5,063 research outputs found
Integrated properties of mass segregated star clusters
In this contribution we study integrated properties of dynamically segregated
star clusters. The observed core radii of segregated clusters can be 50%
smaller than the ``true'' core radius. In addition, the measured radius in the
red filters is smaller than those measured in blue filters. However, these
difference are small (), making it observationally challenging to
detect mass segregation in extra-galactic clusters based on such a comparison.
Our results follow naturally from the fact that in nearly all filters most of
the light comes from the most massive stars. Therefore, the observed surface
brightness profile is dominated by stars of similar mass, which are centrally
concentrated and have a similar spatial distribution.Comment: 2 pages, 2 figures. To appear in proceedings of the 246th IAU
symposium on "Dynamical evolution of dense stellar systems"; acknowledgements
include
Comment on "Spin-1 aggregation model in one dimension"
M. Girardi and W. Figueiredo have proposed a simple model of aggregation in
one dimension to mimic the self-assembly of amphiphiles in aqueous solution
[Phys. Rev. E 62, 8344 (2000)]. We point out that interesting results can be
obtained if a different set of interactions is considered, instead of their
choice (the s=1 Ising model).Comment: Accepted for publication in Phys. Rev.
The WIYN Open Cluster Study Photometric Binary Survey: Initial Findings for NGC 188
The WIYN open cluster study (WOCS) has been working to yield precise
magnitudes in the Johnson-Kron-Cousins UBVRI system for all stars in the field
of a selection of ``prototypical'' open clusters. Additionally, WOCS is using
radial velocities to obtain orbit solutions for all cluster binary stars with
periods of less than 1000 days. Recently, WOCS is being expanded to include the
near-infrared JHK_s (deep ground-based plus 2MASS) and mid-infrared ([3.6],
[4.5], [5.8], [8.0]) photometry from Spitzer/IRAC observations. This
multi-wavelength data (0.3--8.0 microns) allows us photometrically to identify
binaries, with mass ratios from 1.0--0.3, across a wide range of primary
masses. The spectral energy distribution (SED) fitter by Robitaille et al.
(2007) is used to fit the fluxes of 10--12 bands, converted from the observed
magnitudes, to Kurucz stellar models. Using this photometric technique, we find
that NGC 188 has a binary fraction of 36--49% and provide a star-by-star
comparison to the WOCS radial velocity-based binary study.Comment: 2 pages, 2 figures, Conference Proceedings from "Dynamical Evolution
of Dense Stellar Systems'', IAU Symposium 246, Eds. E. Vesperini, M. Giersz,
& A. Sill
The dynamical status of ZwCl 2341.1+0000: a very elongated galaxy structure with a complex radio emission
We study the dynamical status of the galaxy system ZwCl 2341.1+0000, a
filamentary multi-Mpc galaxy structure associated with a complex diffuse radio
emission. Our analysis is mainly based on new spectroscopic data for 128
galaxies acquired at the TNG telescope. We also use optical data available in
the SDSS and X-ray data from the Chandra archive. We select 101 cluster member
galaxies and compute the cluster redshift ~0.2693 and the global LOS
velocity dispersion ~1000 km/s. Our optical analysis agrees with the presence
of at least three, likely four or more, optical subclusters causing the SSE-NNW
elongation of the galaxy distribution and a significant velocity gradient in
the S-N direction. In particular, we detect an important low-velocity subclump
in the southern region, roughly coincident with the brightest peak of the
diffuse radio emission but with a clear offset between the optical and radio
peaks. We also detect one (or two) optical subcluster(s) at north, in
correspondence with the second brightest radio emission, and another one in the
central cluster region, where a third diffuse radio source has been recently
detected. A more refined analysis involving the study of the 2D galaxy
distribution suggests an even more complex structure. As for the X-ray
analysis, we confirm the SSE-NNW elongation of the intracluster medium and
detect four significant peaks. The X-ray emission is strongly asymmetric and
offsetted with respect to the galaxy distribution, thus suggesting a merger
caught in the phase of post-core-core passage. Our findings support two
possible hypotheses for the nature of the diffuse radio emission of ZwCl
2341.1+0000: a 2 relics+halo scenario or diffuse emission associated with the
infall and merging of several galaxy groups during the first phase of the
cluster formation.Comment: 14 pages, 14 figures, 4 tables; MNRAS in pres
Internal dynamics of the galaxy cluster Abell 959
The connection of cluster mergers with the presence of extended, diffuse
radio sources in galaxy clusters is still being debated. In this paper we aim
to obtain new insights into the internal dynamics of Abell 959, showing
evidence of a diffuse radio source, analyzing velocities and positions of
member galaxies. Our analysis is based on redshift data for 107 galaxies in the
cluster field acquired at the Telescopio Nazionale Galileo. We also use
photometric data from the Sloan Digital Sky Survey (Data Release 6). We combine
galaxy velocities and positions to select 81 galaxies recognized as cluster
members and determine global dynamical properties. We analyze the cluster
searching for substructures by using several statistical methods. We also study
the 2D galaxy distribution in the field of the cluster. We compare our results
with those from X-ray and gravitational lensing analyses. We estimate a cluster
redshift of z=0.2883 +/- 0.0004. We detect an NE high velocity group at 5' from
the cluster center with a relative line--of--sight (LOS) velocity of ~ +1900
km/s with respect to the main system. We also detect a central, dense structure
elongated along the SE--NW direction likely connected with the two dominant
galaxies and their surrounding cores. This elongated central structure is
probably the trace of an old cluster merger. The LOS velocity dispersion of
galaxies is very high (1025 (-75/+104) km/s). The virial mass is M(<R=1.48
Mpc)= 1.15 (-0.19/+0.25) Msun. Our results suggest that this cluster is forming
along two main directions of mass accretion and show the typical
characteristics of radio clusters; i.e., it is very massive and shows a young
dynamical state. However, deeper radio observations are needed to clarify the
nature of the diffuse radio emission in Abell 959.Comment: 12 pages, 13 figures, 3 tables. Accepted for publication on Astronomy
and Astrophysic
The Euro changeover and price adjustments in Italy
By estimating a staggered price model over the period 1980q1-2010q2, this paper documents that, after the euro changeover, Italian retailers have increased the number of price adjustments, which has translated into a higher inflation rate, with a detrimental effect on the competitiveness of the Italian economy
The puzzling merging cluster Abell 1914: new insights from the kinematics of member galaxies
We analyze the dynamical state of Abell 1914, a merging cluster hosting a
radio halo, quite unusual for its structure. Our study considers spectroscopic
data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo.
