54,974 research outputs found
Ages and metallicities of star clusters: new calibrations and diagnostic diagrams from visible integrated spectra
We present homogeneous scales of ages and metallicities for star clusters
from very young objects, through intermediate-age ones up to the oldest known
clusters. All the selected clusters have integrated spectra in the visible
range, as well as reliable determinations of their ages and metallicities. From
these spectra equivalent widths (EWs) of KCaII, Gband(CH) and MgI metallic, and
Hdelta, Hgamma and Hbeta Balmer lines have been measured homogeneously. The
analysis of these EWs shows that the EW sums of the metallic and Balmer H
lines, separately, are good indicators of cluster age for objects younger than
10 Gyr, and that the former is also sensitive to cluster metallicity for ages
greater than 10 Gyr. We propose an iterative procedure for estimating cluster
ages by employing two new diagnostic diagrams and age calibrations based on the
above EW sums. For clusters older than 10 Gyr, we also provide a calibration to
derive their overall metal contents.Comment: 9 pages, 4 figures, accepted by A&
Lorentz-violating dimension-five operator contribution to the black body radiation
We investigate the thermodynamics of a photon gas in an effective field
theory model that describes Lorentz violations through dimension-five operators
and Horava-Lifshitz theory. We explore the electrodynamics of the model which
includes higher order derivatives in the Lagrangian that can modify the
dispersion relation for the propagation of the photons. We shall focus on the
deformed black body radiation spectrum and modified Stefan-Boltzmann law to
address the allowed bounds on the Lorentz-violating parameter.Comment: 8 pages, 6 figures. Version published in PL
Magnetism of Substitutional Co Impurities in Graphene: Realization of Single -Vacancies
We report {\it ab initio} calculations of the structural, electronic and
magnetic properties of a graphene monolayer substitutionally doped with Co
(Co) atoms. We focus in Co because among traditional ferromagnetic
elements (Fe, Co and Ni), only Co atoms induce spin-polarization in
graphene. Our results show the complex magnetism of Co substitutional impurites
in graphene, which is mapped into simple models such as the -vacancy and
Heisenberg model. The links established in our work can be used to bring into
contact the engineering of nanostructures with the results of -models in
defective graphene. In principle, the structures considered here can be
fabricated using electron irradiation or Ar ion bombardment to create
defects and depositing Co at the same time
Spectral evolution of star clusters in the Large Magellanic Cloud: I. Blue concentrated clusters in the age range 40-300 Myr
Integrated spectroscopy of a sample of 17 blue concentrated Large Magellanic
Cloud (LMC) clusters is presented and its spectral evolution studied. The
spectra span the range ~3600-6800A with a resolution of ~14A FWHM, being used
to determine cluster ages and, in connection with their spatial distribution,
to explore the LMC structure and cluster formation history. Cluster reddening
values were estimated by interpolation, using the available extinction maps. We
used two methods to derive cluster ages: (i) template matching, in which line
strengths and continuum distribution of the cluster spectra were compared and
matched to those of template clusters with known astrophysical properties, and
(ii) equivalent width (EW) method, in which new age/metallicity calibrations
were used together with diagnostic diagrams involving the sum of EWs of
selected spectral lines (KCaII, G band (CH), MgI, Hdelta, Hgamma and Hbeta).
The derived cluster ages range from 40Myr (NGC2130 and SL237) to 300Myr
(NGC1932 and SL709), a good agreement between the results of the two methods
being obtained. Combining the present sample with additional ones indicates
that cluster deprojected distances from the LMC center are related to age in
the sense that inner clusters tend to be younger. Spectral libraries of star
clusters are useful datasets for spectral classifications and extraction of
parameter information for target star clusters and galaxies. The present
cluster sample complements previous ones, in an effort to gather a spectral
library with several clusters per age bin.Comment: 13 pages, 22 figures. Accepted for publication in A&
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