1,098 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&
Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate
We investigate the effects of the atomic interaction in the Superradiant
Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned
laser beam. We show that for a homogeneous atomic sample the atomic interaction
has only a dispersive effect, whereas in the inhomogeneous case it may increase
the decay of the matter-wave grating.Comment: 12 pages, 4 figures, presented to the XII International Laser Physics
Workshop, August 24-29, Hamburg, to be published in Laser Physic
Survey and Assessment of Laws on the Informal Sector
This study classifies the laws affecting the informal sector and assesses the extent of the empowerment of the sector based on the provisions in the laws that allow for organization, decision making mechanisms and transfer of power from the traditional center to another. Results indicate that, to some extent, four groups within the sector are accorded empowerment through Philippine laws: the agricultural sector, small and medium enterprises, industrial home workers and cooperatives. These groups are allowed to form organizations and to participate in decision making bodies. Decision making is accorded to certain groups among informal sector, which, in some cases, comprise the majority members in decision making bodies. Nowhere among the laws is a shift of power provided from the traditional or government decision makers to the informal sector. However, certain groups within the IS have participated in the institution of some policies and the realization of programs for their own advantage.informal financial sectors, small and medium enterprises
Survey and Assessment of Laws on the Informal Sector
This study classifies the laws affecting the informal sector and assesses the extent of the empowerment of the sector based on the provisions in the laws that allow for organization, decision making mechanisms and transfer of power from the traditional center to another. Results indicate that, to some extent, four groups within the sector are accorded empowerment through Philippine laws: the agricultural sector, small and medium enterprises, industrial home workers and cooperatives. These groups are allowed to form organizations and to participate in decision making bodies. Decision making is accorded to certain groups among informal sector, which, in some cases, comprise the majority members in decision making bodies. Nowhere among the laws is a shift of power provided from the traditional or government decision makers to the informal sector. However, certain groups within the IS have participated in the institution of some policies and the realization of programs for their own advantage.informal financial sectors, small and medium enterprises
Non-LTE abundances of Mg and K in extremely metal-poor stars and the evolution of [O/Mg], [Na/Mg], [Al/Mg] and [K/Mg] in the Milky Way
LTE abundances of light elements in extremely metal-poor (EMP) stars have
been previously derived from high quality spectra. New derivations, free from
the NLTE effects, will better constrain the models of the Galactic chemical
evolution and the yields of the very first supernovae. The NLTE profiles of the
magnesium and potassium lines have been computed in a sample of 53 extremely
metal-poor stars with a modified version of the program MULTI and adjusted to
the observed lines in order to derive the abundances of these elements. The
NLTE corrections for magnesium and potassium are in good agreement with the
works found in the literature. The abundances are slightly changed, reaching a
better precision: the scatter around the mean of the abundance ratios has
decreased. Magnesium may be used with confidence as reference element. Together
with previously determined NLTE abundances of sodium and aluminum, the new
ratios are displayed, for comparison, along the theoretical trends proposed by
some models of the chemical evolution of the Galaxy, using different models of
supernovae
Up-frequency conversion in a two-resonant-wave high-gain free-electron-laser amplifier
A free-electron laser is able to resonate at two different frequencies, both in free space and in a waveguide. The two waves have positive and negative slippage. We describe the nonlinear interaction between the two waves by a set of partial differential equations which in free space do not require the slowly varying envelope approximation (SVEA). In a waveguide a less restrictive SVEA is applied to each wave. By injecting a small signal at the low frequency, a strong signal and bunching are produced at the high frequency. This effect suggests a new method of generating short wavelength radiation
Lead abundance in the uranium star CS 31082-001
In a previous paper we were able to measure the abundance of uranium and
thorium in the very-metal poor halo giant BPS CS 31082-001, but only obtained
an upper limit for the abundance of lead (Pb). We have got from ESO 17 hours of
additional exposure on this star in order to secure a detection of the minimum
amount of lead expected to be present in CS 31082-001, the amount arising from
the decay of the original content of Th and U in the star. We report here this
successful detection. We find an LTE abundance log(Pb/H)+12=-0.55 \pm 0.15 dex,
one dex below the upper limits given by other authors for the similar stars CS
22892-052 and BD +17d3248, also enhanced in r-process elements. From the
observed present abundances of Th and U in the star, the expected amount of Pb
produced by the decay of 232Th, and 238U alone, over 12-15 Gyr is -0.73\pm 0.17
dex. The decay of 235U is more difficult to estimate, but is probably slightly
below the contribution of 238U, making the contribution of the 3 actinides only
slightly below, or even equal to, the measured abundance. The contribution from
the decay of 234U has was not included, for lack of published data. In this
sense our determination is a lower limit to the contribution of actinides to
lead production. We comment this result, and we note that if a NLTE analysis,
not yet possible, doubles our observed abundance, the decay of the 3 actinides
will still represent 50 per cent of the total lead, a proportion higher than
the values considered so far in the literature.Comment: 4 pages, LateX, A&A Letters Accepte
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