We select 89 cluster members from spatial and velocity distributions. We also
use photometry Canada-France-Hawaii Telescope archives. We compute the mean
cluster redshift, =0.168, and the velocity dispersion which shows a high
value, sigma_v=1210_{-110}^{+125} km/s. From the 2D analysis we find that Abell
1914 has a NE-SW elongated structure with two galaxy clumps, that mostly merge
in the plane of the sky. Our best, but very uncertain estimate of the velocity
dispersion of the main system is sigma_v~1000 km/s. We estimate a virial mass
M_sys=1.4--2.6 10^{15} h_{70}^{-1} Msun for the whole system. We study the
merger through a simple two-body model and find that data are consistent with a
bound, outgoing substructure observed just after the core crossing. By studying
the 2D distribution of the red galaxies, photometrically selected, we show that
Abell 1914 is contained in a rich large scale structure, with two close
companion galaxy systems, known to be at z~0.17. The system at SW supports the
idea that the cluster is accreting groups from a filament aligned in the NE-SW
direction, while that at NW suggests a second direction of the accretion NW-SE.
We conclude that Abell 1914 well fits among typical clusters with radio halos.
We argue that the unusual radio emission is connected to the complex cluster
accretion and suggest that Abell 1914 resembles the well-known nearby merging
cluster Abell 754 for its particular observed phenomenology.Comment: 14 pages, 10 figures, 2 table
Stellar populations in the Galactic bulge
AIMS:The aim of this paper is to study the characteristics of the stellar
populations and the metallicity distribution in the Galactic bulge. We study
the entire stellar population, but also retrieve information using only the red
clump stars. METHODS: To study the characteristics of the stellar populations
and the metallicity distribution in the Galactic bulge, we compared the output
of the galaxy model TRILEGAL, which implements the Binney et al. (1997) bulge
model, with observations from 2MASS and OGLE-II. A minimisation procedure has
been set up to retrieve the best fitting model with different stellar
populations and metallicity distributions. RESULTS: Using the TRILEGAL code we
find that the best model resembling the characteristics of the Galactic bulge
is a model with the distance to the Galactic centre kpc, the major axis ratios of the bar , and the angle between the
Sun-centre line and the bar . Using these
parameters the best model is found for a burst of 8 Gyr, although it is almost
indistinguishable from models with ages of 9 and 10 Gyr. The metallicity
distribution found is consistent with metallicity distributions in the
literature based on spectroscopic results.Comment: A&A accepte
Galaxies in group and field environments: a comparison of optical-NIR luminosities and colors
We compare properties of galaxies in loose groups with those in field
environment by analyzing the Nearby Optical Galaxy (NOG) catalog of galaxy
systems. We consider as group galaxies, objects belonging to systems with at
least five members identified by means of the "friends of friends method", and,
as field galaxies, all galaxies with no companions. We analyze both a
magnitude--limited sample of 959 and 2035 galaxies (groups vs. field galaxies,
respectively, B<14 mag, and 2000<cz<6000 km/s) and a volume-limited sample (M_B
<-19.01 mag, 2000<cz<4000 km/s 369 group and 548 field galaxies). For all these
galaxies, blue corrected magnitudes and morphological types are available. The
cross-correlation of NOG with the 2MASS second release allow us to assign K
magnitudes and obtain B-K colors for about half of the galaxies in our samples.
We analyze luminosity and color segregation-effects in relation with the
morphological segregation. For both B and K bands, we find that group galaxies
are, on average, more luminous than field galaxies and this effect is not
entirely a consequence of the morphological segregation. After taking into
account the morphological segregation, the luminosity difference between group
and field galaxies is about 10%. When considering only very early-type galaxies
(T<-2) the difference is larger than 30%. We also find that group galaxies are
redder than field galaxies, Delta(B-K) about 0.4 mag. However, after taking
into account the morphological segregation, we find a smaller B-K difference,
poorly significant (only at the c.l. of about 80%).Comment: 11 pages, 10 eps figures, A&A in pres
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