5,646 research outputs found
Dissolving star cluster candidates
We present a list of 34 neglected entries from star cluster catalogues
located at relatively high galactic latitudes ( 15) which
appear to be candidate late stages of star cluster dynamical evolution.
Although underpopulated with respect to usual open clusters, they still present
a high number density contrast as compared to the galactic field. This was
verified by means of (i) predicted model counts from different galactic
subsystems in the same direction, and (ii) Guide Star Catalog equal solid angle
counts for the object and surrounding fields. This suggests that the objects
are physical systems, possibly star clusters in the process of disruption or
their fossil remains. The sample will be useful for followup studies in view of
verifying their physi cal nature.Comment: manuscript in LATEX with 7 pages, 7 figures .ps Accepted for
Astronomy and Astrophysics main journa
Recomendação de diferentes épocas de colheita para cultivares de mandioca tipo Indústria em Alagoas.
bitstream/item/145827/1/cot-164.pd
Manejo de plantas daninhas na cultura da mandioca no Agreste Alagoano.
bitstream/item/145863/1/CT-74.pd
A simple prescription for simulating and characterizing gravitational arcs
Simple models of gravitational arcs are crucial to simulate large samples of
these objects with full control of the input parameters. These models also
provide crude and automated estimates of the shape and structure of the arcs,
which are necessary when trying to detect and characterize these objects on
massive wide area imaging surveys. We here present and explore the ArcEllipse,
a simple prescription to create objects with shape similar to gravitational
arcs. We also present PaintArcs, which is a code that couples this geometrical
form with a brightness distribution and adds the resulting object to images.
Finally, we introduce ArcFitting, which is a tool that fits ArcEllipses to
images of real gravitational arcs. We validate this fitting technique using
simulated arcs and apply it to CFHTLS and HST images of tangential arcs around
clusters of galaxies. Our simple ArcEllipse model for the arc, associated to a
S\'ersic profile for the source, recovers the total signal in real images
typically within 10%-30%. The ArcEllipse+S\'ersic models also automatically
recover visual estimates of length-to-width ratios of real arcs. Residual maps
between data and model images reveal the incidence of arc substructure. They
may thus be used as a diagnostic for arcs formed by the merging of multiple
images. The incidence of these substructures is the main factor preventing
ArcEllipse models from accurately describing real lensed systems.Comment: 12 pages, 11 figures, accepted for publication in A&
Chemically tagging the Hyades Supercluster: A homogeneous sample of F6-K4 kinematically selected northern stars
Stellar kinematic groups are kinematical coherent groups of stars that might
have a common origin. These groups are dispersed throughout the Galaxy over
time by the tidal effects of both Galactic rotation and disc heating, although
their chemical content remains unchanged. The aim of chemical tagging is to
establish that the abundances of every element in the analysis are homogeneus
among the members. We study the case of the Hyades Supercluster to compile a
reliable list of members (FGK stars) based on our chemical tagging analysis.
For a total of 61 stars from the Hyades Supercluster, stellar atmospheric
parameters (Teff, logg, xi, and [Fe/H]) are determined using our code called
StePar, which is based on the sensitivity to the stellar atmospheric parameters
of the iron EWs measured in the spectra. We derive the chemical abundances of
20 elements and find that their [X/Fe] ratios are consistent with Galactic
abundance trends reported in previous studies. The chemical tagging method is
applied with a carefully developed differential abundance analysis of each
candidate member of the Hyades Supercluster, using a well-known member of the
Hyades cluster as a reference (vB 153). We find that only 28 stars (26 dwarfs
and 2 giants) are members, i.e. that 46% of our candidates are members based on
the differential abundance analysis. This result confirms that the Hyades
Supercluster cannot originate solely from the Hyades cluster.Comment: A&A, in pres
A Born-Infeld-like f(R) gravity
Several features of an theory in which there is a maximum value for
the curvature are analyzed. The theory admits the vaccuum solutions of GR, and
also the radiation evolution for the scale factor of the standard cosmological
model. Working in the Jordan frame, a complete analysis of the phase space is
performed, and its results supported with examples obtainted by numerical
integration. In particular, we showed that theory has nonsingular cosmological
solutions which after the bounce enter a phase of de Sitter expansion and
subsequently relax to a GR-like radiation-dominated evolution.Comment: Latex file, 14 pages, 7 figures (jpg format), including more detailed
discussions than previous version, accepted for publication in Physical
Review
Globular Clusters around Galaxies in Groups
We have obtained deep photometry of NGC 1199 (in HCG 22) and NGC 6868 (in the
Telescopium group). Both galaxies are the optically brightest galaxies of their
groups. Our analysis of B and R images taken with the Keck II and the VLT/ESO
telescopes, detected a population of globular clusters around both galaxies,
with total specific frequencies S_N=1.7\pm0.6 for NGC 1199 and S_N = 1.3\pm0.6
for NGC 6868. The color distributions of the globular cluster systems shows
bimodal peaks centered at (B-R)_0 = 1.13\pm0.10 and 1.42\pm0.10 (NGC 1199) and
(B-R)_0=1.12\pm0.10 and 1.42\pm0.10 (NGC 6868).Comment: 3 pages, 1 figure. To appear in the proceedings of IAU Symp. 207,
"Extragalactic Star Clusters", eds. E. Grebel, D. Geisler, D. Minnit
Inhomogeneous vacuum energy
Vacuum energy remains the simplest model of dark energy which could drive the
accelerated expansion of the Universe without necessarily introducing any new
degrees of freedom. Inhomogeneous vacuum energy is necessarily interacting in
general relativity. Although the four-velocity of vacuum energy is undefined,
an interacting vacuum has an energy transfer and the vacuum energy defines a
particular foliation of spacetime with spatially homogeneous vacuum energy in
cosmological solutions. It is possible to give a consistent description of
vacuum dynamics and in particular the relativistic equations of motion for
inhomogeneous perturbations given a covariant prescription for the vacuum
energy, or equivalently the energy transfer four-vector, and we construct
gauge-invariant vacuum perturbations. We show that any dark energy cosmology
can be decomposed into an interacting vacuum+matter cosmology whose
inhomogeneous perturbations obey simple first-order equations.Comment: 8 pages; v2 clarified discussion of Chaplygin gas model, references
adde
- …