835 research outputs found
Prospects for detectability of classical novae with INTEGRAL
Classical novae are potential gamma-ray emitters, both in lines and in a
continuum. Continuum emission (at energies between 20-30 and 511 keV) and line
emission at 511 keV are related to positron annihilation and its Comptonization
in the expanding shell; 18F is the main responsible of positron production. The
lines at 478 and 1275 keV have their origin in the decay of the radioactive
nuclei 7Be and 22Na. Updated models of nova explosions have been adopted for
the computation of the gamma-ray emission. New yields of some radioactive
isotopes directly translate into new detectability distances of classical novae
with INTEGRAL.Comment: Contributed paper at the 4th INTEGRAL Workshop, 4-8 September 2000,
Alicante (Spain). To be published in the ESA-SP series: 4 pages, 4 figure
Gamma-ray emission from novae related to positron annihilation: constraints on its observability posed by new experimental nuclear data
Classical novae emit gamma-ray radiation at 511 keV and below, with a cut-off
at around (20-30) keV, related to positron annihilation and its Comptonization
in the expanding envelope. This emission has been elusive up to now, because it
occurs at epochs well before the maximum in optical luminosity, but it could be
detected by some sensitive intrument on board a satellite, provided that the
nova is close enough and that it is observed at the right moment. The detection
of this emission, which is a challenge for the now available and for the future
gamma-ray instruments, would shed light into the physical processes occurring
in the early phases of the explosion, which are invisible in other lower energy
ranges. A good prediction of the emitted fluxes and of the corresponding
detectability distances with different instruments relies critically on a good
knowledge of reaction rates relevant to f18 destruction, which have been
subject to a strong revision after recent nuclear spectroscopy measurements.
With respect to previous results, smaller ejected masses of f18 are predicted,
leading to smaller emitted fluxes in the (20-511) keV range and shorter
detectability distances.Comment: 9 pages, 2 figures, accepted for publication in Astrophys. J. Letter
Gamma-ray emission of classical novae and its detectability by INTEGRAL
A lot of information concerning the mechanism of nova explosions will be
extracted from the possible future observations with INTEGRAL. In order to be
prepared for this task, we are performing detailed models of the gamma-ray
emission of classical novae, for a wide range of possible initial conditions.
Spectra at different epochs after the explosion and light curves for the
different lines (511, 478 and 1275 keV) and the continuum are presented, as
well as the detectability distances with INTEGRAL spectrometer SPI. New results
related to 18F synthesis related to very recent data of nuclear physics are
advanced as preliminary.Comment: 4 pages, 2 figures, to appear in "3rd INTEGRAL Workshop: The Extreme
Universe", Taormina (Italy
Nucleosynthesis in classical novae
A general review of the relevance of classical novae for the chemical
evolution of the Galaxy, as well as for Galactic radioactivity is presented. A
special emphasis is put on the pioneering work done by Jim Truran in this field
of research. The impact of recent developments in nuclear astrophysics on nova
nucleosynthesis, together with the prospects for observability of novae
radioactivities with the INTEGRAL satellite are discussed.Comment: 6 pages, invited talk, to be published in Proceedings of the
conference "Cosmic Evolution" in the honor of J. Audouze and J.W. Truran,
held at Institut d'Astrophysique de Paris, November 200
The 18F(p,a)15O reaction rate for application to nova gamma-ray emission
The 18F(p,a)15O reaction is recognized as one of the most important reaction
for nova gamma-ray astronomy as it governs the early <= 511 keV emission.
