Multiepoch Mulitwavelength Spectra and Models for Blazar 3C 279

Peer reviewe

Variability of the Centimeter-Submillimeter Spectrum and Polarization of 3C 273 during Outburst

Original article can be found at: http://www.journals.uchicago.edu/ApJ/--Copyright University of Chicago Press/ AASCentimeter to submillimeter total flux and polarization monitoring data are used to investigate the nature of a prominent flare in the quasar 3C 273 during 1995/6. After removal of the quiescent level, the resulting “flare spectra" are well fitted by a simple homogeneous synchrotron source model, which in turn allows the movement of the self-absorption turnover to be tracked during the flare. Both the flare amplitude/time delay relationship and the overall spectral evolution are qualitatively consistent with existing models. The early evolution of the spectrum is best determined and is shown to be in excellent agreement with the Compton stage of the Marscher & Gear shock model. However, the polarization behavior during the flare is different at millimeter and centimeter wavelengths and the observations are difficult to reconcile with a simple transverse shock. They are, however, consistent with a conical shock for which the observed polarization properties vary with distance along the jet. Such variations may be caused, for example, by a change in cone angle owing to disruption caused by the growing component of the magnetic field parallel to the jet axis or by a moderate change in viewing angle.Peer reviewe

Spectrometric study of condensed phase species of thorium and palladium-based modifiers in a complex matrix for electrothermal atomic absorption spectrometry

The chemical and morphological transformations of condensed phase species of a thorium-based modifier were studied over the temperature range 200–2500 °C, without and with the presence of aluminium and silicon as matrix components, and in some instances, arsenic as an analyte element. A similar study was also conducted with palladium as the modifier, for comparison. Results were derived using scanning electron microscopy (SEM), energy dispersive (ED) X-ray spectrometry, Raman microanalysis and attenuated total reflectance (ATR) Fourier transform-infrared (FT-IR) spectrometry. Comparable results were found using pyrolytic and non-pyrolytic graphite platforms, with processes occurring at slightly higher temperatures on the pyrolytic graphite platform. With thorium as the modifier, metal oxides were the predominant species on the platform surface at relatively low temperatures (<1500 °C), whereas metal phases became prevalent at high temperatures, when thorium and aluminium tended to behave independently from one other. Some spatial variations in the composition of the salt residues on different regions of the platform were observed (from the region closest to the slot in the tube, to the region furthest from the slot). Nonetheless, thorium metal remained on the graphite platform to higher temperatures than did aluminium metal. In the presence of arsenic, the existence of mixtures of thorium and arsenic oxides, just before the appearance temperature of gas phase arsenic atoms, was confirmed by SEM studies, ED X-ray spectra and Raman microanalysis. This suggests that any modifying effect of thorium on arsenic occurs while the modifier is in the oxide phase rather than in the metal phase. The presence of silicon added as silica, did not influence significantly the thermochemical behaviour of mixtures of thorium and aluminium. However, coexistence of silicon and arsenic oxides at the appearance temperature of the atomic absorption signal of arsenic was obtained, confirming that silicon can act as an internal modifier for arsenic. In the presence of palladium, aluminium exhibited greater interaction with the modifier; consequently, aluminium metal was retained on the platform surface to higher temperatures than thorium, which could explain how interference effects of aluminium on e.g. arsenic are avoided or reduced. Similarly, there was evidence for interaction of palladium and arsenic in the reduced state. However, when aluminium and silicon were present, the transformation of the palladium oxide to the metallic state was affected, which could diminish the modifying benefits of palladium for arsenic in the presence of aluminium

Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars

Aims: Chemical compositions and other properties of planetary nebulae around central stars of spectral types [WC], [WO], and wels are compared with those of `normal' central stars, in order to clarify the evolutionary status of each type and their interrelation. Methods: We use plasma diagnostics to derive from optical spectra the plasma parameters and chemical compositions of 48 planetary nebulae. We also reanalyze the published spectra of a sample of 167 non-WR PN. The results as well as the observational data are compared in detail with those from other studies of the objects in common. Results: The central star's spectral type is clearly correlated with electron density, temperature and excitation class of the nebula, [WC] nebulae tend to be smaller than the other types. All this corroborates the view of an evolutionary sequence from cool [WC 11] central stars inside dense, low excitation nebulae towards hot [WO 1] stars with low density, high excitation nebulae. The wels PN, however, appear to be a separate class of objects, not linked to WRPN by evolution, --abridged--Comment: 17 pages, 28 figures, Accepted in A&A. Accepted in A&

