2,084 research outputs found
Capture of field stars by globular clusters in dense bulge regions
The recent detection of a double Red Giant Branch in the optical
color-magnitude diagram (CMD) of the bulge globular cluster HP1 (Ortolani et
al. 1997), a more populated metal-poor steep one corresponding to the cluster
itself, and another metal-rich curved, led us to explore in the present Letter
the possibility of capture of field stars by a globular cluster orbiting in
dense bulge regions over several gigayears. Analytical arguments, as well as
N-body calculations for a cluster model of 10^5 solar masses in a bulge-like
environment, suggest that a significant fraction of cluster stars may consist
of captures. Metal-poor globular clusters in the inner bulge, like HP1,
contrasting at least in Delta [Fe/H] = 1.0 dex with respect to the surrounding
metal-rich stars, are ideal probes to further test the capture scenario. In
turn, if this scenario is confirmed, the double RGB of HP1 could provide direct
estimates of blanketing amounts, which is fundamental for the photometric
calibration of metal-rich stellar populations.Comment: 6 pages, 2 included figures, aas2pp4,sty Latex style. To be published
in Astrophysical Journal Letter
HST NICMOS Photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4
We present results from NICMOS Hubble Space Telescope observations of the
reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan
4, obtained through the filters F110W and F160W (nearly equivalent to J and H).
For the first time the turnoff region of Liller 1 and the main sequence of
Terzan 5 and Terzan 4 are reached, as well as the horizontal branch of UKS 1.
The magnitude difference between the turnoff and the red horizontal branch
is used as an age indicator. From
comparisons with new isochrones in the NICMOS photometric system, we conclude
that the two metal-rich clusters NGC 6528 and Terzan 5 are coeval within
uncertainties () with 47 Tucanae. Liller 1 and UKS 1 are confirmed as
metal-rich globular clusters. Terzan 4 is confirmed as an interesting case of a
metal-poor cluster in the bulge with a blue horizontal branch.Comment: 7 pages, 6 figures, accepted for publication in A&
Homogeneous and inhomogeneous magnetic phases of constrained dipolar bosons
We study the emergence of several magnetic phases in dipolar bosonic gases
subject to three-body loss mechanism employing numerical simulations based on
the density matrix renormalization group(DMRG) algorithm. After mapping the
original Hamiltonian in spin language, we find a strong parallelism between the
bosonic theory and the spin-1 Heisenberg model with single ion anisotropy and
long-range interactions. A rich phase diagram, including ferromagnetic,
antiferromagnetic and non-local ordered phases, emerges in the half-filled
one-dimensional case, and is preserved even in presence of a trapping
potential.Comment: v2: 9 pages, 15 figures, extended version, new numerical calculations
on the BKT transition, accepted for pubblication in PR
Italian networking of public experimental sites working on Organic Farming: an experience of networking in research
Research in organic farming, especially with an agro-ecological approach, is strictly linked to local conditions and interactions among several variables. The paper will present an example of a process developed in the Italian context to integrate and harmonize research in organic farming from different research stations, with different local conditions. Collecting similar and comparable data from different research stations participating in the network can have an interesting impact in results of organic farming experiments, due to high number and variability of data. ARSIA Toscana, with the aim of creating an Italian National Network of public experimental stations working in organic farming, involved FIRAB as a facilitator of the participatory process. The proposed process follows two parallel paths: individual questionnaire to single experimental sites to know the specific activities in place on organic farming and a series of meetings with direct involvement and exchange among researchers and policy makers from different regions to comment results of the questionnaire and future development of organic research in public experimental stations. The main outcome of the process has been the choice of a specific transversal topic to build the network: the development of synthetic agro-environmental indicators
DMRG Simulation of the SU(3) AFM Heisenberg Model
We analyze the antiferromagnetic Heisenberg chain by means of
the Density Matrix Renormalization Group (DMRG). The results confirm that the
model is critical and the computation of its central charge and the scaling
dimensions of the first excited states show that the underlying low energy
conformal field theory is the Wess-Zumino-Novikov-Witten
