7,504 research outputs found
Spatially resolved physical and chemical properties of the planetary nebula NGC 3242
Optical integral-field spectroscopy was used to investigate the planetary
nebula NGC 3242. We analysed the main morphological components of this source,
including its knots, but not the halo. In addition to revealing the properties
ofthe physical and chemical nature of this nebula, we also provided reliable
spatially resolved constraints that can be used for future photoionisation
modelling of the nebula. The latter is ultimately necessary to obtain a fully
self-consistent 3D picture of the physical and chemical properties of the
object. The observations were obtained with the VIMOS instrument attached to
VLT-UT3. Maps and values for specific morphological zones for the detected
emission-lines were obtained and analysed with routines developed by the
authors to derive physical and chemical conditions of the ionised gas in a 2D
fashion. We obtained spatially resolved maps and mean values of the electron
densities, temperatures, and chemical abundances, for specific morphological
structures in NGC 3242. These results show the pixel-to-pixel variations of the
the small- and large-scale structures of the source. These diagnostic maps
provide information free from the biases introduced by traditional single
long-slit observations. In general, our results are consistent with a uniform
abundance distribution for the object, whether we look at abundance maps or
integrated fluxes from specified morphological structures. The results indicate
that special care should be taken with the calibration of the data and that
only data with extremely good signal-to-noise ratio and spectral coverage
should be used to ensure the detection of possible spatial variations.Comment: 11 pages, 8 figures accepted for publication in Astronomy &
Astrophysic
The Local Group Symbiotic Star Population and its Weak Relation with Type Ia Supernovae
Here we study the symbiotic stars (SySt) population and its relation with
type Ia supernovae (SNe Ia) in the galaxies of the Local Group. SySt are low-
and/or intermediate-mass evolved binary systems where a white dwarf (WD)
accretes mass from a giant star. A fraction of these WDs can become massive
enough to reach the Chandrasekhar mass. Therefore, SySt have been considered as
potential SNe Ia progenitors. Taking two approaches, one empirical and another
statistical, we estimated the SySt population on the Galaxy as having a minimum
value of and a expected one of . For Local
Group dwarfs galaxies, the computed SySt population ranges from 2 to 4 orders
of magnitudes lower. Concerning the SNe Ia with SySt progenitors, our general
result is that SySt are not the main SNe Ia progenitors. On the other hand, we
still expect that about 0.5-8% of the SNe Ia have symbiotic progenitors in the
Milky Way, while the majority of the - low-mass - dwarfs galaxies did not
experience a symbiotic type Ia supernova.Comment: 5 pages, 2 figures, 3 table
Enhancement of prompt photons in ultrarelativistic proton-proton collisions from nonlinear gluon evolution at small-
In this paper we estimate the influence of nonlinear gluon evolution in the
production of prompt photons at the LHC pp collider. We assume the validity of
collinear factorization and consider the EHKQS parton distributions, which are
solutions of the GLR-MQ evolution equations and describe quite well the DESY
HERA data, as input in our calculations. We find that both single and
double photon production are enhanced for low- photons and central
rapidities, while this effect is absent for the high- photons. The
implications of this effect for the Quark-Gluon Plasma searches and for the QCD
background to Higgs are also discussed.Comment: 4 pages, 4 figures. Version to be published in Physical Review
Análise de tendências de temperatura mÃnima do Brasil.
A concentração dos gases de efeito estufa vem aumentando consideravelmente nos últimos 150 anos e tem sido considerado como principal causa do aquecimento global no planeta nesse perÃodo. O objetivo do trabalho foi analisar as tendências de temperatura mÃnima nas cinco regiões do Brasil. Foram calculadas as temperaturas mÃnimas mensais e anuais de cada estação por meio da média aritmética dos valores diários e mensais, respectivamente. Calculou-se também a média móvel de cinco anos e o desvio da temperatura mÃnima em relação a média da temperatura mÃnima no perÃodo de estudo de cada estação meteorológica. As análises dos desvios da temperatura mÃnima anual, em relação à média da série de dados de cada estação meteorológica analisada, indicaram tendências de aumento significativo nas cinco regiões do paÃs.CBA 2009
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