Frequency dependent core shifts and parameter estimation for the blazar 3C 454.3

We study the core shift effect in the parsec scale jet of the blazar 3C 454.3 using the 4.8 GHz - 36.8 GHz radio light curves obtained from three decades of continuous monitoring. From a piecewise Gaussian fit to each flare, time lags $\Delta t$ between the observation frequencies $\nu$ and spectral indices $\alpha$ based on peak amplitudes $A$ are determined. From the fit $\Delta t \propto \nu^{1/k_r}$, $k_r = 1.10 \pm 0.18$ indicating equipartition between the magnetic field energy density and the particle energy density. From the fit $A \propto \nu^\alpha$, $\alpha$ is in the range $-0.24$ to $1.52$. A mean magnetic field strength at 1 pc, $B_1 = 0.5 \pm 0.2$ G, and at the core, $B_{\rm core} = 46 \pm 16$ mG, are inferred, consistent with previous estimates. The measure of core position offset is $\Omega_{r\nu} = 6.4 \pm 2.8$ pc GHz$^{1/k_r}$ when averaged over all frequency pairs. Based on the statistical trend shown by the measured core radius $r_{\rm core}$ as a function of $\nu$, we infer that the synchrotron opacity model may not be valid for all cases. A Fourier periodogram analysis yields power law slopes in the range $-1.6$ to $-3.5$ describing the power spectral density shape and gives bend timescales in the range $0.52 - 0.66~$yr. This result, and both positive and negative $\alpha$, indicate that the flares originate from multiple shocks in a small region. Important objectives met in our study include: the demonstration of the computational efficiency and statistical basis of the piecewise Gaussian fit; consistency with previously reported results; evidence for the core shift dependence on observation frequency and its utility in jet diagnostics in the region close to the resolving limit of very long baseline interferometry observations.Comment: 12 pages, 11 figures (23 sub-figures), 5 tables. Accepted for publication in MNRA

Development and significance of tectonic foliations in the Hercynian Belt of NW Spain

[Resumen] En este trabajo se presenta un modelo de distribución y desarrollo de foliaciones en rocas pelíticas y samíticas dentro de un orógeno: el Macizo Herciniano del NW d e España. Estas rocas estuvieron sometidas a una deformación polifásica, con tres fases principales, en condiciones que van desde la transición diagénesis-metamorfismo hasta un metamorfismo de alto grado. Las características de las foliaciones asociadas a las distintas fases de deformaci6n varían progresivamente a medida que lo hace el metamorfismo, existiendo, no obstante, algunos saltos bruscos en dichas características, cuya situaci6n coincide con los límites entre algunas de las grandes zonas en que se divide el orógeno. En todo caso, la foliación tect6nica primaria(Sl) muestra un carácter generalizado, mientras que las otras dos (S2 y S3) presentan una distribución más irregular, apareciendo la S2 en relación con las zonas de cizalla asociadas a grandes cabalgamientos y la S3 controlada por la posición de la anisotropía previa dominante. En la formaci6n de estas foliaciones intervino, en general, de manera muy importante la disolución por presión en las áreas menos metamórficas y la recristalización orientada de filosilicatos en las más metamórficas. El análisis de las relaciones cronológicas entre cristalización metamórfica y desarrollo de foliaciones pone de manifiesto una cierta heterogeneidad espacial en el momento de aparición de los episodios metamórficos en relación con los de deformación. Esta heterogeneidad puede explicarse por las alteraciones en las condiciones P, T que produce el emplazamiento de las grandes unidades tectónicas.[Abstract] A model concerning distribution and development of foliations is presented in this paper, for pelitic and psammitic rocks in the Hercynian Belt ofNW Spain. This rocks have undergone three main deformation phases, in conditions ranging from the iagenesis-metamorphism transition to the high grade metamorphism. The features of the foliations associated to the different phases varie progressively with the metamorphism. Nevertheless, sorne abrupt changes in this features can also be found in sorne of the borders between the main tectonic units. Anyhow, the primary tectonic foliation (Si) is generalized, and the other two (S2 and S3) have a more irregular distribution, related to shear zones associated to main thrusts (S2), or to zones with a favourable possition of the main previous anisotropy (for S3)' The deformation mechanisms opperating in the development of this foliations were, mainly, pressure solution in the zones with low metamorphism, and recrystalization of orientated phyllosillicates in those with the higher metamorphism. The analysis of the chronologic relationships between metamorphic crystalization and development of the foliations in different tectonic units shows sorne differences in the age of the metamorphic episodes in relation with the deformation. These inhomogeneities can be explained by the changes in P, T conditions produced by the emplacement of the main tectonic units

