4,276 research outputs found
Foreground and background dust in star cluster directions
This paper compares reddening values E(B-V) derived from the stellar content
of 103 old open clusters and 147 globular clusters of the Milky Way with those
derived from DIRBE/IRAS 100 micron dust emission in the same directions. Star
clusters at |b|> 20 show comparable reddening values between the two methods,
in agreement with the fact that most of them are located beyond the disk dust
layer. For very low galactic latitude lines of sight, differences occur in the
sense that DIRBE/IRAS reddening values can be substantially larger, suggesting
effects due to the depth distribution of the dust. The differences appear to
arise from dust in the background of the clusters consistent with a dust layer
where important extinction occurs up to distances from the Plane of ~ 300 pc.
For 3 % of the sample a significant background dust contribution might be
explained by higher dust clouds. We find evidence that the Milky Way dust lane
and higher dust clouds are similar to those of several edge-on spiral galaxies
recently studied in detail by means of CCD imaging.Comment: manuscript in LATEX with 14 pages, 8 figures .ps Accepted for
Astronomy and Astrophysics main journal on 13.04.200
Discovery of three optical open clusters in the Galaxy
We report the discovery of three optical open clusters in the Milky Way. Two
clusters are in Scutum (Cluster1 at l=18.44 degrees and b=-0.42 degrees, and
Cluster2 at l=19.60 degrees and b=-1.02 degrees), thus projected not far from
the Galactic center direction, and the other is in Canis Major (Cluster3 at
l=235.61 degrees and b=-4.10 degrees), near the anti-center direction. Cluster3
is less populous than Clusters 1 and 2, but presents evidence of being a
physical system. The objects were found optically by inspecting maps obtained
from the Guide Star Catalogue and images from the Digitized Sky Survey. No
previous identification of cluster has been reported in each area so far. The
analysis was carried out with 2MASS photometry in J and H. For Cluster1 we
derive an age of 25 Myr, a reddening E(B-V)=2.18 and a distance from the Sun
1.64kpc; for Cluster2, age of 500Myr, E(B-V)=0.91 and distance 2.19kpc; finally
for Cluster3, age 32-100Myr, E(B-V)=0.94 and distance of 3.93kpc. Luminosity
and mass functions are derived for Clusters1 and 2 which, in turn, allowed us
to estimate their observed masses as 147 and 89 solar masses, respectively.
Estimated total masses, by extrapolating the mass functions to 0.08 solar mass,
amount to 382 and 614 solar masses, for the two clusters. Cluster3 has an
observed mass of 55 solar masses. The present results indicate that further
searches in the optical might still reveal new open clusters, and more so in
infrared bands.Comment: accepted to Astronomy and Astrophysics, 9 figure
Influence of pions on the hadron-quark phase transition
In this work we present the features of the hadron-quark phase transition
diagrams in which the pions are included in the system. To construct such
diagrams we use two different models in the description of the hadronic and
quark sectors. At the quark level, we consider two distinct parametrizations of
the Polyakov-Nambu-Jona-Lasinio (PNJL) models. In the hadronic side, we use a
well known relativistic mean-field (RMF) nonlinear Walecka model. We show that
the effect of the pions on the hadron-quark phase diagrams is to move the
critical end point (CEP) of the transitions lines. Such an effect also depends
on the value of the critical temperature (T_0) in the pure gauge sector used to
parametrize the PNJL models. Here we treat the phase transitions using two
values for T_0, namely, T_0 = 270 MeV and T_0 = 190 MeV. The last value is used
to reproduce lattice QCD data for the transition temperature at zero chemical
potential.Comment: 3 pages. Proceedings of XXXV Reuni\~ao de Trabalhos sobre F\'isica
Nuclear no Brasil 201
Interference phenomena, chiral bosons and Lorentz invariance
We have studied the theory of gauged chiral bosons and proposed a general
theory, a master action, that encompasses different kinds of gauge field
couplings in chiral bosonized theories with first-class chiral constraints. We
have fused opposite chiral aspects of this master action using the soldering
formalism and applied the final action to several well known models. The
Lorentz rotation permitted us to fix conditions on the parameters of this
general theory in order to preserve the relativistic invariance. We also have
established some conditions on the arbitrary parameter concerned in a chiral
Schwinger model with a generalized constraint, investigating both covariance
and Lorentz invariance. The results obtained supplements the one that shows the
soldering formalism as a new method of mass generation.Comment: 11 pages, RevTex(twocolumn). Final version to appear in Physiscal
Review
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