Abstract. Field-channelled accretion flows occur in a variety of astrophysical objects, including T Tauri stars, magnetic cataclysmic variables and X-ray pulsars. We consider a curvilinear coordinate system and derive a general hydrodynamic formulation for accretion onto stellar objects confined by a stellar dipole magnetic field. The hydrodynamic equations are solved to determine the velocity, density and temperature profiles of the flow. We use accreting magnetic white-dwarf stars as an illustrative example of astrophysical applications. Our calculations show that the compressional heating due to the field geometry is as important as radiative cooling and gravity in determining the structure of the post-shock flow in accreting white-dwarf stars. The generalisation of the formulation to accretion flows channelled by higher-order fields and the applications to other astrophysical systems are discussed.

We investigate the hydrodynamics of accretion channelled by a dipolar magnetic field (funnel flows). We consider situations in which the electrons and ions in the flow cannot maintain thermal equilibrium [two-temperature (2T) effects] due to strong radiative loss, and determine the effects on the keV X-ray properties of the systems. We apply this model to investigate the accretion shocks of white dwarfs in magnetic cataclysmic variables (mCVs). We have found that the incorporation of 2T effects could harden the keV X-rays. Also, the dipolar model yields harder X-ray spectra than the standard planar model if white dwarf is sufficiently massive ( 1 M ). When fitting observed keV X-ray spectra of mCVs, the inclusion of 2T hydrodynamics and a dipolar accretion geometry lowers estimates for white dwarf masses when compared with masses inferred from models excluding these effects. We find mass reductions 9 per cent in the most massive cases.

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Neste artigo é feita uma análise dos trabalhos aeronáuticos de Júlio Cézar Ribeiro de Souza, inventor paraense famoso no Brasil durante a década de 1880. Ribeiro de Souza foi o criador de um sistema de navegação aérea amplamente discutido no Instituto Politécnico Brasileiro, que não chegou na época a um acordo sobre a funcionabilidade do invento. Alguns autores procuraram atribuir a Souza a invenção do dirigível -notadamente Fernando Medina do Amaral (1926-2001) e Luís Carlos Bassalo Crispino -, mérito pertencente a Alberto Santos Dumont. Utilizando conhecimentos aerodinâmicos básicos, porém, o presente estudo evidencia que o Sistema Júlio Cézar, se concretizado, teria se mostrado absolutamente ineficaz.

Abstract.A hydrodynamic formulation for accretion flow channeled by a dipolar magnetic field is constructed using a curvi-linear coordinate system natural to the field structure. We solve the hydrodynamic equations and determine the velocity, density and temperature profiles of the post-shock accretion flow. The results are applied to accretion flows in intermediate polars. We have found that for systems with massive white dwarfs (~ 1 M Q ) the temperature profiles in the flow can differ significantly to those obtained from models in which the accretion column is assumed to be cylindrical.

Bartolomeu Lourenço de Gusmão foi o primeiro inventor e cientista brasileiro, célebre pela criação do balão a ar quente em 1709. Nos 300 anos de sua mais famosa invenção, este artigo apresenta uma nova biografia do fundador da Aerostática e um estudo original dos seus inventos.