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It is widely accepted that binary interactions are responsible for the shaping of planetary nebula. However, these binary interactions and evolutionary channels are poorly understood. Our recent study revealed a newly discovered population of low-luminosity, low-metallicity, likely binaries in the Magellanic Clouds: dusty post-RGB stars. They are likely to have evolved off the RGB via binary interaction. In this paper we present preliminary results of the first radial velocity monitoring of the post-RGB stars in the Small Magellanic Cloud (SMC) and the implications on stellar (binary) evolution. We also investigate their link, if any, to the planetary nebulae systems.

We present near-infrared spectro-interferometric studies of red supergiant (RSG) stars using the VLTI/AMBER instrument, which are compared to previously obtained similar observations of AGB stars. Our observations indicate spatially extended atmospheric molecular layers of water vapor and CO, similar as previously observed for Mira stars. Data of VY~CMa indicate that the molecular layers are asymmetric, possibly clumpy. Thanks to the spectro-interferometric capabilities of the VLTI/AMBER instrument, we can isolate continuum bandpasses, estimate fundamental parameters of our sources, locate them in the HR diagram, and compare their positions to recent evolutionary tracks. For the example of VY CMa, this puts it close to evolutionary tracks of initial mass 25-32 M⊙. Comparisons of our data to hydrostatic model atmospheres, 3d simulations of convection, and 1d dynamic model atmospheres based on self-excited pulsation models indicate that none of these models can presently explain the observed atmospheric extensions for RSGs. The mechanism that levitates the atmospheres of red supergiant is thus a currently unsolved problem.

The detected variety in chemistry and circumstellar shell morphology of the limited sample of Galactic post-AGB stars is so large, that there is no consensus yet on how individual objects are linked by evolutionary channels. The evaluation is complicated by the fact that the distances and hence luminosities of these objects are poorly known. In this contribution we report on our project to overcome this problem by focusing on a significant sample of post-AGB stars with known distances: those in the LMC. Via cross-correlation of the infrared SAGE-SPITZER catalogue with optical catalogues we selected a sample of 322 LMC post-AGB candidates based on their position in the various colour-colour diagrams. We determined the fundamental properties of 82 of them, using low resolution optical spectra that we obtained at Siding Spring and SAAO. We selected a subsample to be studied at high spectral resolution in order to obtain accurate abundances of a wide range of species. This will allow us to connect the theoretical predictions with the obtained surface chemistry at a given luminosity and metallicity. By this, we want to constrain important structure parameters of the evolutionary models. Preliminary results of the selection process are presented.

We have obtained infrared spectra of carbon-rich AGB stars in three nearby galaxies – the Large and Small Magellanic Clouds, and the Fornax dwarf spheroidal galaxy. Our primary aim is to investigate gas compositions and mass-loss rate of these stars as a function of metallicity, by comparing AGB stars in several galaxies with different metallicities. C2H2are detectable from AGB stars, and possibly PAHs are subsequently formed from C2H2. Thus, it is worth investigating chemical processes at low metallicity. These stars were observed using the Infrared Spectrometer (irs) onboard theSpitzer Space Telescopewhich covers 5–35 μm region, and the Infrared Spectrometer And Array Camera (isaac) on the Very Large Telescope which covers the 2.9–4.1 μm region. HCN, CH and C2H2molecular bands, as well as SiC and MgS dust features are identified in the spectra. The equivalent width of C2H2molecular bands is larger at lower metallicity, thus PAHs might be abundant in AGB stars at low metallicity. We find no evidence that mass-loss rates depend on metallicity. Chemistry of carbon stars is affected by carbon production during the AGB phase rather than the metallicities. We argue that lower detection rate of PAHs from the interstellar medium of lower metal galaxies is caused by destruction of PAHs in the ISM by stronger UV radiation field.

We report on recent progress in the modelling of the near-IR spectra of young stellar populations, i.e. populations in which red supergiants (RSGs) are dominant. First, we discuss the determination of fundamental parameters of RSGs using fits to their near-IR spectra with new PHOENIX model spectra; RSG-specific surface abundances are accounted for and effects of the microturbulence parameter are explored. New population synthesis predictions are then described and, as an example, it is shown that the spectra of young star clusters in M82 can be reproduced very well from 0.5 to 2.4 micrometers. We warn of remaining uncertainties in cluster ages., Proceedings of IAU Symp. 241 on Stellar Populations as Building Blocks of Galaxies, ed. A. Vazdekis et al. (2007). 4 pages, 6 postscript figures, uses iaus.cls.

The international Project "Lithium in magnetic CP stars" has been put into op- eration using telescopes of the Crimean Astrophysical Observatory (2.6-m reflector ZTSH), European Southern Observatory (1.4-m CAT and 1.52-m with FEROS), Mount Stromlo Ob- servatory (74-inch), Nordic Optical Telescope Scientific Association (2.4-m with SOFIN), and Special Astrophysical Observatory of the Russian Academy of Sciences (6-m BTA). Here we present an historical report of the different scientific results of this project since its beginning in 1996.