102 research outputs found
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&
Liaudies gerovės tyrimo metodologiniai pagrindai
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?
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?
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
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 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,
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
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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