7,359 research outputs found
Shallow extra mixing in solar twins inferred from Be abundances
Lithium and beryllium are destroyed at different temperatures in stellar
interiors. As such, their relative abundances offer excellent probes of the
nature and extent of mixing processes within and below the convection zone. We
determine Be abundances for a sample of eight solar twins for which Li
abundances have previously been determined. The analyzed solar twins span a
very wide range of age, 0.5-8.2 Gyr, which enables us to study secular
evolution of Li and Be depletion. We gathered high-quality UVES/VLT spectra and
obtained Be abundances by spectral synthesis of the Be II 313 nm doublet. The
derived beryllium abundances exhibit no significant variation with age. The
more fragile Li, however, exhibits a monotonically decreasing abundance with
increasing age. Therefore, relatively shallow extra mixing below the convection
zone is necessary to simultaneously account for the observed Li and Be behavior
in the Sun and solar twins
Soliton Stability in Systems of Two Real Scalar Fields
In this paper we consider a class of systems of two coupled real scalar
fields in bidimensional spacetime, with the main motivation of studying
classical or linear stability of soliton solutions. Firstly, we present the
class of systems and comment on the topological profile of soliton solutions
one can find from the first-order equations that solve the equations of motion.
After doing that, we follow the standard approach to classical stability to
introduce the main steps one needs to obtain the spectra of Schr\"odinger
operators that appear in this class of systems. We consider a specific system,
from which we illustrate the general calculations and present some analytical
results. We also consider another system, more general, and we present another
investigation, that introduces new results and offers a comparison with the
former investigations.Comment: 16 pages, Revtex, 3 f igure
The solar, exoplanet and cosmological lithium problems
We review three Li problems. First, the Li problem in the Sun, for which some
previous studies have argued that it may be Li-poor compared to other Suns.
Second, we discuss the Li problem in planet hosting stars, which are claimed to
be Li-poor when compared to field stars. Third, we discuss the cosmological Li
problem, i.e. the discrepancy between the Li abundance in metal-poor stars
(Spite plateau stars) and the predictions from standard Big Bang
Nucleosynthesis. In all three cases we find that the "problems" are naturally
explained by non-standard mixing in stars.Comment: Astrophysics and Space Science, in press. New version has one
reference correcte
Remote sensing applied to geological mapping; comparative geomorphology and identification of mineral zones of zinc and lead in the region of Vazante, MG
The author has identified the following significant results. Results showed that the black and white aerial photographs and the color infrared transparencies were efficient for mapping of three lithological units of the Paraopeba formation and for mineralized zones identification, respectively. Multispectral transparencies of I2S made it easier to separate dolomites, which were the rocks conditioning zinc and lead mineralization. Statistical analysis of morphometric indexes obtained from black and white photographs and topographic charts showed significant difference among three lithological units of Paraopeba formation which can be defined as Crest, Hilly, and Karstic reliefs
Interplay of tidal evolution and stellar wind braking in the rotation of stars hosting massive close-in planets
This paper deals with the application of the creep tide theory (Ferraz-Mello,
Cel. Mech. Dyn. Astron. vol. 116, 109, 2013) to the study of the rotation of
stars hosting massive close-in planets. The stars have nearly the same tidal
relaxation factors as gaseous planets and the evolution of their rotation is
similar to that of close-in hot Jupiters: they tidally evolve towards a
stationary solution. However, stellar rotation may also be affected by stellar
wind braking. Thus, while the rotation of a quiet host star evolves towards a
stationary attractor with a frequency () times the orbital mean-motion
of the companion, the continuous loss of angular momentum in an active star
displaces the stationary solution towards slower values: Active host stars with
big close-in companions tend to have rotational periods larger than the orbital
periods of their companions. The study of some hypothetical examples shows that
because of tidal evolution, the rules of gyrochronology cannot be used to
estimate the age of one system with a large close-in companion, no matter if
the star is quiet or active, if the current semi-major axis of the companion is
smaller than 0.03--0.04 AU. Details on the evolution of the systems: CoRoT
LRc06E21637, CoRoT-27, Kepler-75, CoRoT-2, CoRoT-18, CoRoT-14 and on
hypothetical systems with planets of mass 1--4 M_Jup in orbit around a star
similar to the Sun are given.Comment: 22 pages, 8 figures; Publication in Ap
A Remark on Lorentz Violation at Finite Temperature
We investigate the radiatively induced Chern-Simons-like term in
four-dimensional field theory at finite temperature. The Chern-Simons-like term
is temperature dependent and breaks the Lorentz and CPT symmetries. We find
that this term remains undetermined although it can be found unambiguously in
different regularization schemes at finite temperature.Comment: To appear in JHEP, 8 pages, 1 eps figure, minor changes and
references adde
Productive performance of goats fed with leaves of banana tree in the semi-arid region of Brazil.
Productive performance of goats kept under buffel grass pasture and supplemented with umbuzeiro fruits.
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