102 research outputs found

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

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    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&

    Liaudies gerovės tyrimo metodologiniai pagrindai

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    The aim of the article is to reveal methodological principles of politico-economic investigation of people’s welfare. The requirements for the investigation of theoretical problems of people’s welfare are disclosed with reference to the classics of Marxism-Leninism. It is shown how the current concepts of people’s welfare correspond to the discovered methodological requirements.Straipsnyje analizuojami liaudies gerovės politinio ekonominio tyrimo metodologiniai pagrindai. Remiantis marksizmo-leninizmo teorija formuluojami metodologiniai reikalavimai liaudies gerovės teoriniams tyrimams: jie turi užtikrinti sisteminio principo taikymą. Išskiriamos skirtingos liaudies gerovės sampratos. Viena jų liaudies gerovę laiko asmeninių poreikių patenkinimo rezultatu. Antroji samprata liaudies gerove laiko gyventojų apsirūpinimą būtinomis pragyvenimui materialinėmis ir dvasinėmis gėrybėmis arba visomis gyvenimo sąlygomis. Trečioji samprata gerove supranta žmonių veiklos rezultatą, pačią veiklą. Autorius visas šias sampratas laiko nepakankamomis ir siūlo koncepciją, kuri liaudies gerovę apibrėžia kaip naudingumo realizavimo rezultatą. Naudingumu čia suprantamas pozityvus, per veiklą pasireiškiantis objektyvių gyvenimo sąlygų savybių ir žmogaus racionalių poreikių sistemos santykis. Teigiama, kad siūlomoje koncepcijoje geriau negu kitose pagrindžiami ir išvystomi liaudies gerovės genezės klausimai. Ši koncepcija atitinka iškeltus metodologinius analizės reikalavimus ir gali padėti efektyviau spręsti liaudies gerovės kėlimo problemas

    Can we trust elemental abundances derived in late-type giants with the classical 1D stellar atmosphere models?

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    We compare the abundances of various chemical species as derived with 3D hydrodynamical and classical 1D stellar atmosphere codes in a late-type giant characterized by T_eff=3640K, log g = 1.0, [M/H] = 0.0. For this particular set of atmospheric parameters the 3D-1D abundance differences are generally small for neutral atoms and molecules but they may reach up to 0.3-0.4 dex in case of ions. The 3D-1D differences generally become increasingly more negative at higher excitation potentials and are typically largest in the optical wavelength range. Their sign can be both positive and negative, and depends on the excitation potential and wavelength of a given spectral line. While our results obtained with this particular late-type giant model suggest that 1D stellar atmosphere models may be safe to use with neutral atoms and molecules, care should be taken if they are exploited with ions.Comment: Poster presented at the IAU Symposium 265 "Chemical Abundances in the Universe: Connecting First Stars to Planets", Rio de Janeiro, 10-14 August 2009; 2 pages, 1 figur

    Abundance of zirconium in the globular cluster 47 Tuc: a possible Zr-Na correlation?

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    We determined abundances of Na and Zr in the atmospheres of 237 RGB stars in Galactic globular cluster (GGC) 47 Tuc (NGC 104), with a primary objective of investigating possible differences between the abundances of Zr in the first generation (1P) and second generation (2P) stars. For the abundance analysis, we used archival UVES/GIRAFFE spectra obtained during three different observing programmes. Abundances were determined from two Na I and three Zr I lines, using 1D hydrostatic ATLAS model atmospheres. The target stars for the abundance analysis were limited to those with 4200 \leq TeffT_{\rm eff} \leq 4800 K. This is the largest sample of GGC stars in which Na and Zr abundances have been studied so far. While our mean [Na/Fe] and [Zr/Fe] ratios agree well with those determined in the earlier studies, we find a weak but statistically significant correlation in the [Zr/Fe][Na/Fe]{\rm [Zr/Fe]} - {\rm [Na/Fe]} plane. A comparison of the mean [Zr/Fe] abundance ratios in the 1P and 2P stars suggests a small but statistically significant Zr over-abundance in the 2P stars, Δ[Zr/Fe]2P1P+0.06\Delta {\rm [Zr/Fe]}_{\rm 2P-1P}\approx+0.06 dex. Also, our analysis shows that stars enriched in both Zr and Na are more centrally concentrated. However, we find no correlation between their distance from the cluster centre and their full spatial velocity. While there may be some influence of CN line blends on the determined Zr abundances, it seems very unlikely that the detected Zr-Na correlation, for the slightly higher Zr abundances in the 2P stars, would be caused by the CN blending alone. The obtained results indicate that, in 47 Tuc, some amount of Zr should have been synthesised by the same polluters that enriched 2P stars with the light elements. Unfortunately, our data alone do not allow us to distinguish which of the two scenarios, or whether or not a combination of both, could have operated in this GGC

    Granulation signatures in the spectrum of the very metal-poor red giant HD122563

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    A very high resolution (R=200,000), high signal-to-noise ratio (S/N=340) blue-green spectrum of the very metal-poor ([Fe/H]=-2.6) red giant star HD122563 has been obtained by us at McDonald Observatory. We measure the asymmetries and core wavelengths of a set of unblended FeI lines covering a wide range of line strength. Line bisectors exhibit the characteristic C-shape signature of surface convection (granulation) and they span from about 100 m/s in the strongest FeI features to 800 m/s in the weakest ones. Core wavelength shifts range from about -100 to -900 m/s, depending on line strength. In general, larger blueshifts are observed in weaker lines, but there is increasing scatter with increasing residual flux. Assuming local thermodynamic equilibrium (LTE), we synthesize the same set of spectral lines using a state-of-the-art three-dimensional hydrodynamic simulation for a stellar atmosphere of fundamental parameters similar to those of HD122563. We find good agreement between model predictions and observations. This allows us to infer an absolute zero-point for the line shifts and radial velocity. Moreover, it indicates that the structure and dynamics of the simulation are realistic, thus providing support to previous claims of large 3D-LTE corrections, based on the hydrodynamic model used here, to elemental abundances and fundamental parameters of very metal-poor red giant stars obtained with standard 1D-LTE spectroscopic analyses.Comment: ApJL, in pres
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