However, its rate remains largely uncertain at nova temperatures due to unknown
low-energy resonance strengths. We report here on our last results concerning
the study of the D(18F,pa)15N reaction, as well as on the determination of the
18F(p,a)15O reaction rate using the R-matrix theory. Remaining uncertainties
are discussed.Comment: Contribution to the Eighth International Symposium on Nuclei in the
Cosmos, Vancouver july 19-23. 4 pages and 2 figure
The ages of very cool hydrogen-rich white dwarfs
The evolution of white dwarfs is essentially a cooling process that depends
primarily on the energy stored in their degenerate cores and on the
transparency of their envelopes. In this paper we compute accurate cooling
sequences for carbon-oxygen white dwarfs with hydrogen dominated atmospheres
for the full range of masses of interest. For this purpose we use the most
accurate available physical inputs for both the equation of state and opacities
of the envelope and for the thermodynamic quantities of the degenerate core. We
also investigate the role of the latent heat in the computed cooling sequences.
We present separately cooling sequences in which the effects of phase
separation of the carbon-oxygen binary mixture upon crystallization have been
neglected, and the delay introduced in the cooling times when this mechanism is
properly taken into account, in order to compare our results with other
published cooling sequences which do not include a treatment of this
phenomenon. We find that the cooling ages of very cool white dwarfs with pure
hydrogen atmospheres have been systematically underestimated by roughly 1.5 Gyr
at log(L/Lo)=-4.5 for an otherwise typical 0.6 Mo white dwarf, when phase
separation is neglected. If phase separation of the binary mixture is included
then the cooling ages are further increased by roughly 10%. Cooling tracks and
cooling isochrones in several color-magnitude diagrams are presented as well.Comment: 8 Pages; ApJ, accepted for publicatio
Hypertrophic pyloric stenosis: tips and tricks for ultrasound diagnosis
We describe a systematic approach to the ultrasound (US) examination of the antropyloric region in children. US is the modality of choice for the diagnosis of hypertrophic pyloric stenosis (HPS). The imaging features of the normal pylorus and the diagnostic findings in HPS are reviewed and illustrated in this pictorial essay. Common difficulties in performing the examination and tips to help overcome them will also be discussed
Caracterización fisicoquímica de mieles monoflorales de Euphorbia resinifera
The physicochemical characteristics of Euphorbia resinifera honey were studied. Considering the low
water content, the majority of the honeys presented a proper maturity. The values of acidity
revealed the absence of inappropriate fermentation, while the low values of hydroxymethylfurfural
(0.4–16.48 mg/kg) were suitable for of unprocessed honeys. The average values for electrical
conductivity and ashes were 451 µS/cm and 1.6 g/kg, respectively. As for the mineral content, the
K was the most abundant element; Ca, Na, Mg, P, S, and Si are all present in differing quantities in
the honeys. On the other hand, Principal Components Analysis (PCA) and Stepwise Discriminant
Analysis (SDA) were applied to distinguish between three related Euphorbia honey types. PCA
showed that the cumulative variance of the two first factors explained approximately 53%. The
results of SDA showed that variables with a higher discriminant power were K, C*ab and a*, and
100% of the samples were properly classified in their corresponding class.Los parámetros fisicoquímicos de 29 de mieles monoflorales de Euphorbia resinifera fueron estudiadas.
24 parámetros, incluyendo humedad, pH, acidez (libre, lactónica y total), HMF, cenizas, conductividad
eléctrica, monosacáridos (glucosa y fructosa), contenido mineral y parámetros cromáticos fueron
analizados. Desde el punto de vista de su calidad las mieles fueron acordes con la legislación
Europea en cuanto a contenido en agua, acidez y HMF. Los valores de cenizas y conductividad
eléctrica fueron 1,6 g/kg y 451 μS/cm, respectivamente. El contenido en minerales mostró que el K es
el elemento más abundante; mientras que Ca, Na, Mg, P, S y Si se presentaron en contenidos
intermedios. En cuanto a los valores de los parámetros del color fueron típicos de mieles ámbar
claras. Se ha realizado un análisis estadístico multivariante a los datos obtenidos para diferenciar tres
especies de mieles de Euphorbia. El análisis discriminante permite diferencia las mieles por su origen
botánico siendo el contenido en K, C*ab y la variable cromática a* las variables con mayor poder
discriminate, siendo el 100% de las muestras clasificadas correctamente en su grupo
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