1,312 research outputs found
AL 3 (BH 261): a new globular cluster in the Galaxy
AL~3 (BH 261), previously classified as a faint open cluster candidate, is
shown to be a new globular cluster in the Milky Way, by means of B, V and I
Color-Magnitude Diagrams. The main feature of AL~3 is a prominent blue extended
Horizontal Branch. Its Color-Magnitude Diagrams match those of the intermediate
metallicity cluster M~5. The cluster is projected in a rich bulge field, also
contaminated by the disk main sequence. The globular cluster is located in the
Galactic bulge at a distance from the Sun d = 6.00.5 kpc. The
reddening is E(B-V)=0.360.03 and the metallicity is estimated to be [Fe/H]
-1.30.25. AL~3 is probably one of the least massive globular
clusters of the Galaxy.Comment: 6 figures. Astrophysical Journal Letters, in pres
Pfleiderer2: identification of a new globular cluster in the Galaxy
We provide evidence that indicate the star cluster Pfleiderer 2, which is
projected in a rich field, as a newly identified Galactic globular cluster.
Since it is located in a crowded field, core extraction and decontamination
tools were applied to reveal the cluster sequences in B, V and I
Color-Magnitude Diagrams (CMDs). The main CMD features of Pfleiderer 2 are a
tilted Red Giant Branch, and a red Horizontal Branch, indicating a high
metallicity around solar. The reddening is E(B-V)=1.01. The globular cluster is
located at a distance from the Sun d = 162 kpc.
The cluster is located at 2.7 kpc above the Galactic plane and at a distance
from the Galactic center of R=9.7 kpc, which is unusual for a
metal-rich globular cluster.Comment: Accepted by The Astronomical Journa
The old metal-poor open cluster ESO 92-SC05: accreted from a dwarf galaxy?
The study of old open clusters outside the solar circle can bring constraints
on formation scenarios of the outer disk. In particular, accretion of dwarf
galaxies has been proposed as a likely mechanism in the area. We use BVI
photometry for determining fundamental parameters of the faint open cluster ESO
92-SC05. Colour-Magnitude Diagrams are compared with Padova isochrones, in
order to derive age, reddening and distance. We derive a reddening E(B-V)=
0.17, and an old age of 6.0 Gyr.
It is one of the rare open clusters known to be older than 5 Gyr. A
metallicity of Z0.004 or [M/H]-0.7 is found. The rather low
metallicity suggests that this cluster might be the result of an accretion
episode of a dwarf galaxy.Comment: 11 figures: 1, 2a,b,c, 3a,b, 4a,b, 5, 6, 7 6 pages to compile with
mn2e.cls. Monthly Notices of the Royal Astronomical Society, in pres
Near Infrared properties of 12 Globular Clusters toward the inner Bulge of the Galaxy
We present near-IR Colour-Magnitude diagrams and physical parameters for a
sample of 12 galactic globular clusters located toward the inner Bulge region.
For each cluster we provide measurements of the reddening, distance,
photometric metallicity, luminosity of the horizontal branch red clump, and of
the red giant branch bump and tip. The sample discussed here together with that
presented in Valenti, Ferraro & Origlia (2007) represent the largest
homogeneous catalog of Bulge globular clusters (comprising ~ 80% of the entire
Bulge cluster population) ever studied. The compilation is available in
electronic form on the World Wide Web (http://www.bo.astro.it/~GC/ir_archive)Comment: 2 pages, 13 figures, 4 tables, accepted for publication in MNRA
Detection of Ks-excess stars in the 14Myr open cluster NGC4755
We derive the structure, distribution of MS and PMS stars and dynamical state
of the young open cluster NGC 4755. We explore the possibility that, at the
cluster age, some MS and PMS stars still present infrared excesses related to
dust envelopes and proto-planetary discs. The radial density profile follows
King's law with a core radius \rm\rc=0.7\pm0.1 pc and a limiting radius
\rm\rl=6.9\pm0.1 pc; the cluster age is . Field-star
decontamination reveals a low-MS limit at \rm\approx1.4 \ms. The core MF
() is flatter than the halo's (). NGC 4755
contains candidate PMS stars of age , and a few
evolved stars. The mass locked up in PMS, MS and evolved stars amounts to
\rm\sim1150 \ms. Proper motions show that \ks-excess MS and PMS stars are
cluster members. \ks-excess fractions in PMS and MS stars are
and respectively, consistent with the cluster age. The core is
deficient in PMS stars, as compared with MS ones. NGC 4755 hosts binaries in
the halo but they are scarce in the core. Compared to open clusters in
different dynamical states studied with similar methods, NGC 4755 fits
relations involving structural and dynamical parameters in the expected locus
for its age and mass. On the other hand, the flatter core MF probably
originates from primordial processes related to parent molecular cloud
fragmentation and mass segregation over . Star formation in NGC
4755 began ago and proceeded for about the same length of
time. Detection of \ks-excess emission in member MS stars suggests that some
circumstellar dust discs survived for , occurring both in some
MS and PMS stars for the age and spread observed in NGC 4755.Comment: 10 figs. Astronomy & Astrophysics, in pres
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&
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.
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
V, J, H and K Imaging of the Metal Rich Globular Cluster NGC 6528
New near-infrared observations of NGC6528 are presented. The JHK observations
complement a previous HST/NICMOS data set by Ortolani et al. (2001), in that
they sample a larger area, contain a more numerous sample of red giant stars,
and include the K band. Also, archival HST data sets (separated by 6.093 years)
were used to proper-motion decontaminate the near-infrared sample and extract a
clean VJHK catalogue. Using the present wide colour baseline, we compared the
cleaned colour-magnitude diagrams of NGC6528 with those of NGC 6553 and NGC104
and derived new estimates of reddening and distance, E(B-V)=0.55 and
(m-M)o=14.44 (7.7 kpc). Moreover, the morphology and location of the cleaned
red giant branch were used to derive a photometric estimate of the cluster
metallicity. The average of 10 metallicity indicators yields a mean value of
[M/H] ~ 0.0, and [Fe/H] ~-0.20 and +0.08 on the Zinn & West (1984) and Carretta
& Gratton (1997) revised metallicity scale, respectively. The best isochrone
fit to the cleaned K,V-K diagram is obtained for a 12.6 Gyr and Z=0.02
isochrone, i.e. the derived metallicity of NGC6528 turns out to be very close
to the mean of stars in the Baade's Window. Five AGB variable star candidates,
whose membership has to be confirmed spectroscopically, are bolometrically as
bright as the known long period variable stars in NGC6553. As discussed in
Guarnieri et al. (1997) for NGC6553, this may indicate that an `intermediate
age' population is not needed to account for the brightest stars in external
galaxies such as M32.Comment: 11 pages, 9 figures, A&A accepte
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