1,164 research outputs found
UV observations of the globular cluster M10 from HST and GALEX. The BSS population
We present a combination of high-resolution Hubble Space Telescope and
wide-field ground-based and Galaxy Evolution Explorer data of the Galactic
Globular Cluster M10 (NGC6254). By using this large data-set we determined the
center of gravity of the cluster and we built its density profile from star
counts over its entire radial extension. We find that the density profile is
well reproduced by a single-mass King model with structural parameters c=1.41
and r_c=41". We also studied the Blue Straggler Star population and its radial
distribution. We count a total number of 120 BSS within the tidal radius. Their
radial distribution is bimodal: highly peaked in the cluster center, decreasing
at intermediate distances and rising again outwards. We discuss these results
in the context of the dynamical clock scheme presented by Ferraro et al. (2012)
and of recent results about the radial distribution of binary systems in this
cluster.Comment: Accepted for publication by ApJ; 26 pages, 11 figures, 1 tabl
Measuring Ages and Elemental Abundances from Unresolved Stellar Populations: Fe, Mg, C, N, and Ca
We present a method for determining mean light-weighted ages and abundances
of Fe, Mg, C, N, and Ca, from medium resolution spectroscopy of unresolved
stellar populations. The method, pioneered by Schiavon (2007), is implemented
in a publicly available code called EZ_Ages. The method and error estimation
are described, and the results tested for accuracy and consistency, by
application to integrated spectra of well-known Galactic globular and open
clusters. Ages and abundances from integrated light analysis agree with studies
of resolved stars to within +/-0.1 dex for most clusters, and to within +/-0.2
dex for nearly all cases. The results are robust to the choice of Lick indices
used in the fitting to within +/-0.1 dex, except for a few systematic
deviations which are clearly categorized. The realism of our error estimates is
checked through comparison with detailed Monte Carlo simulations. Finally, we
apply EZ_Ages to the sample of galaxies presented in Thomas et al. (2005) and
compare our derived values of age, [Fe/H], and [alpha/Fe] to their analysis. We
find that [alpha/Fe] is very consistent between the two analyses, that ages are
consistent for old (Age > 10 Gyr) populations, but show modest systematic
differences at younger ages, and that [Fe/H] is fairly consistent, with small
systematic differences related to the age systematics. Overall, EZ_Ages
provides accurate estimates of fundamental parameters from medium resolution
spectra of unresolved stellar populations in the old and intermediate-age
regime, for the first time allowing quantitative estimates of the abundances of
C, N, and Ca in these unresolved systems. The EZ_Ages code can be downloaded at
http://www.ucolick.org/~graves/EZ_Ages.htmlComment: Accepted to ApJ
The Near Infrared NaI Doublet Feature in M Stars
The NaI near-infrared doublet has been used to indicate the dwarf/giant
population in composite systems, but its interpretation is still a contentious
issue. In order to understand the behaviour of this controversial feature, we
study the observed and synthetic spectra of cool stars. We conclude that the
NaI infrared feature can be used as a dwarf/giant discriminator. We propose a
modified definition of the NaI index by locating the red continuum at 8234
angstrons and by measuring the equivalent width in the range 8172-8197
angstrons, avoiding the region at lambda > 8197 angstrons, which contains VI,
ZrI, FeI and TiO lines. We also study the dependence of this feature on stellar
atmospheric parameters.Comment: 9 pages, (TeX file) + 7 Figures in Postscript format. Accepted for
publication in The Astrophysical Journa
An optimal estimator for the CMB-LSS angular power spectrum and its application to WMAP and NVSS data
We use a Quadratic Maximum Likelihood (QML) method to estimate the angular
power spectrum of the cross-correlation between cosmic microwave background and
large scale structure maps as well as their individual auto-spectra. We
describe our implementation of this method and demonstrate its accuracy on
simulated maps. We apply this optimal estimator to WMAP 7-year and NRAO VLA Sky
Survey (NVSS) data and explore the robustness of the angular power spectrum
estimates obtained by the QML method. With the correction of the declination
systematics in NVSS, we can safely use most of the information contained in
this survey. We then make use of the angular power spectrum estimates obtained
by the QML method to derive constraints on the dark energy critical density in
a flat CDM model by different likelihood prescriptions. When using
just the cross-correlation between WMAP 7 year and NVSS maps with 1.8
resolution, the best-fit model has a cosmological constant of approximatively
70% of the total energy density, disfavouring an Einstein-de Sitter Universe at
more than 2 CL (confidence level).Comment: 12 pages, 12 figure
A Panchromatic Study of the Globular Cluster NGC 1904. I: The Blue Straggler Population
By combining high-resolution (HST-WFPC2) and wide-field ground based (2.2m
ESO-WFI) and space (GALEX) observations, we have collected a multi-wavelength
photometric data base (ranging from the far UV to the near infrared) of the
galactic globular cluster NGC1904 (M79). The sample covers the entire cluster
extension, from the very central regions up to the tidal radius. In the present
paper such a data set is used to study the BSS population and its radial
distribution. A total number of 39 bright () BSS has been
detected, and they have been found to be highly segregated in the cluster core.
No significant upturn in the BSS frequency has been observed in the outskirts
of NGC 1904, in contrast to other clusters (M 3, 47 Tuc, NGC 6752, M 5) studied
with the same technique. Such evidences, coupled with the large radius of
avoidance estimated for NGC 1904 ( core radii), indicate that
the vast majority of the cluster heavy stars (binaries) has already sunk to the
core. Accordingly, extensive dynamical simulations suggest that BSS formed by
mass transfer activity in primordial binaries evolving in isolation in the
cluster outskirts represent only a negligible (0--10%) fraction of the overall
population.Comment: ApJ accepte
Near-infrared Spectral Features in Single-aged Stellar Populations
Synthetic spectra for single-aged stellar populations of metallicities [M/H]
= -0.5, 0.0 and +0.5, ages = 3 to 17 Gyrs, and initial mass function exponents
x = 0.1 to 2.0 were built in the wavelength range 6000-10200 Angstrons. For
such we have employed the grid of synthetic spectra described in Schiavon &
Barbuy (1999), computed for the stellar parameters 2500 <= Teff <= 6000 K, -0.5
<= log g <= 5.0, [M/H] = -0.5, 0.0 and +0.5, and [alpha/Fe] = 0.0, together
with the isochrones by Bertelli et al. (1994) and Baraffe et al. (1998). The
behavior of the features NaI8190, CaII8662, TiO6600 and FeH9900 in the
integrated spectra of single stellar populations were studied in terms of
metallicity, initial mass function and age variations. The main conclusions are
that the NaI doublet is an IMF-sensitive feature, which is however sensitive
also to metallicity and age, whereas TiO, CaII and FeH are very sensitive to
metallicity and essentially insensitive to IMF and age.Comment: 13 pages + 7 figures, ApJ accepte
Uso da modelagem matemática para simulação da dinâmica da matéria orgânica em solos tropicais.
Uso da modelagem matemática para simulação da dinâmica da matéria orgânica em solos tropicais.
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