model.Comment: corrections and improvements adde
Magnetic properties of commensurate Bose-Bose mixtures in one-dimensional optical lattices
We investigate magnetic properties of strongly interacting bosonic mixtures
confined in one dimensional geometries, focusing on recently realized Rb-K
gases with tunable interspecies interactions. By combining analytical
perturbation theory results with density-matrix-renormalization group
calculations, we provide quantitative estimates of the ground state phase
diagram as a function of the relevant microscopic quantities, identifying the
more favorable experimental regimes in order to access the various magnetic
phases. Finally, we qualitatively discuss the observability of such phases in
realistic setups when finite temperature effects have to be considered.Comment: 9 pages, 7 figures, to be published in EPJ ST special issue on "Novel
Quantum Phases and Mesoscopic Physics in Quantum Gases
On critical phases in anisotropic spin-1 chains
Quantum spin-1 chains may develop massless phases in presence of Ising-like
and single-ion anisotropies. We have studied c=1 critical phases by means of
both analytical techniques, including a mapping of the lattice Hamiltonian onto
an O(2) nonlinear sigma model, and a multi-target DMRG algorithm which allows
for accurate calculation of excited states. We find excellent quantitative
agreement with the theoretical predictions and conclude that a pure Gaussian
model, without any orbifold construction, describes correctly the low-energy
physics of these critical phases. This combined analysis indicates that the
multicritical point at large single-ion anisotropy does not belong to the same
universality class as the Takhtajan-Babujian Hamiltonian as claimed in the
past. A link between string-order correlation functions and twisting vertex
operators, along the c=1 line that ends at this point, is also suggested.Comment: 9 pages, 3 figures, svjour format, submitted to Eur. Phys. J.
El Roque de Los Muchachos Site Characteristics. III. Analysis of Atmospheric Dust and Aerosol Extinction
Canary Islands are normally interested by dominant North-East winds that, in
some meteorological conditions, can transport sand at high altitude from the
Sahara desert. The dust may affect the efficiency of the telescopes and
decreases the transparency of the sky. In order to maximize the scientific
return of the telescopes located at the ORM, we present an analysis of the
atmospheric dust content and its effects on astronomical observations. B, V and
I dust aerosol astronomical extinction are derived. Using a 5 years series
database of data taken from the four channel TNG dust monitor, we compute a
mean hourly and daily values of the dust content. We have detected particles
having size 0.3, 0.5, 1.0 and 5.0 um. Using a power law we have derived the
content of 10.0 um particles. We found a typical local dust concentration
ranging from 3x10^6 particles per cubic meter at 0.3 um, to 10^3 at 5.0 um and
10 at 10.0 um, increasing up to 3 order of magnitudes during the dust storms,
with a relative higher increase of 1.0, 5.0 and 10.0 um particles. The number
of local dust storm events is the same in winter- and summertime, but, the
average background and storm-related increases in the dust concentration in
summer are significantly higher than in winter. In a uniform approximation,
during the dust storms, an average height of the dust layer of 2.5 km above the
telescope is inferred. During the sand storms La Palma Island is affected by an
almost uniform layer extending up to 5 km above the sea level, down, at least
the height of the telescope. The visible extinction is dominated by particles
at 1.0, 5.0 and 10.0 um. In agreement with the results from Carlsberg Automatic
Meridian Circle (CAMC) we find a typical extinction during dust storms of about
0.2 mag/airmass.Comment: Accepted for publication in A&A. 9 pages, 11 figures. This work is
the continuation of a series of papers concerning a detailed study of the
Astroclimatology at ORM. The two previous papers (both Lombardi et al.) have
reference PASP.2006.118.1198-1204 and PASP.2007.119.292-30
Reflectivity measurements in uniaxial superconductors: a methodological discussion applied to the case of La(2-x)Sr(x)CuO(4)
Most of the novel superconductors are uniaxial crystals, with metallic planes
() orthogonal to an insulating axis (). Far-infrared measurements of the
reflectivity provide valuable information on their low-energy
electrodynamics, but involve delicate experimental issues. Two of them are a
possible contamination of from the c axis and the
extrapolation of the data to =0, both above and below .
Here we discuss quantitatively these issues with particular regard to
LaSrCuO, one of the most studied high- materials.Comment: 13 pages with 3 Fig
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