Galactic globular cluster 47 Tucanae: new ties between the chemical and dynamical evolution of globular clusters?

It is generally accepted today that Galactic globular clusters (GGCs) consist of at least two generations of stars that are different in their chemical composition and perhaps age. However, knowledge about the kinematical properties of these stellar generations, which may provide important information for constraining evolutionary scenarios of the GGCs, is still limited. We therefore study the connections between chemical and kinematical properties of different stellar generations in the Galactic globular cluster 47 Tuc. To achieve this goal, we used abundances of Li, O, and Na determined in 101 main sequence turn-off (TO) stars with the aid of 3D hydrodynamical model atmospheres and NLTE abundance analysis methodology. We divided our sample TO stars into three groups according to their position in the [Li/Na]-[Na/O] plane to study their spatial distribution and kinematical properties. We find that there are statistically significant radial dependencies of lithium and oxygen abundances, A(Li) and A(O), as well as that of [Li/Na] abundance ratio. Our results show that first-generation stars are less centrally concentrated and dynamically hotter than stars belonging to subsequent generations. We also find a significant correlation between the velocity dispersion and O and Na abundance, and between the velocity dispersion and the [Na/O] abundance ratio.Comment: 4 pages, 6 figures, accepted for publication in A&

ISO observations of the planetary nebula Lindsay 305 in the Small Magellanic Cloud

We present ISO (Infrared Space Observatory) observations of the planetary nebula Lindsay 305 (L 305) in the Small Magellanic Cloud. L 305 is very prominent in the ISOCAM frames at 6.75 and 11.5 $\mu$m, although it is under the detection limit at 4.5 $\mu$m. The obtained spectral energy distribution shows a strong mid-IR excess, which, depending on the amount of energy radiated at wavelengths longer than 11.5 $\mu$m, may be as large as $\sim 1500 L_{\odot}$. However, since an accurate estimate of the total nebular luminosity is not available up to date, the evolutionary status of L 305 can not yet be constrained precisely.Comment: 4 pages, 2 figures, to appear in the Publications of the Astronomical Society of Japa

Beyond the Galaxy with Gaia: evolutionary histories of galaxies in the Local Group

Gaia will play an important role in providing information about star formation histories, merging events, intergalactic streams etc., for nearby galaxies of the Local Group. One of the most crucial contributions will be proper motions, especially for stars in the outermost parts of the galaxies, obtainable for stellar populations to ~150 kpc with RGB stars. Together with radial velocities for the brightest giants <80 kpc, this will provide membership information for individual stars and global kinematical picture of the most nearby galaxies, including the Magellanic Clouds (MCs). Gaia will also provide photometric metallicities (\sigma([M/H])<0.3) for individual giants and/or supergiants in dwarf galaxies to ~200 kpc. MSTO ages will be possible for the youngest stellar populations in the most nearby galaxies (e.g., MCs), whereas stars on RGB/AGB may provide age estimates for populations to ~150 kpc. Gaia will allow to study the outermost parts of the galaxies, which (because of their large spatial extent) are difficult to assess from the ground. Apart from allowing to clarify the structure and evolution of the dwarf galaxies, this will also make it possible to investigate galactic tidal debris, thus providing additional details for the global picture of formation and evolution of the Milky Way Galaxy.Comment: Proceedings of "The Three Dimensional Universe With Gaia", Paris, October 4-7, 2004, 4 pages, 3 figure

AGB Stars as Tracers of Star Formation Histories: Implications for GAIA Photometry and Spectroscopy

We argue that tracing star formation histories with ESA's space mission GAIA using main sequence turn-off (MSTO) point dating will mainly be effective in cases of mild interstellar extinction (E(B-V)<0.5). For higher reddenings the MSTO approach will be severely limited both in terms of traceable ages (t<0.5 Gyr at 8 kpc; E(B-V)=1.0) and/or distances (d<2 kpc for t=15 Gyr; E(B-V)=1.0), since the MSTO will be located at magnitudes too faint for GAIA. AGB stars may alternatively provide precise population ages with GAIA for a wide range of ages and metallicities, with traceable distances of up to 250 kpc at E(B-V)=0 (d=15 kpc if E(B-V)=2.0). It is essential however that effective temperatures precise to 0.01 dex, metallicities to 0.2 dex, and E(B-V) to 0.03 are derived for individual stars, in order to obtain their ages precise to 0.2 dex. This task is quite challenging for GAIA photometry and spectroscopy, though preliminary tests show that comparable precisions may be achieved with GAIA medium band photometry.Comment: Proceedings of the Monte Rosa Conference "GAIA spectroscopy, science and technology" Gressoney Saint Jean (Valle d'Aosta, Italy), Sept 9-12, 2002, ed. U. Munari, ASP Conf. Ser., in pres

Broad-band photometric colors and effective temperature calibrations for late-type giants. II. Z<0.02

(Abridged) We investigate the effects of metallicity on the broad-band photometric colors of late-type giants, and make a comparison of synthetic colors with observed photometric properties of late-type giants over a wide range of effective temperatures (T_eff=3500-4800 K) and gravities (log g=0.0-2.5), at [M/H]=-1.0 and -2.0. The influence of metallicity on the synthetic photometric colors is generally small at effective temperatures above \~3800 K, but the effects grow larger at lower T_eff, due to the changing efficiency of molecule formation which reduces molecular opacities at lower [M/H]. To make a detailed comparison of the synthetic and observed photometric colors of late type giants in the T_eff--color and color--color planes, we derive a set of new T_eff--log g--color relations based on synthetic photometric colors, at [M/H]=-0.5, -1.0, -1.5, and -2.0. While differences between the new T_eff--color relations and those available from the literature are typically well within ~100 K, effective temperatures predicted by the scales based on synthetic colors tend to be slightly higher than those resulting from the T_eff--color relations based on observations, with the offsets up to ~100 K. This is clearly seen both at [M/H]=-1.0 and -2.0, especially in the T_eff--(B-V) and T_eff--(V-K) planes. The consistency between T_eff--log g--color scales based on synthetic colors calculated with different stellar atmosphere codes is very good, with typical differences being well within \Delta T_eff~70 K at [M/H]=-1.0 and \Delta T_eff~40 K at [M/H]=-2.0.Comment: 20 pages, 11 figures, A&A accepte

Photometric colors of late-type giants: theory versus observations

To assess the current status in the theoretical modeling of the spectral properties of late-type giants, we provide a comparison of synthetic photometric colors of late-type giants (calculated with PHOENIX, MARCS and ATLAS model atmospheres) with observations, at [M/H]=0.0 and -2.0. Overall, there is a good agreement between observed and synthetic colors, and synthetic colors and published Teff-color relations, both at [M/H]=0.0 and -2.0. Deviations from the observed trends in Teff-color planes are generally within \pm 150K (or less) in the effective temperature range Teff=3500-4800K. Synthetic colors calculated with different stellar atmosphere models typically agree to ~100K, within a large range of effective temperatures and gravities. Some discrepancies are seen in the Teff-(B-V) plane below Teff~3800K at [M/H]=0.0, due to difficulties in reproducing the 'turn-off' to the bluer colors which is seen in the observed data at Teff~3600K. Note that at [M/H]=-2.0 effective temperatures given by the scale of Alonso et al. (1999) are generally lower than those resulting from other Teff-color relations based both on observed and synthetic colors.Comment: 2 pages, 1 figure. Proceedings of the IAU Symposium 232 "The Scientific Requirements for Extremely Large Telescopes", eds. P. Whitelock, B. Leibundgut, and M. Dennefel