Ice nucleation from aqueous NaCl droplets with and without marine diatoms

Ice formation in the atmosphere by homogeneous and heterogeneous nucleation is one of the least understood processes in cloud microphysics and climate. Here we describe our investigation of the marine environment as a potential source of atmospheric IN by experimentally observing homogeneous ice nucleation from aqueous NaCl droplets and comparing against heterogeneous ice nucleation from aqueous NaCl droplets containing intact and fragmented diatoms. Homogeneous and heterogeneous ice nucleation are studied as a function of temperature and water activity, &lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt;. Additional analyses are presented on the dependence of diatom surface area and aqueous volume on heterogeneous freezing temperatures, ice nucleation rates, &amp;omega;&lt;sub&gt;het&lt;/sub&gt;, ice nucleation rate coefficients, &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;het&lt;/sub&gt;, and differential and cumulative ice nuclei spectra, &lt;i&gt;k(T)&lt;/i&gt; and &lt;i&gt;K(T)&lt;/i&gt;, respectively. Homogeneous freezing temperatures and corresponding nucleation rate coefficients are in agreement with the water activity based homogeneous ice nucleation theory within experimental and predictive uncertainties. Our results confirm, as predicted by classical nucleation theory, that a stochastic interpretation can be used to describe the homogeneous ice nucleation process. Heterogeneous ice nucleation initiated by intact and fragmented diatoms can be adequately represented by a modified water activity based ice nucleation theory. A horizontal shift in water activity, &amp;Delta;&lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w, het&lt;/sub&gt; = 0.2303, of the ice melting curve can describe median heterogeneous freezing temperatures. Individual freezing temperatures showed no dependence on available diatom surface area and aqueous volume. Determined at median diatom freezing temperatures for &lt;i&gt;a&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt; from 0.8 to 0.99, &amp;omega;&lt;sub&gt;het&lt;/sub&gt;&lt;u&gt;~&lt;/u&gt;0.11&lt;sup&gt;+0.06&lt;/sup&gt;&lt;sub&gt;&amp;minus;0.05&lt;/sub&gt; s&lt;sup&gt;−1&lt;/sup&gt;, &lt;i&gt;J&lt;/i&gt;&lt;sub&gt;het&lt;/sub&gt;&lt;u&gt;~&lt;/u&gt;1.0&lt;sup&gt;+1.16&lt;/sup&gt;&lt;sub&gt;&amp;minus;0.61&lt;/sub&gt;&amp;times;10&lt;sup&gt;4&lt;/sup&gt; cm&lt;sup&gt;−2&lt;/sup&gt; s&lt;sup&gt;−1&lt;/sup&gt;, and &lt;i&gt;K&lt;/i&gt;&lt;u&gt;~&lt;/u&gt;6.2&lt;sup&gt;+3.5&lt;/sup&gt;&lt;sub&gt;&amp;minus;4.1&lt;/sub&gt; &amp;times;10&lt;sup&gt;4&lt;/sup&gt; cm&lt;sup&gt;−2&lt;/sup&gt;. The experimentally derived ice nucleation rates and nuclei spectra allow us to estimate ice particle production which we subsequently use for a comparison with observed ice crystal concentrations typically found in cirrus and polar marine mixed-phase clouds. Differences in application of time-dependent and time-independent analyses to predict ice particle production are discussed

X-ray emission from Planetary Nebulae. I. Spherically symmetric numerical simulations

(abridged) The interaction of a fast wind with a spherical Asymptotic Giant Branch (AGB) wind is thought to be the basic mechanism for shaping Pre-Planetary Nebulae (PPN) and later Planetary Nebulae (PN). Due to the large speed of the fast wind, one expects extended X-ray emission from these objects, but X-ray emission has only been detected in a small fraction of PNs and only in one PPN. Using numerical simulations we investigate the constraints that can be set on the physical properties of the fast wind (speed, mass-flux, opening angle) in order to produce the observed X-ray emission properties of PPNs and PNs. We combine numerical hydrodynamical simulations including radiative cooling using the code FLASH with calculations of the X-ray properties of the resulting expanding hot bubble using the atomic database ATOMDB. In this first study, we compute X-ray fluxes and spectra using one-dimensional models. Comparing our results with analytical solutions, we find some agreements and many disagreements. In particular, we test the effect of different time histories of the fast wind on the X-ray emission and find that it is determined by the final stage of the time history during which the fast wind velocity has its largest value. The disagreements which are both qualitative and quantitative in nature argue for the necessity of using numerical simulations for understanding the X-ray properties of PNs.Comment: 17 pages, accepted for publication in ApJ (July 27, 2006), uses emulateap