4,460 research outputs found
The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs)
is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this
data-base to perform an homogeneous systematic analysis of the evolved
sequences (namely, Red Giant Branch (RGB), Horizontal Branch (HB) and
Asymptotic Giant Branch (AGB)). Based on this analysis, we present: (1) a new
procedure to measure the level of the ZAHB (V_ZAHB) and an homogeneous set of
distance moduli obtained adopting the HB as standard candle; (2) an independent
estimate for RGB metallicity indicators and new calibrations of these
parameters in terms of both spectroscopic ([Fe/H]_CG97) and global metallicity
([M/H], including also the alpha-elements enhancement). The set of equations
presented can be used to simultaneously derive a photometric estimate of the
metal abundance and the reddening from the morphology and the location of the
RGB in the (V,B-V)-CMD. (3) the location of the RGB-Bump (in 47 GGCs) and the
AGB-Bump (in 9 GGCs). The dependence of these features on the metallicity is
discussed. We find that by using the latest theoretical models and the new
metallicity scales the earlier discrepancy between theory and observations
(~0.4 mag) completely disappears.Comment: 51 pages, 23 figures, AAS Latex, macro rtrpp4.sty included, accepted
by A
Gauge invariance of parametrized systems and path integral quantization
Gauge invariance of systems whose Hamilton-Jacobi equation is separable is
improved by adding surface terms to the action fuctional. The general form of
these terms is given for some complete solutions of the Hamilton-Jacobi
equation. The procedure is applied to the relativistic particle and toy
universes, which are quantized by imposing canonical gauge conditions in the
path integral; in the case of empty models, we first quantize the parametrized
system called ``ideal clock'', and then we examine the possibility of obtaining
the amplitude for the minisuperspaces by matching them with the ideal clock.
The relation existing between the geometrical properties of the constraint
surface and the variables identifying the quantum states in the path integral
is discussed.Comment: 23 page
The surprising external upturn of the Blue Straggler radial distribution in M55
By combining high-resolution HST and wide-field ground based observations, in
ultraviolet and optical bands, we study the Blue Straggler Star (BSS)
population of the low density galactic globular cluster M55 (NGC 6809) over its
entire radial extent. The BSS projected radial distribution is found to be
bimodal, with a central peak, a broad minimum at intermediate radii, and an
upturn at large radii. Similar bimodal distributions have been found in other
globular clusters (M3, 47 Tucanae, NGC 6752, M5), but the external upturn in
M55 is the largest found to date. This might indicate a large fraction of
primordial binaries in the outer regions of M55, which seems somehow in
contrast with the relatively low (\sim 10%) binary fraction recently measured
in the core of this cluster.Comment: in press on Ap
Global phase time and path integral for string cosmological models
A global phase time is identified for homogeneous and isotropic cosmological
models yielding from the low energy effective action of closed bosonic string
theory. When the Hamiltonian constraint allows for the existence of an
intrinsic time, the quantum transition amplitude is obtained by means of the
usual path integral procedure for gauge systems.Comment: 12 pages, added reference
Characterization of bipartite states using a single homodyne detector
We suggest a scheme to reconstruct the covariance matrix of a two-mode state
using a single homodyne detector plus a polarizing beam splitter and a
polarization rotator. It can be used to fully characterize bipartite Gaussian
states and to extract relevant informations on generic states.Comment: 7 pages, 1 figur
Local temperature in quantum thermal states
We consider blocks of quantum spins in a chain at thermal equilibrium,
focusing on their properties from a thermodynamical perspective. Whereas in
classical systems the temperature behaves as an intensive magnitude, a
deviation from this behavior is expected in quantum systems. In particular, we
see that under some conditions the description of the blocks as thermal states
with the same global temperature as the whole chain fails. We analyze this
issue by employing the quantum fidelity as a figure of merit, singling out in
detail the departure from the classical behavior. The influence in this sense
of zero-temperature quantum phase transitions can be clearly observed within
this approach. Then we show that the blocks can be considered indeed as thermal
states with a high fidelity, provided an effective local temperature is
properly identified. Such a result originates from typical properties of
reduced sub-systems of energy-constrained Hilbert spaces. Finally, the relation
between local and global temperature is analyzed as a function of the size of
the blocks and the system parameters.Comment: 10 pages, 10 figures. New fidelity measure with similar result
Discovery of another peculiar radial distribution of Blue Stragglers in Globular Clusters: The case of 47 Tuc
We have used high resolution WFPC2-HST and wide field ground-based
observations to construct a catalog of blue straggler stars (BSS) in the
globular cluster 47 Tuc spanning the entire radial extent of the cluster.
The BSS distribution is highly peaked in the cluster center, rapidly
decreases at intermediate radii, and finally rises again at larger radii. The
observed distribution closely resembles that discovered in M3 by Ferraro et al
(1993,1997). To date, complete BSS surveys covering the full radial extent (HST
in the center and wide field CCD ground based observations of the exterior)
have been performed for only these two clusters. Both show a bimodal radial
distribution, despite their different dynamical properties. BSS surveys
covering the full spatial extent of more globular clusters are clearly required
to determine how common bimodality is and what its consequence is for theories
of BSS formation and cluster dynamics.Comment: 21 pages, 6 figures, accepted for pubblication in Ap
The intermediate-age globular cluster NGC 1783 in the Large Magellanic Cloud
We present Hubble Space Telescope ACS deep photometry of the intermediate-age
globular cluster NGC 1783 in the Large Magellanic Cloud. By using this
photometric dataset, we have determined the degree of ellipticity of the
cluster (=0.140.03) and the radial density profile. This profile
is well reproduced by a standard King model with an extended core (r_c=24.5'')
and a low concentration (c=1.16), indicating that the cluster has not
experienced the collapse of the core.
We also derived the cluster age, by using the Pisa Evolutionary Library (PEL)
isochrones, with three different amount of overshooting (namely,
=0.0, 0.10 and 0.25). From the comparison of the observed
Color-Magnitude Diagram (CMD) and Main Sequence (MS) Luminosity Function (LF)
with the theoretical isochrones and LFs, we find that only models with the
inclusion of some overshooting (=0.10-0.25) are able to reproduce
the observables. By using the magnitude difference between the mean level of the He-clump and the flat
region of the SGB, we derive an age =1.40.2 Gyr.Comment: Accepted to publication by A
Improving the entanglement transfer from continuous variable systems to localized qubits using non Gaussian states
We investigate the entanglement transfer from a bipartite continuous-variable
(CV) system to a pair of localized qubits assuming that each CV mode couples to
one qubit via the off-resonance Jaynes-Cummings interaction with different
interaction times for the two subsystems. First, we consider the case of the CV
system prepared in a Bell-like superposition and investigate the conditions for
maximum entanglement transfer. Then we analyze the general case of two-mode CV
states that can be represented by a Schmidt decomposition in the Fock number
basis. This class includes both Gaussian and non Gaussian CV states, as for
example twin-beam (TWB) and pair-coherent (TMC, also known as two-mode-coher
ent) states respectively. Under resonance conditions, equal interaction times
for both qubits and different initial preparations, we find that the
entanglement transfer is more efficient for TMC than for TWB states. In the
perspective of applications such as in cavity QED or with superconducting
qubits, we analyze in details the effects of off-resonance interactions
(detuning) and different interaction times for the two qubits, and discuss
conditions to preserve the entanglement transfer.Comment: revised version, 11 pages, 7 figures (few of them low-res
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