812 research outputs found
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.
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
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
Determinação da concentração inibitória mÃnima do óleo essencial de Cymbopogon citratus em bactérias causadoras de mastite bovina.
Observations of T Tauri Disks at Sub-AU Radii: Implications for Magnetospheric Accretion and Planet Formation
We determine inner disk sizes and temperatures for four solar-type (1-2
M) classical T Tauri stars (AS 207A, V2508 Oph, AS 205A, and PX Vul)
using 2.2 m observations from the Keck Interferometer. Nearly
contemporaneous near-IR adaptive optics imaging photometry, optical photometry,
and high-dispersion optical spectroscopy are used to distinguish contributions
from the inner disks and central stars in the interferometric observations. In
addition, the spectroscopic and photometric data provide estimates of stellar
properties, mass accretion rates, and disk co-rotation radii. We model our
interferometric and photometric data in the context of geometrically flat
accretion disk models with inner holes, and flared disks with puffed-up inner
walls. Models incorporating puffed-up inner disk walls generally provide better
fits to the data, similar to previous results for higher-mass Herbig Ae stars.
Our measured inner disk sizes are larger than disk truncation radii predicted
by magnetospheric accretion models, with larger discrepancies for sources with
higher mass accretion rates. We suggest that our measured sizes correspond to
dust sublimation radii, and that optically-thin gaseous material may extend
further inward to the magnetospheric truncation radii. Finally, our inner disk
measurements constrain the location of terrestrial planet formation as well as
potential mechanisms for halting giant planet migration.Comment: Accepted for publication in ApJ (May 1, 2005 issue
Conteúdo de compostos fenólicos e teores de açúcares redutores e não redutores em tubérculos de batata infectados com diferentes nÃveis de Meloidogyne javanica.
The Temperature Scale of Metal-Rich M Giants Based on TiO Bands: Population Synthesis in the Near Infrared
We have computed a grid of high resolution synthetic spectra for cool stars
(2500<Teff<6000 K) in the wavelength range 6000 -- 10200A, by employing an
updated line list of atomic and molecular lines, together with state-of-the-art
model atmospheres.
As a by-product, by fitting TiO bandheads in spectra of well-known M giants,
we have derived the electronic oscillator strengths of the TiO gamma prime,
delta, epsilon and phi systems. The derived oscillator strenghts for the gamma
prime, epsilon and phi systems differ from the laboratory and ab initio values
found in the literature, but are consistent with the model atmospheres and line
lists employed, resulting in a good match to the observed spectra of M giants
of known parameters.
The behavior of TiO bands as a function of the stellar parameters Teff, log g
and [Fe/H] is presented and the use of TiO spectral indices in stellar
population studies is discussed.Comment: ApJ accepted, 27 pages + 11 figures, AASLatex v4.
Science Objectives and Early Results of the DEEP2 Redshift Survey
The DEIMOS spectrograph has now been installed on the Keck-II telescope and
commissioning is nearly complete. The DEEP2 Redshift Survey, which will take
approximately 120 nights at the Keck Observatory over a three year period and
has been designed to utilize the power of DEIMOS, began in the summer of 2002.
The multiplexing power and high efficiency of DEIMOS enables us to target 1000
faint galaxies per clear night. Our goal is to gather high-quality spectra of
\~60,000 galaxies with z>0.75 in order to study the properties and large scale
clustering of galaxies at z ~ 1. The survey will be executed at high spectral
resolution, , allowing us to work
between the bright OH sky emission lines and to infer linewidths for many of
the target galaxies (for several thousand objects, we will obtain rotation
curves as well). The linewidth data will facilitate the execution of the
classical redshift-volume cosmological test, which can provide a precision
measurement of the equation of state of the Universe. This talk reviews the
project, summarizes our science goals and presents some early DEIMOS data.Comment: 12 pages, 5 figures, talk presented at SPIE conference, Aug. 200
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