1,615 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
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
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
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&
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
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
Frequency-dependent Thermal Response of the Charge System and Restricted Sum Rules in La(2-x)Sr(x)CuO(4)
By using new and previous measurements of the -plane conductivity
of LaSrCuO (LSCO) it is shown that
the spectral weight
obeys the same law which holds for a conventional
metal like gold, for 's below the plasma frequency. However
, which measures the "thermal response" of the charge system, in
LSCO exhibits a peculiar behavior which points towards correlation effects. In
terms of hopping models, is directly related to an energy scale
, smaller by one order of magnitude than the full bandwidth .Comment: 4 pages with 3 fig
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