤>[Fe/H] ≤ -0.3), using the ESO 1.5m telescope and the FEROS spectrograph; (ii) to carry out a Li survey among a sample of selected AGB stars, to investigate the possible correlation between7Li abundance (when detected) and mass-loss rate.

Context.Binary systems experiencing one or two common envelope episodes during the red giant branch or the Hertzsprung gap phases can produce a single star, evolving along the Hayashi track, as a final outcome. Even if these objects are expected to be very common in nature, a proper description of their evolution and physical properties is still missing. Moreover, this scenario (red giant merging scenario) has been invoked as the progenitor systems of early-R stars, by assuming that the physical conditions developed as a consequence of the cores merging could produce the mixing into the convective envelope of fresh carbon that was synthesized during the He-flash.

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