22,364 research outputs found
Anomalous globular clusters: insights from neutron capture elements abundances
Thanks to the large amount of spectroscopic and photometric data assembled in
the last couple of decades, the assumption that all globular clusters (GCs)
contain a simple mono-metallic stellar population has been modified. Besides
the common variations in the elements created/destroyed in the H-burning
processes, spreads and/or multi-modalities in heavier elements have been
detected in a few objects. Among the most remarkable chemical inhomogeneity in
these anomalous objects is the internal variation in the neutron-capture
(n-capture) elements, that can provide some information about the material from
which stars were born. I report a summary of the chemical pattern observed in
GCs where variations in n-capture have been detected, and the connection
between these chemical features and the distribution of stars along the
color-magnitude diagrams in the context of the lively debate on multiple
stellar populations.Comment: 5 pages, 4 fugures, proceedings of the meeting "Reading the book of
globular clusters with the lens of stellar evolution", Rome, Nov. 26-28,
2012, to be published in Memorie della Societa' Astronomica Italian
Chemical composition of stellar populations in Omega Centauri
We derive abundances of Fe, Na, O, and s-elements from GIRAFFE@VLT spectra
for more than 200 red giant stars in the Milky Way satellite Omega Centauri.
Our preliminary results are that: (i) we confirm that Omega Centauri exibiths
large star-to-star metallicity variations ( 1.4 dex); (ii) the
metallicity distribution reveals the presence of at least five stellar
populations with different [Fe/H]; (iii) a clear Na-O anticorrelation is
clearly observed for the metal-poor and metal-intermediate populations while
apparently the anticorrelation disappears for the most metal-rich populations.
Interestingly the Na level grows with iron.Comment: 2 pages, 2 figures. To appear in the proceedings of IAU Symp. 268
"Light elements in the Universe" (C. Charbonnel, M. Tosi, F. Primas, C.
Chiappini, eds., Cambridge Univ. Press
Recovery of fluctuation spectrum evolution from tomographic shear spectra
Forthcoming large angle surveys are planned to obtain high precision
tomographic shear data. In principle, they will allow us to recover the spectra
of matter density fluctuation, at various redshift, through the inversion of
the expressions yielding shear from fluctuation spectra. This was discussed in
previous work, where SVD techniques for matrix inversion were also shown to be
the optimal tool to this aim. Here we show the significant improvements
obtainable by using a 7 bin tomography, as allowed by future Euclid data, as
well as the question of error propagation from shear to fluctuation spectra. We
find that the technique is a promising tool, namely for the analysis of baryon
physics throug high-l shear spectra and to test the consistency between
expansion rate and fluctuation growth.Comment: 22 pages, 10 figure
Charge and Magnetic Flux Correlations in Chern-Simons Theory with Fermions
Charge and magnetic flux bearing operators are introduced in Chern-Simons
theory both in its pure form and when it is coupled to fermions. The magnetic
flux creation operator turns out to be the Wilson line. The euclidean
correlation functions of these operators are shown to be local and are
evaluated exactly in the pure case and through an expansion in the inverse
fermion mass whenever these are present. Physical states only occur in the
presence of fermions and consist of composite charge-magnetic flux carrying
states which are in general anyonic. The large distance behavior of the
correlation functions indicates the condensation of charge and magnetic flux.Comment: Latex, 17 page
Singular quasilinear elliptic systems in
The existence of positive weak solutions to a singular quasilinear elliptic
system in the whole space is established via suitable a priori estimates and
Schauder's fixed point theorem
Thermal and non-thermal signatures of the Unruh effect in Casimir-Polder forces
We show that Casimir-Polder forces between two relativistic uniformly
accelerated atoms exhibit a transition from the short distance thermal-like
behavior predicted by the Unruh effect, to a long distance non-thermal
behavior, associated with the breakdown of a local inertial description of the
system. This phenomenology extends the Unruh thermal response detected by a
single accelerated observer to an accelerated spatially extended system of two
particles, and we identify the characteristic length scale for this crossover
with the inverse of the proper acceleration of the two atoms. Our results are
derived separating at fourth order in perturbation theory the contributions of
vacuum fluctuations and radiation reaction field to the Casimir-Polder
interaction between two atoms moving in two generic stationary trajectories
separated by a constant distance, and linearly coupled to a scalar field. The
field can be assumed in its vacuum state or at finite temperature, resulting in
a general method for the computation of Casimir-Polder forces in stationary
regimes.Comment: 6 pages, 1 figure. Revised versio
Horizontal-branch morphology and multiple stellar populations in the anomalous globular cluster M22
M22 is an anomalous globular cluster that hosts two groups of stars with
different metallicity and s-element abundance. The star-to-star light-element
variations in both groups, with the presence of individual Na-O and C-N
anticorrelations, demonstrates that this Milky-Way satellite has experienced a
complex star-formation history. We have analysed FLAMES/UVES spectra for seven
stars covering a small color interval, on the reddest horizontal-branch (HB)
portion of this cluster and investigated possible relations between the
chemical composition of a star and its location along the HB. Our chemical
abundance analysis takes into account effects introduced by deviations from the
local-thermodynamic equilibrium (NLTE effects), that are significant for the
measured spectral lines in the atmospheric parameters range spanned by our
stars. We find that all the analysed stars are barium-poor and sodium-poor,
thus supporting the idea that the position of a star along the HB is strictly
related to the chemical composition, and that the HB-morphology is influenced
by the presence of different stellar populations.Comment: 21 pages, 3 figures, accepted for publication in Ap
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