Do we really know how to derive the basic PNe parameters?

How well do we know the physical/chemical properties of PNe? 1D (CLOUDY) and 3D (MOCASSIN) photoionisation codes are used in this contribution to model the PNe K 4-47 and NGC 7009 as an attempt to question whether or not the high Te (higher than 21,000K) of the K 4-47's core and the N overabundance of the outer knots in NGC 7009 are real. These are very basic parameters, obtained for Galactic PNe, e.g. nearby objects, even though with large uncertainties. Based on the comparison of the modelling with, mainly, optical images and long-slit spectroscopic data, it is suggested here that K 4-47 high Te can be explained if its core is composed of a very dense and small inner region --that matches the radio measurements-- and a lower density outer core --matching the optical observations. This approach can account for the strong auroral emission lines [OIII]4363A and [NII]5755A observed, and so for the high temperatures. This teaches us that the assumption of a homogeneous distribution of the gas is completely wrong for the core of such PN. In the case of NGC 7009 a simple 3D model that reproduces the observed geometry of this nebula is constructed. The aim of this modelling was to explore the possibility that the enhanced [NII] emission observed in the outer knots may be due to ionisation effects instead to a local N overabundance. Here it is discussed the model that can best reproduce the observations employing a homogeneous set of abundances throughout the nebula, not only for nitrogen but also for all the other elements considered.Comment: 4 pages; talk presented in the international conference Planetary Nebulae as Astronomical Tools; June 28 - July 02, 2005; Gdansk, Poland; Eds: R. Szczerba, G. Stasinska, and S. K. Gorny; AIP Conference Proceeding

Soft-excess in ULX spectra: disc emission or wind absorption?

We assess the claim that Ultra-luminous X-ray sources (ULXs) host intermediate-mass black holes (BH) by comparing the cool disc-blackbody model with a range of other models, namelly a more complex physical model based on a power-law component slightly modified at various energies by smeared emission/absorption lines from highly-ionized gas. Our main conclusion is that the presence of a soft excess, or a soft deficit, depends entirely on the energy range to which we choose to fit the ``true'' power-law continuum; hence, we argue that those components should not be taken as evidence for accretion disc emission, nor used to infer BH masses. We speculate that bright ULXs could be in a spectral state similar to (or an extension of) the steep-power-law state of Galactic BH candidates, in which the disc is completely comptonized and not directly detectable, and the power-law emission may be modified by the surrounding, fast-moving, ionized gas.Comment: To appear in the proceedings of "The Multicoloured Landscape of Compact Objects and their Explosive Progenitors: Theory vs. Observations", Cefalu', Sicily, June 11-24, 2006 (AIP). Compilation needs specific AIP .clo, .cls, .sty and .tex files (included along with the paper .tex file and figures

Investigating the effects of the QCD dynamics in the neutrino absorption by the Earth's interior at ultrahigh energies

The opacity of the Earth to incident ultra high energy neutrinos is directly connected with the behaviour of the neutrino - nucleon ($\sigma^{\nu N}$) cross sections in a kinematic range utterly unexplored. In this work we investigate how the uncertainties in $\sigma^{\nu N}$ due the different QCD dynamic models modify the neutrino absorption while they travel across the Earth. In particular, we compare the predictions of two extreme scenarios for the high energy behaviour of the cross section, which are consistent with the current experimental data. The first scenario considered is based on the solution of the linear DGLAP equations at small-$x$ and large-$Q^2$, while the second one take into account the unitarity effects in the neutrino - nucleon cross section by the imposition of the Froissart bound behaviour in the nucleon structure functions at large energies. Our results indicate that probability of absorption and the angular distribution of neutrino events are sensitive to the the QCD dynamics at ultra high energies.Comment: 6 pages, 3 figures. Improved version to be published in Physical Review

Heavy Quark Production in Ultra High Energy Cosmic Ray Interactions

In this paper we present a comprehensive study of the heavy quark production in ultra high energy cosmic ray interactions in the atmosphere considering that the primary cosmic ray can be either a photon, neutrino or a proton. The analysis is performed using a unified framework -- the dipole formalism --- and the saturation effects, associated to the physical process of parton recombination, are taken into account. We demonstrate that the contribution of heavy quarks for cosmic ray interactions is in general non-negligible and can be dominant depending of the process considered. Moreover, our results indicate that new dynamical mechanisms should be included in order to obtain reliable predictions for the heavy quark production in $pp$ collisions at ultra high cosmic ray energies.Comment: 8 pages, 5 figures. Enlarged version to be published in Astroparticle Physic